unchecked assignment ignore

DEV Community

Posted on Jun 1, 2023

How to Avoid Unchecked Casts in Java Programs

Unchecked cast refers to the process of converting a variable of one data type to another data type without checks by the Java compiler.

This operation is unchecked because the compiler does not verify if the operation is valid or safe. Unchecked casts can lead to runtime errors, such as ClassCastException, when the program tries to assign an object to a variable of an incompatible type.

Hence, it is important to avoid unchecked casts in Java programs to prevent potential errors and ensure the program's reliability.

Consequences of Unchecked Casts

In Java programs, unchecked casts can lead to several issues. The most common problem is a ClassCastException at runtime, which occurs when we try to cast an object to a wrong type. This can cause the program to crash or behave unexpectedly.

Unchecked casts also violate the type safety of the Java language, which can lead to bugs that are difficult to detect and debug. Additionally, unchecked casts can make the code less readable and maintainable, as they hide the true type of objects and dependencies between components.

Therefore, it is important to avoid unchecked casts and use other mechanisms, such as generics or polymorphism, to ensure type safety and code quality in Java programs.

How Unchecked Casts Occur

Unchecked casts in Java programs occur when an object of one type is assigned to a reference of another type without proper type checking. This can happen when a programmer assumes that a reference to a superclass is actually a reference to its subclass and tries to cast it into that subclass. If the assumption is incorrect, the cast will result in a ClassCastException at runtime.

Unchecked casts can also occur when dealing with raw types, which are generic types without any type parameters specified. In such cases, the compiler cannot perform type checking and the programmer must ensure that the proper type conversions are made. Failing to do so can result in unchecked casts and potential runtime errors.

Why unchecked casts are problematic

In Java, unchecked casts allow a programmer to cast any object reference to any other reference type without providing any type information at compile-time. While this flexibility may seem useful, it can lead to serious run-time errors. If the object being casted is not actually of the type specified, a ClassCastException will occur at run-time.

Unchecked casts can cause difficult-to-debug errors in large and complex codebases, as it may not be immediately clear where the error originated. Additionally, unchecked casts can undermine Java's type system, creating code that is harder to read, maintain, and reason about. As a result, avoiding unchecked casts should be a priority when writing Java programs.

Examples of Unchecked Casts in Java

Unchecked casts are a common source of Java program errors. Here are some examples of unchecked casts:

This cast statement above can result in a class cast exception if the object referred to by obj is not a List.

In this case, the cast could fail at runtime if the array contains objects of a type other than String.

Finally, this cast could fail if the object referred to by obj is not a Map.

Using Generics to Avoid Unchecked Casts in Java

In Java, Generics is a powerful feature that allows you to write classes and methods that are parameterized by one or more types. Generics are a way of making your code more type-safe and reusable. With generics, you can define classes and methods that work on a variety of types, without having to write separate code for each type.

Using generics in Java programs has several advantages. It enables type safety at compile-time, which can prevent ClassCastException errors at runtime. With generics, the compiler can detect type mismatches and prevent them from happening, which leads to more robust and reliable code. It also allows for code reuse without sacrificing type safety and improve performance by avoiding unnecessary casting and allowing for more efficient code generation.

Generics allow Java developers to create classes and methods that can work with different data types. For example, a List can be defined to hold any type of object using generics. Here's an example:

In this example, we create a List that holds String objects. We can add String objects to the list and iterate over them using a for-each loop. The use of generics allows us to ensure type safety and avoid unchecked casts. Another example is the Map interface, which can be used to map keys to values of any data type using generics.

Using the instanceof operator to Avoid Unchecked Casts in Java

The instanceof operator is a built-in operator in Java that is used to check whether an object is an instance of a particular class or interface. The operator returns a boolean value - true if the object is an instance of the specified class or interface, and false otherwise.

The instanceof operator is defined as follows:

where object is the object that is being checked, and class/interface is the class or interface that is being tested against.

The instanceof operator can be useful in situations where we need to perform different operations based on the type of an object. It provides a way to check the type of an object at runtime, which can help prevent errors that can occur when performing unchecked casts.

Here are some examples of using the instanceof operator:

In this example, we use the instanceof operator to check whether the object obj is an instance of the String class. If it is, we perform an explicit cast to convert the object to a String and call the toUpperCase() method on it.

In this example, we use the instanceof operator to check whether the List object passed as a parameter is an instance of the ArrayList or LinkedList classes. If it is, we perform an explicit cast to convert the List to the appropriate class and perform different operations on it depending on its type.

Overall, using the instanceof operator can help us write more robust and flexible code. However, it should be used judiciously as it can also make code harder to read and understand.

Using Polymorphism to Avoid Unchecked Casts in Java

Polymorphism is a fundamental concept in object-oriented programming. It refers to the ability of an object or method to take on multiple forms. It allows us to write code that can work with objects of different classes as long as they inherit from a common superclass or implement a common interface. This helps to reduce code duplication and makes our programs more modular and extensible.

Some of the advantages of using polymorphism are:

• Code reusability: We can write code that can work with multiple objects without having to rewrite it for each specific class.
• Flexibility: Polymorphism allows us to write code that can adapt to different types of objects at runtime.
• Ease of maintenance: By using polymorphism, changes made to a superclass or interface are automatically propagated to all its subclasses.

