java mock unchecked assignment

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Using Mockito to mock classes with generic parameters

Is there a clean method of mocking a class with generic parameters? Say I have to mock a class Foo<T> which I need to pass into a method that expects a Foo<Bar> . I can do the following easily enough:

Assuming getValue() returns the generic type T . But that's going to have kittens when I later pass it into a method expecting Foo<Bar> . Is casting the only means of doing this?

• 3 Why use foo and bar over more meaningful names. Just created a whole load of confusion for a lot of people. –  Kaigo Commented Jul 25, 2020 at 20:26
• 13 @Kaigo it's quite typical in programming examples to use foo, bar and baz, especially when anonymizing real-world examples to hide confidential details. now, I'm more concerned with the fact that OP used the phrase "that's going to have kittens"...literally never heard anyone say that before ;) –  Adam Burley Commented Mar 13, 2021 at 14:04
• Everyone knows that "having kittens" is bad thing for code to be doing, even if it's pretty great for cats. :--) –  Charlie Reitzel Commented Jan 29, 2022 at 18:12

12 Answers 12

I think you do need to cast it, but it shouldn't be too bad:

• 55 Yes but you still have a warning. Is that possible to avoid the warning? –  odwl Commented Aug 31, 2010 at 19:11
• 25 @SuppressWarnings("unchecked") –  qualidafial Commented Dec 10, 2010 at 1:13
• 30 I think this is fully acceptable since we are talking about a mock object in a unit test. –  Magnilex Commented Nov 26, 2014 at 13:06
• 1 @demaniak It doesn't work at all. Argument matchers can't be used in that context. –  Krzysztof Krasoń Commented May 19, 2018 at 20:53
• 2 @demaniak That will compile just fine, but when running the test it will throw InvalidUseOfMatchersException (which is a RuntimeException) –  Superole Commented Jun 4, 2018 at 12:32

One other way around this is to use @Mock annotation instead. Doesn't work in all cases, but looks much sexier :)

Here's an example:

The MockitoJUnitRunner initializes the fields annotated with @Mock .

• 3 this is deprecated in 1.9.5. :( Seems much cleaner to me. –  Pure Function Commented Mar 27, 2014 at 21:36
• 18 @CodeNovitiate I couldn't find any deprecation annotations on MockitoJUnitRunner and Mock in 1.9.5. So, what is deprecated? (Yes, org.mockito.MockitoAnnotations.Mock is deprecated, but you should use org.mockito.Mock instead) –  neu242 Commented May 22, 2014 at 7:31
• 17 Well done, this worked perfectly for me. It's not just "sexier", it avoids a warning without using SuppressWarnings . Warnings exist for a reason, it's better to not be in the habit of suppressing them. Thanks! –  Nicole Commented Jun 3, 2014 at 17:43
• 5 There is one thing I don't like about using @Mock instead of mock() : the fields are still null during construction time, so I cannot insert dependencies at that time and cannot make the fields final. The former can be solved by a @Before -annotated method of course. –  Rüdiger Schulz Commented Sep 25, 2014 at 9:26
• 4 For initiation just call MockitoAnnotations.initMocks(this); –  borjab Commented Apr 6, 2016 at 12:31

You could always create an intermediate class/interface that would satisfy the generic type that you are wanting to specify. For example, if Foo was an interface, you could create the following interface in your test class.

In situations where Foo is a non-final class, you could just extend the class with the following code and do the same thing:

Then you could consume either of the above examples with the following code:

• 4 Provided Foo is an interface or non-final class, this appears to be a reasonably elegant solution. Thanks. –  Tim Clemons Commented Apr 29, 2014 at 15:39
• I updated the answer to include examples for non-final classes as well. Ideally you would be coding against an interface, but that's not always going to be the case. Good catch! –  dsingleton Commented Apr 30, 2014 at 15:15

Create a test utility method . Specially useful if you need it for more than once.

• Could extend your answer to make a general utility method passing in the class you want to mock. –  William Jarvis Commented Feb 5, 2016 at 10:19
• 2 @WilliamDutton static <T> T genericMock(Class<? super T> classToMock) { return (T)mock(classToMock); } it doesn't even need a single suppression :) But be careful, Integer num = genericMock(Number.class) compiles, but throws ClassCastException . This is only useful for the most common G<P> mock = mock(G.class) case. –  TWiStErRob Commented Jul 13, 2016 at 12:06

I agree that one shouldn't suppress warnings in classes or methods as one could overlook other, accidentally suppressed warnings. But IMHO it's absolutely reasonable to suppress a warning that affects only a single line of code.