Here are a few examples of how you can use polymorphism to avoid unchecked casts in Java:

Example 1: Shape Hierarchy

In this example, the abstract class Shape defines the common behavior draw(), which is implemented by the concrete classes Circle and Rectangle. By using the Shape reference type, we can invoke the draw() method on different objects without the need for unchecked casts.

Example 2: Polymorphic Method Parameter

In this example, the makeAnimalSound() method accepts an Animal parameter. We can pass different Animal objects, such as Dog or Cat, without the need for unchecked casts. The appropriate implementation of the makeSound() method will be invoked based on the dynamic type of the object.

By utilizing polymorphism in these examples, we achieve type safety and avoid unchecked casts, allowing for cleaner and more flexible code.

Tips to Avoid Unchecked Casts in Java Programs

Unchecked casts in Java programs can introduce runtime errors and compromise type safety. Fortunately, there are several techniques and best practices you can employ to avoid unchecked casts and ensure a more robust codebase. Here are some effective tips to help you write Java programs that are type-safe and free from unchecked cast exceptions.

• Use generic classes, interfaces, and methods to ensure that your code handles compatible types without relying on casting.
• Embrace polymorphism by utilizing abstract classes and interfaces, define common behavior and interact with objects through their common type.
• Check the type of an object using the instanceof operator. This allows you to verify that an object is of the expected type before proceeding with the cast.
• Favor composition over inheritance, where classes contain references to other classes as instance variables.
• Familiarize yourself with design patterns that promote type safety and avoid unchecked casts. Patterns such as Factory Method, Builder, and Strategy provide alternative approaches to object creation and behavior, often eliminating the need for explicit casting.
• Clearly define the contracts and preconditions for your methods. A well-defined contract helps ensure that the method is called with appropriate types, improving overall code safety.
• Refactor your code and improve its overall design. Look for opportunities to apply the aforementioned tips, such as utilizing generics, polymorphism, or design patterns.

Unchecked casts in Java programs can introduce runtime errors and undermine type safety. By adopting practices like using generics, leveraging polymorphism, checking types with instanceof, favoring composition over inheritance, reviewing design patterns, employing design by contract, and improving code design, you can avoid unchecked casts and enhance the robustness of your Java programs. Prioritizing type safety will result in more reliable code and a smoother development process.

Lightly IDE as a Programming Learning Platform

So, you want to learn a new programming language? Don't worry, it's not like climbing Mount Everest. With Lightly IDE, you'll feel like a coding pro in no time. With Lightly IDE , you don't need to be a coding wizard to start programming.

One of its standout features is its intuitive design, which makes it easy to use even if you're a technologically challenged unicorn. With just a few clicks, you can become a programming wizard in Lightly IDE. It's like magic, but with less wands and more code.

If you're looking to dip your toes into the world of programming or just want to pretend like you know what you're doing, Lightly IDE's online Java compiler is the perfect place to start. It's like a playground for programming geniuses in the making! Even if you're a total newbie, this platform will make you feel like a coding superstar in no time.

Read more: How to Avoid Unchecked Casts in Java Programs

Top comments (0)

Templates let you quickly answer FAQs or store snippets for re-use.

Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink .

Hide child comments as well

For further actions, you may consider blocking this person and/or reporting abuse

Collaborate and Stay Ahead with NEW Forge Updates

Saurabh Karwa - Aug 16

Elevating Microsoft Teams: The Impact of Migrating from Electron to WebView2

Hamza Nadeem - Aug 16

Omprakash pandit - Aug 16

Bootstrap vs. Tailwind CSS: A Comparison of Top CSS Frameworks

dami - Aug 16

We're a place where coders share, stay up-to-date and grow their careers.

How to suppress unchecked warnings – Java

The ‘unchecked warnings’ is quite popular warning message in Java. However, if you insist this is an invalid warning, and there are no ways to solve it without compromising the existing program functionality. You may just use @SuppressWarnings(“unchecked”) to suppress unchecked warnings in Java.

1. In Class

If applied to class level, all the methods and members in this class will ignore the unchecked warnings message.

2. In Method

If applied to method level, only this method will ignore the unchecked warnings message.

3. In Property

If applied to property level, only this property will ignore the unchecked warnings message.

As conclusion, suppress an unchecked warning is like hiding a potential bug, it’s better to find the cause of the unchecked warning and fix it 🙂

Java JSON Tutorials

Parsing JSON with Jackson, Moshi, Gson etc.

About Author

import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; import java.nio.charset.Charset; import java.nio.charset.StandardCharsets; import java.nio.file.Files; import java.nio.file.Paths; import java.util.HashMap; import java.util.Iterator; import java.util.Map;

import org.json.simple.JSONArray; import org.json.simple.JSONObject; import org.json.simple.parser.JSONParser; import org.stringtemplate.v4.ST;

public class JSONDemoR3 { // Compare files\ // User File static String baseDir = “C:\\Json\\”; static String userJsonFilePath = baseDir + “UserReqest.txt”; // Kibana file static String kibanaJsonFilePath = baseDir + “kibana_mapper.txt”;

static Map mapContentUserRequestKeyValue = new HashMap();

public static void main(String args[]) throws IOException { compareJsonFile(); }

static String readKibanaMapperFile(String path, Charset encoding) throws IOException { byte[] encoded = Files.readAllBytes(Paths.get(path)); return new String(encoded, encoding); }

public static void compareJsonFile() throws IOException { // User File readSectionJson(userJsonFilePath); String content = readKibanaMapperFile(kibanaJsonFilePath, StandardCharsets.UTF_8); ST renderJson = new ST(content); for(Map.Entry map : mapContentUserRequestKeyValue.entrySet()) { renderJson.add(map.getKey(), map.getValue()); } generateUserRequestFile(renderJson.render());

private static void generateUserRequestFile(String userRequestFileJson) throws IOException { try (FileWriter file = new FileWriter(baseDir + “User_Request__” + System.currentTimeMillis() + “.json”)) { file.write(userRequestFileJson); System.out.println(“User Request Json file has been generated successfully…”); } } private static void readSectionJson(String file) { JSONParser parser = new JSONParser(); try { FileReader fileReader = new FileReader(file); JSONObject sourceJson = (JSONObject) parser.parse(fileReader); JSONArray jsonSectionArray = fetchSectionArray(sourceJson); JSONObject sectionJson = null; JSONArray fieldsJsonAry = null; @SuppressWarnings(“unchecked”) Iterator arrayIterator = jsonSectionArray.iterator(); while (arrayIterator.hasNext()) { sectionJson = (JSONObject) arrayIterator.next(); fieldsJsonAry = fetchFieldsArray(sectionJson); iteratorFields(fieldsJsonAry); }

} catch (Exception expReadJson) { expReadJson.printStackTrace(); } }

private static JSONArray fetchSectionArray(JSONObject json) { return (JSONArray) json.get(“sections”); }

private static JSONArray fetchFieldsArray(JSONObject sectionJson) { return (JSONArray) sectionJson.get(“fields”); }

private static void iteratorFields(JSONArray jsonFieldArray) { JSONObject fieldJson = null; @SuppressWarnings(“unchecked”) Iterator arrayIterator = jsonFieldArray.iterator(); while (arrayIterator.hasNext()) { fieldJson = (JSONObject) arrayIterator.next(); mapContentUserRequestKeyValue.put(fieldJson.get(“id”).toString(), fieldJson.get(“value”)); } } }

Greetings! Thanks for the solution 2 solution suited for applctn when i tried to use @SuppressWarnings(“unchecked”) it still says previous uncheked warning why!

give me more briefing on sol1 and sol2 if sol1 used any problem to the desired result? thanks in advance!

Sol1 apply to the class level, pls provide your code.

sir i am working on jdk ver 6.0 I am getting a type unchecked warning when i am compiling a code what to do to remove a error

It caused by the generic data type is undefined in your List.

Solution ..

1. Add @SuppressWarnings(“unchecked”) to ignore the checking.

2. Declare the data type for your List

Inspectopedia Help

Unchecked warning.

Reports code on which an unchecked warning will be issued by the javac compiler. Every unchecked warning may potentially trigger ClassCastException at runtime.

Locating this inspection

Can be used to locate inspection in e.g. Qodana configuration files , where you can quickly enable or disable it, or adjust its settings.

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

Settings or Preferences | Editor | Inspections | Java | Compiler issues

Inspection options

Here you can find the description of settings available for the Unchecked warning inspection, and the reference of their default values.

Not selected

Availability

IntelliJ IDEA 2024.1 , Qodana for JVM 2024.1 ,

Java, 241.18072

Stack Exchange Network

Stack Exchange network consists of 183 Q&A communities including Stack Overflow , the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

Workaround for unchecked cast of a deserialized Object to ArrayList<Vehicle>

For a class I was assigned to write code to read objects of the class Vehicle using ObjectInputStream ( in ). The objects are stored in an ArrayList called orders .

However, the compiler complains:

I always try to improve my code instead of ignoring or suppressing warnings. In this case, I have come up with a solution, but I'm trying to understand why it works, and if there is a better solution.

This update stops the warning:

Based on what I understand from what I've been reading, it works because (ArrayList<Vehicle>) obj may throw an exception if not all the elements are Vehicle . I am confused -- non-Vehicle objects can be added to the ArrayList even if its type parameter has been specified as Vehicle ? Also, is there a better solution, e.g. using instanceof ?

• serialization

• 2 \$\begingroup\$ You cannot casts a Collection with generics parameter since the at runtime the generics information is not available (due to generics erasure ) and therefore the JVM cannot check that all elements in that Collection to be of that generics type. \$\endgroup\$ –  Timothy Truckle Commented Dec 30, 2017 at 11:56

In general, the Java compiler knows the type of each variable, at every point during the execution. And when you operate on incompatible types, the program won't compile.

When you cast an object to ArrayList<Vehicle> , the Java runtime environment can only ensure that the cast to ArrayList<something> succeeds, but due to backwards compatibility (Java 1.4 from 2002), the cast will succeed, no matter if the arraylist contains Integer or String or Vehicle objects. Therefore, in this situation, the compiler warning tells you: Hey, you are doing something that cannot be checked, make sure you know what you are doing.

Your code that first deserializes the list as a raw type ( ArrayList instead of ArrayList<Vehicle> ) doesn't produce the compiler warning since the raw ArrayList is equivalent to ArrayList<Object> , and you won't get a surprising ClassCastException when working with this list.

If you are sure that the serialized list will only ever contain objects of type Vehicle , you can safely ignore that warning. In my code, I have written a utility function like this:

Another way is to not serialize the list, but to create a wrapper class:

When you serialize this class and deserialize it, you still have to cast the type using (SerializedData) in.readObject() , but the warning goes away.

This still doesn't guarantee that the vehicles list contains only vehicles after deserialization, but that is an entirely different problem.

Your Answer

Sign up or log in, post as a guest.

Required, but never shown

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy .

Not the answer you're looking for? Browse other questions tagged java serialization casting or ask your own question .

• The Overflow Blog
• Scaling systems to manage all the metadata ABOUT the data
• Navigating cities of code with Norris Numbers
• Featured on Meta
• We've made changes to our Terms of Service & Privacy Policy - July 2024
• Bringing clarity to status tag usage on meta sites

Hot Network Questions

• Clean up verbose code for Oracle SQL
• Is my encryption format secure?
• Has the application of a law ever being appealed anywhere due to the lawmakers not knowing what they were voting/ruling?
• Why is this white line between the two vertical boxes?
• Power line crossing data lines via the ground plane
• How to invoke italic correction in ConTeXt LMTX?
• Is the Ted-Ed Leprechaun's Magic Bag Unique?
• Why would Space Colonies even want to secede?
• Non-linear recurrence for rational sequences with generating function with radicals?
• Can I cast True Strike, then cast Message to give someone else advantage?
• Repeats: Simpler at the cost of more redundant?
• Unexpected behaviour during implicit conversion in C
• If Venus had a sapient civilisation similar to our own prior to global resurfacing, would we know it?
• Will the US Customs be suspicious of my luggage if i bought a lot of the same item?
• DIN Rail Logic Gate
• Does the First Amendment protect deliberately publicizing the incorrect date for an election?
• Advice needed: Team needs developers, but company isn't posting jobs
• Cover letter format in Germany
• Stargate "instructional" videos
• What is the airspeed record for a helicopter flying backwards?
• Output of a Diffractometer
• How to satisfy the invitation letter requirement for Spain when the final destination is not Spain
• Can I use the Chi-square statistic to evaluate theoretical PDFs against an empirical dataset of 60,000 values?
• What is a word/phrase that best describes a "blatant disregard or neglect" for something, but with the connotation of that they should have known?

• Password Generator
• HTML Editor
• HTML Encoder
• JSON Beautifier
• CSS Beautifier
• Markdown Convertor
• Find the Closest Tailwind CSS Color
• Phrase encrypt / decrypt
• Browser Feature Detection
• Number convertor
• CSS Maker text shadow
• CSS Maker Text Rotation
• CSS Maker Out Line
• CSS Maker RGB Shadow
• CSS Maker Transform
• CSS Maker Font Face
• Color Picker
• Colors CMYK
• Color mixer
• Color Converter
• Color Contrast Analyzer
• Color Gradient
• String Length Calculator
• MD5 Hash Generator
• Sha256 Hash Generator
• String Reverse
• URL Encoder
• URL Decoder
• Base 64 Encoder
• Base 64 Decoder
• Extra Spaces Remover
• String to Lowercase
• String to Uppercase
• Word Count Calculator
• Empty Lines Remover
• HTML Tags Remover
• Binary to Hex
• Hex to Binary
• Rot13 Transform on a String
• String to Binary
• Duplicate Lines Remover

What is SuppressWarnings ("unchecked") in Java?

@SuppressWarnings("unchecked") is an annotation in Java that tells the compiler to suppress specific warnings that are generated during the compilation of the code.

The unchecked warning is issued by the compiler when a type safety check has been suppressed, typically using an @SuppressWarnings("unchecked") annotation or by using a raw type in a parameterized type.

For example, consider the following code:

In this example, the compiler will issue an unchecked warning because the elements of the list are not checked for type safety when they are added to the list2 variable. The @SuppressWarnings("unchecked") annotation is used to suppress this warning.

The @SuppressWarnings annotation should be used with caution, as it can mask potential problems in the code. It is generally a good idea to fix the underlying issue that is causing the warning, rather than suppressing the warning.

Related Resources

• Is Java "pass-by-reference" or "pass-by-value"?
• How do I read / convert an InputStream into a String in Java?
• Avoiding NullPointerException in Java
• What are the differences between a HashMap and a Hashtable in Java?
• What is the difference between public, protected, package-private and private in Java?
• What is a JavaBean exactly?
• What does "Could not find or load main class" mean?
• What does 'synchronized' mean?
• HTML Basics
• Javascript Basics
• TypeScript Basics
• React Basics
• Angular Basics
• Sass Basics
• Vue.js Basics
• Python Basics
• Java Basics
• NodeJS Basics

Generics unchecked assignment

SCJP 1.4 - SCJP 6 - SCWCD 5 - OCEEJBD 6 - OCEJPAD 6 How To Ask Questions How To Answer Questions

Java @SuppressWarnings Annotation

Last updated: January 8, 2024

• Java Annotations

Java applications have a notoriously slow startup and a long warmup time. The CRaC (Coordinated Restore at Checkpoint) project from OpenJDK can help improve these issues by creating a checkpoint with an application's peak performance and restoring an instance of the JVM to that point.

To take full advantage of this feature, BellSoft provides containers that are highly optimized for Java applications. These package Alpaquita Linux (a full-featured OS optimized for Java and cloud environment) and Liberica JDK (an open-source Java runtime based on OpenJDK).

These ready-to-use images allow us to easily integrate CRaC in a Spring Boot application:

Improve Java application performance with CRaC support

Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, you can get started over on the documentation page .

And, you can also ask questions and leave feedback on the Azure Container Apps GitHub page .

Whether you're just starting out or have years of experience, Spring Boot is obviously a great choice for building a web application.

Jmix builds on this highly powerful and mature Boot stack, allowing devs to build and deliver full-stack web applications without having to code the frontend. Quite flexibly as well, from simple web GUI CRUD applications to complex enterprise solutions.

Concretely, The Jmix Platform includes a framework built on top of Spring Boot, JPA, and Vaadin , and comes with Jmix Studio, an IntelliJ IDEA plugin equipped with a suite of developer productivity tools.

The platform comes with interconnected out-of-the-box add-ons for report generation, BPM, maps, instant web app generation from a DB, and quite a bit more:

>> Become an efficient full-stack developer with Jmix

DbSchema is a super-flexible database designer, which can take you from designing the DB with your team all the way to safely deploying the schema .

The way it does all of that is by using a design model , a database-independent image of the schema, which can be shared in a team using GIT and compared or deployed on to any database.

And, of course, it can be heavily visual, allowing you to interact with the database using diagrams, visually compose queries, explore the data, generate random data, import data or build HTML5 database reports.

>> Take a look at DBSchema

Get non-trivial analysis (and trivial, too!) suggested right inside your IDE or Git platform so you can code smart, create more value, and stay confident when you push.

Get CodiumAI for free and become part of a community of over 280,000 developers who are already experiencing improved and quicker coding.

Write code that works the way you meant it to:

>> CodiumAI. Meaningful Code Tests for Busy Devs

The AI Assistant to boost Boost your productivity writing unit tests - Machinet AI .

AI is all the rage these days, but for very good reason. The highly practical coding companion, you'll get the power of AI-assisted coding and automated unit test generation . Machinet's Unit Test AI Agent utilizes your own project context to create meaningful unit tests that intelligently aligns with the behavior of the code. And, the AI Chat crafts code and fixes errors with ease, like a helpful sidekick.

Simplify Your Coding Journey with Machinet AI :

>> Install Machinet AI in your IntelliJ

Do JSON right with Jackson

Download the E-book

Get the most out of the Apache HTTP Client

Get Started with Apache Maven:

Working on getting your persistence layer right with Spring?

Explore the eBook

Building a REST API with Spring?

Get started with Spring and Spring Boot, through the Learn Spring course:

Explore Spring Boot 3 and Spring 6 in-depth through building a full REST API with the framework:

>> The New “REST With Spring Boot”

Get started with Spring and Spring Boot, through the reference Learn Spring course:

>> LEARN SPRING

Yes, Spring Security can be complex, from the more advanced functionality within the Core to the deep OAuth support in the framework.

I built the security material as two full courses - Core and OAuth , to get practical with these more complex scenarios. We explore when and how to use each feature and code through it on the backing project .

You can explore the course here:

>> Learn Spring Security

Spring Data JPA is a great way to handle the complexity of JPA with the powerful simplicity of Spring Boot .

Get started with Spring Data JPA through the guided reference course:

>> CHECK OUT THE COURSE

1. Overview

In this quick tutorial, we’ll have a look at how to use the @SuppressWarnings annotation.

2. @SuppressWarnings  Annotation

Compiler warning messages are usually helpful. Sometimes warnings can get noisy, though.

Especially when we can’t or don’t want to address them:

The compiler will issue a warning about this method. It’ll warn that we’re using a raw-typed collection. If we don’t want to fix the warning, then we can suppress it with the @SuppressWarnings annotation .

This annotation allows us to say which kinds of warnings to ignore. While warning types can vary by compiler vendor , the two most common are deprecation and unchecked .

deprecatio n tells the compiler to ignore when we’re using a deprecated method or type.

unchecked tells the compiler to ignore when we’re using raw types.

So, in our example above, we can suppress the warning associated with our raw type usage :

To suppress a list of multiple warnings, we set a String array containing the corresponding warning list:

3. Conclusion

In this guide, we saw how we can use the  @SuppressWarnings annotation in Java.

The full source code for the examples can be found over on GitHub .

Looking for the ideal Linux distro for running modern Spring apps in the cloud?

Meet Alpaquita Linux : lightweight, secure, and powerful enough to handle heavy workloads.

This distro is specifically designed for running Java apps . It builds upon Alpine and features significant enhancements to excel in high-density container environments while meeting enterprise-grade security standards.

Specifically, the container image size is ~30% smaller than standard options, and it consumes up to 30% less RAM:

>> Try Alpaquita Containers now.

Explore the secure, reliable, and high-performance Test Execution Cloud built for scale. Right in your IDE:

Basically, write code that works the way you meant it to.

AI is all the rage these days, but for very good reason. The highly practical coding companion, you'll get the power of AI-assisted coding and automated unit test generation . Machinet's Unit Test AI Agent utilizes your own project context to create meaningful unit tests that intelligently aligns with the behavior of the code.

How to fix this unchecked assignment warning?

I got Warning:(31, 46) Unchecked assignment: 'java.lang.Class' to 'java.lang.Class<? extends PACKAGE_NAME.Block>' warning on the line blockRta.registerSubtype(c); , but I can’t figure out how to fix that without supressing it.

ReflectionHelper.getClasses is a static method to get all the classes in that package name, and its return type is Class[] . Block is an interface. RuntimeTypeAdapterFactory is a class in gson extra, and its source code can be viewed here .

Advertisement

Since ReflectionHelper.getClasses returns an array of the raw type Class , the local-variable type inference will use this raw type Class[] for var blks and in turn, the raw type Class for var c . Using the raw type Class for c allows passing it to registerSubtype(Class<? extends Block>) , without any check, but not without any warning. You can use the method asSubclass to perform a checked conversion, but you have to declare an explicit non-raw variable type, to get rid of the raw type, as otherwise, even the result of the asSubclass invocation will be erased to a raw type by the compiler.

There are two approaches. Change the type of blks :

Then, the type of var c changes automatically to Class<?> .

Or just change the type of c :

Unchecked Assignment in java

I'm using the following code to find a one-dimensional list of unique objects in an n-dimensional list (credits to someone on StackOverflow a while ago for the approach):

It works but I am still getting an 'unchecked assignment' warning when casting listitem to List in the following line listitem 为 List 时，我仍然收到“未检查分配”警告-->

Now I know I could just add @SuppressWarnings("unchecked") and it would hide the warning. @SuppressWarnings("unchecked") 并且它会隐藏警告。--> But is there a fundamentally different approach to doing this without this warning? Does it even matter in the end at all if this warning is there? Can fundamentally good code still contain warnings?

solution1  1 ACCPTED  2018-03-04 11:34:56

I don't see a way to get rid of that warning, as you you have to be very careful to declare and use the correct generic array types. So maybe you decide to ignore the warning...

• A 1-dimensional array with elements of type T are correctly described by your List<T> declaration. List<T> 声明正确描述了具有 T 类型元素的一维数组。-->
• A 2-dimensional array is a list, containing lists of elements, so that should be List<List<T>> . List<List<T>> 。-->
• A 3-dimensional array is a list, containing lists of lists elements, so that should be List<List<List<T>>> . List<List<List<T>>> 。-->

The very core of your search is the recursive getUniqueObjectsInArray(...) method. getUniqueObjectsInArray(...) 方法。--> To get rid of the warning, you'd have to make sure that a call with eg List<List<List<String>>> produces a recursive (inner) call with List<List<String>> , and a dimension one less than before, so a first attempt would be something like: List<List<List<String>>> 的调用会产生一个带有 List<List<String>> 的递归（内部）调用，并且维度减少一比以前，所以第一次尝试将是这样的：-->

That also won't work, as the compiler won't allow you to do the recursive call, as he can't make sure that the listItem is a List. Let's try to tell him that by:

Now he knows that it's a list, but now that isn't enough, as now you need a List<List<whatever>> for calling getUniqueObjectsInArray(...) . List<List<whatever>> 来调用 getUniqueObjectsInArray(...) 。-->

You see, the attempts to do the right generics declaration so that the compiler doesn't warn, become quite complex, if at all possible. Honestly, I don't see a way to avoid the warnings, so don't spend too much time, and add @SuppressWarnings("unchecked").

solution2  0  2018-03-04 11:03:04

Well, I do not see the way to get rid of this warning since you perform down casting Object to List . Object to List 。-->

In your case the item in the list either could be some object or list , and you don't have generics support or other language construct that could describe this fact. 可以是某个 object 或 list ，并且您没有泛型支持或可以描述此事实的其他语言构造。-->

So as I see it at some point you need to perform casting operation.

The difference though is that what you have now is not safe: how exactly are you ensuring that here

that listItem is a subtype of a List ? listItem 是 List 的子类型？-->

What you can do is to try to bound you generic type and/or perform instance of checks to ensure correctness of the casting. instance of 以确保转换的正确性。-->

solution3  0  2018-03-04 11:24:49

You're implicitly casting all of your items in your list.

This example will compile without a warning because I am not casting the objects in the list to anything beside Object. If I switch ? ? --> to Integer , then I get a warning. Integer ，然后我收到警告。-->

solution4  -1  2018-03-04 10:10:10

This is because you are casting the object "listItem" to "List" without generic type parameters.

To get rid of this, just add the generic type parameters into the cast and it should get rid of the warning

• Related Question
• Related Blog
• Related Tutorials

The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:[email protected].

• intellij-idea
• executorservice
• type-erasure
• uncaught-exception
• multithreading

Annotation Interface SuppressWarnings

As a matter of style, programmers should always use this annotation on the most deeply nested element where it is effective. If you want to suppress a warning in a particular method, you should annotate that method rather than its class.

Required Element Summary

Element details.

The string "unchecked" is used to suppress unchecked warnings. Compiler vendors should document the additional warning names they support in conjunction with this annotation type. They are encouraged to cooperate to ensure that the same names work across multiple compilers.

Scripting on this page tracks web page traffic, but does not change the content in any way.

An official website of the United States government

Here’s how you know

Official websites use .gov A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS A lock ( Lock A locked padlock ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Free Cyber Services #protect2024 Secure Our World Shields Up Report A Cyber Issue

Vulnerability Summary for the Week of August 5, 2024

The CISA Vulnerability Bulletin provides a summary of new vulnerabilities that have been recorded by the  National Institute of Standards and Technology  (NIST)  National Vulnerability Database  (NVD) in the past week. In some cases, the vulnerabilities in the bulletin may not yet have assigned CVSS scores. Please visit NVD for updated vulnerability entries, which include CVSS scores once they are available.

Vulnerabilities are based on the  Common Vulnerabilities and Exposures  (CVE) vulnerability naming standard and are organized according to severity, determined by the  Common Vulnerability Scoring System  (CVSS) standard. The division of high, medium, and low severities correspond to the following scores:

• High : vulnerabilities with a CVSS base score of 7.0–10.0
• Medium : vulnerabilities with a CVSS base score of 4.0–6.9
• Low : vulnerabilities with a CVSS base score of 0.0–3.9

Entries may include additional information provided by organizations and efforts sponsored by CISA. This information may include identifying information, values, definitions, and related links. Patch information is provided when available. Please note that some of the information in the bulletin is compiled from external, open-source reports and is not a direct result of CISA analysis.  

High Vulnerabilities

Back to top

Medium Vulnerabilities

Low Vulnerabilities

Severity Not Yet Assigned

Please share your thoughts

We recently updated our anonymous product survey ; we’d welcome your feedback.

Warning: What you are about to hear from Trump are lies

The tendency for many in my industry to let the vast majority of donald trump’s harmful false statements go unchecked — it’s just trump being trump — presents a persistent and growing danger..

In Donald Trump’s rambling, hourlong media spectacle last week, he delivered an ominous warning about Governor Tim Walz of Minnesota, the running mate of Trump’s presidential rival, Vice President Kamala Harris.

“He’s going for things that nobody’s ever even heard of,” Trump said of Walz . “Heavy into the transgender world. Heavy into lots of different worlds.”

Per his usual style, Trump cited no facts, examples, or other specifics to support his claim. Perhaps the vagueness of Trump’s attack, coupled with the fact that it was among the more than 160 lies or misrepresentations Trump uttered in the course of the hour, made it nearly impossible for journalists to adequately question, let alone challenge and fact-check, him in real time.

But that didn’t make his hatemongering any less perilous. In fact, the tendency for many people in my industry to let the vast majority of harmful false statements that come out the former president’s mouth go unchecked — it’s just Trump being Trump — presents a persistent and growing danger.

Not everyone watching that so-called press conference knew that Walz signed a bill that protects Minnesotans’ access to gender-affirming care and stopped minors who received such care from being removed from their homes by state officials. They were not told he also enacted a law that provides free menstruation products in public school restrooms — available to everyone who may need them, including girls and transgender boys. Yes, NPR provided a helpful itemized debunking of Trump’s lies — but it was published three days later. That nuance was lost in the moment, but the hatemongering was allowed to land unobstructed.

Advertisement

What’s the harm in that? According to a growing body of research, a lot.

The stigmatization of transgender people has devastating consequences. Studies show that the discrimination, prejudice, and bias against transgender people not only make them more likely to be denied employment and other opportunities but lead to low self-esteem and poor physical and psychological health outcomes. Transgender people are more likely to have eating disorders or attempt suicide. Transgender individuals are four times as likely to be victims of violent crime , including hate crimes and murder, than cisgender Americans.

Usually, when news outlets air potentially dangerous, harmful, or disturbing content, viewers get a heads-up. They’re told, “this footage may be difficult to watch,” or “the following footage depicts a violent scene. Viewer discretion is advised.”

Where was the warning about Trump, who has a decades-long history of bald-faced lying, threatening members of the press, pushing dangerous conspiracy theories, and spewing hate?

Trump is the GOP presidential nominee so his statements should not be hidden from voters. Far from it — Americans must see and hear what he says to make an informed decision at the polls.

But if news networks insist on abdicating their duty to fact-check their content before it airs, then it’s time for them to give viewers a clear warning before carrying any part of a Trump news appearance or campaign rally live. Thursday’s scheduled “press conference” at Trump’s Bedminster, N.J., golf club is a perfect opportunity.

Might I suggest: “Donald Trump has a documented history of lying at events like the one we are about to show you. We will do our best to fact-check his claims as soon as we are able, but in the meantime, consider his statements with care.”

Last week’s press event is replete with examples of the fact-free dangerous language that deserves a warning, like Trump’s false assertion that rampant violent crime has put the nation “in the most dangerous position it’s ever been in … from a safety standpoint.”

In fact, violent crime has dropped precipitously in most American cities since a pandemic-era surge, according to data from the Major Cities Chiefs Association .

But Trump’s false alarm has very real potential consequences: Project 2025 , which Trump claims ignorance of but which was compiled by his former staffers and current backers, includes a plan to allow federal officials to backseat-drive local law enforcement and prosecutions , empowering the Justice Department to step in with federal law enforcement, increased federal prosecutions, and even disciplinary action against local police chiefs and prosecutors if they are not deemed tough enough on this nonexistent crime wave. And efforts to tackle racial disparities in policing and prosecutions are explicitly cited as a target of the next GOP-led Justice Department’s ire. But again — viewers of Trump’s event learned none of this in real time.

Of course, news outlets should be fact-checking all political candidates vigorously, including Harris and Walz. But neither of those candidates have the record of constantly spewing the dangerous misinformation that Trump has. News networks would never put out content that declares cigarette or asbestos to be safe. They are quick to warn of potential health risks like listeria outbreaks or storm surges. They won’t even show a high-speed car chase without a delay, giving them time to prevent a horrific scene from going across their airwaves and cable lines.

They should use that same energy on Trump.

Kimberly Atkins Stohr is a columnist for the Globe. She may be reached at [email protected] . Follow her @KimberlyEAtkins .

Globe Opinion

• Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers
• Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand
• OverflowAI GenAI features for Teams
• OverflowAPI Train & fine-tune LLMs
• Labs The future of collective knowledge sharing
• About the company Visit the blog

Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

Get early access and see previews of new features.

Unchecked assignment: 'java.util.List' to 'java.util.Collection<? extends manu.apps.lucemtrader.classes.Investor>'

I am having an adapter where i have two lists one list is for InvestorsList where it comes with the list of investors and the other list is called investorListFull which is used to filter results when searching.

Below is how i have declared the lists

Below is how the lists are assigned in my recyclerview adapter constructor

Below is how i am filtering results in investors list

I am getting Unchecked assignment error in publish results investorList.addAll((List) filterResults.values);

• android-studio

I am getting Unchecked cast error in publish results investorList.addAll((List) filterResults.values);

That's because you're doing an unchecked cast. Actually, you're doing both a checked and an unchecked cast there.

(List) filterResults.values is a checked cast. This means that the Java compiler will insert a checkcast instruction into the bytecode to ensure that filterResults.values (an Object ) really is an instance of List .

However, investorList.addAll expects a List<Investor> , not a List . List is a raw type . You can pass a raw-typed List to a method expecting a List<Something> ; but this is flagged as unsafe because the compiler can't guarantee that it really is a List<Something> - there is nothing about the List that makes it a "list of Something ", because of type erasure. The compiler can insert a checkcast instruction to ensure it's a List ; but not one to ensure it's a List<Something> : this fact is unchecked .

What it's saying with the warning is "there may be something wrong here; I just can't prove it's wrong". If you know for sure - by construction - that filterResults.values really is a List<Investor> , casting it to List<Investor> is safe.

You should write the line as:

Note that this will still give you an unchecked cast warning, because it's still an unchecked cast - you just avoid the use of raw types as well.

If you feel confident in suppressing the warning, declare a variable, so you can suppress the warning specifically on that variable, rather than having to add the suppression to the method or class; and document why it's safe to suppress there:

• @SuppressWarnings("unchecked") causes an issue in sonar. I wonder if there is a way to get rid of both warnings... –  andy Commented Aug 23, 2022 at 15:24

Your Answer

Reminder: Answers generated by artificial intelligence tools are not allowed on Stack Overflow. Learn more

Sign up or log in

Post as a guest.

Required, but never shown

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy .

Not the answer you're looking for? Browse other questions tagged java android android-studio arraylist or ask your own question .

• The Overflow Blog
• Scaling systems to manage all the metadata ABOUT the data
• Navigating cities of code with Norris Numbers
• Featured on Meta
• We've made changes to our Terms of Service & Privacy Policy - July 2024
• Bringing clarity to status tag usage on meta sites
• Feedback requested: How do you use tag hover descriptions for curating and do...

Hot Network Questions

• Unexpected behaviour during implicit conversion in C
• What was the reason for not personifying God's spirit in NABRE's translation of John 14:17?
• Why HIMEM was implemented as a DOS driver and not a TSR
• Did the Space Shuttle weigh itself before deorbit?
• Are all simple groups of order coprime to 3 cyclic? If so, why?
• Trace operation as contraction - how can we contract only contravariant indices?
• Three 7-letter words, 21 unique letters, excludes either HM or QS
• What does it mean to have a truth value of a 'nothing' type instance?
• Can I use the Chi-square statistic to evaluate theoretical PDFs against an empirical dataset of 60,000 values?
• How to handle stealth before combat starts?
• Prove that there's a consecutive sequence of days during which I took exactly 11 pills
• Erase the loops
• Is there a "simplest" way to embed a graph in 3-space?
• How predictable are the voting records of members of the US legislative branch?
• How can I expose paragraph type third_party_settings and other properties on JSON:API?
• Violation of the Law of Total Expectation in the Unit Square?
• Is there any point "clean-installing" on a brand-new MacBook?
• Many and Many of - a subtle difference in meaning?
• How to read data from Philips P2000C over its serial port to a modern computer?
• What majority age is taken into consideration when travelling from country to country?
• Venus’ LIP period starts today, can we save the Venusians?
• Who became an oligarch after the collapse of the USSR
• Were there mistakes in converting Dijkstra's Algol-60 compiler to Pascal?
• What's wrong with my app authentication scheme?