• 1 Sorry to necro this post, but I've never seen annotations on a statement like this in Java, and the docs don't say anything about it either. Am I missing something? –  Rabadash8820 Commented Aug 12, 2022 at 16:30
• 1 @Rabadash8820 "Annotations can be applied to declarations: declarations of classes, fields, methods, and other program elements. When used on a declaration, each annotation often appears, by convention, on its own line." The reason the examples don't show that is because they're demonstrating new uses of annotations from Java 8 on that page. See the JLS (Java Language Standard) for specifics. docs.oracle.com/javase/specs/jls/se21/html/jls-9.html#jls-9.7.4 –  Captain Man Commented Jun 29 at 3:21

With JUnit5 I think the best way is to @ExtendWith(MockitoExtension.class) with @Mock in the method parameter or the field.

The following example demonstrates that with Hamcrest matchers.

See https://www.vogella.com/tutorials/Mockito/article.html for the required Maven/Gradle dependencies.

As the other answers mentioned, there's not a great way to use the mock() & spy() methods directly without unsafe generics access and/or suppressing generics warnings.

There is currently an open issue in the Mockito project ( #1531 ) to add support for using the mock() & spy() methods without generics warnings. The issue was opened in November 2018, but there aren't any indications that it will be prioritized. Per one of the Mockito contributor's comments on the issue:

Given that .class does not play well with generics, I don't think there is any solution we can do in Mockito. You can already do @Mock (the JUnit5 extension also allows method parameter @Mock s) and that should be a suitable alternative. Therefore, we can keep this issue open, but it is unlikely ever to be fixed, given that @Mock is a better API.

• 1 For some cases spy() is alright, because you can pass an instance to it. Obviously doesn't cover all your bases but if you can instantiate a generic instance you're good to go. –  xbakesx Commented Sep 28, 2020 at 22:01

JUnit5 : use @ExtendWith(MockitoExtension.class) on the test class then add this field:

• This solution is already detailed in several other answers, I'm unsure how it adds any value. –  Pyves Commented Jun 7, 2021 at 8:33
• @Pyves this covers JUnit5 which does not work with @RunWith(MockitoJUnitRunner.class) –  xilef Commented Jun 9, 2021 at 8:09
• I am seeing at least one other answer that already covered @ExtendWith(MockitoExtension.class) , and other answers that work regardless of the version of JUnit in use. This isn't really the key point of the question/answer anyway. –  Pyves Commented Jun 9, 2021 at 8:18

So you have this:

Ways to fix it, starting from my least favourite to most:

• Use @SuppressWarnings("unchecked") annotation. Doesn't really fix it, but you'll stop getting the warnings.
• Cast it. Though it still gives warnings, unfortunately. So you need to use the annotation here as well:
• Use @Mock annotation. There will be no warnings. Here, when can be added in actual tests.
• Use @MockBean annotation. This will create a mocked bean directly. No warnings.

Here is an interesting case: method receieves generic collection and returns generic collection of same base type. For example:

This method can be mocked with combination of Mockito anyCollectionOf matcher and the Answer.

The (in my opinion) most easiest and most readable approach is to use method level injection.

This will result in having all test data within the test method. This will keep your test classes clean as there are no 'floating' mock's.

why not using spy

• 2 This will still lead to warnings,as highlighted by other answers. –  Pyves Commented Jun 7, 2021 at 8:32

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Using @Mock as a Method Parameter with Mockito

As with many other Java developers, I heavily utilise Mockito as a mocking framework for unit testing.

I'll often end up with tests that look like this:

In this case, I want to create a List and check it's returned by the caching layer I'm testing.

However, this is a good example of where inlining our mock calls is bad, because IntelliJ warns us:

This is quite annoying, and pollutes our codebase with warnings that we really want to avoid.

One solution would be to make it a field of the test class, and @Mock it there, but in this case it's a throwaway mock that is only required in this test, not in all tests (therefore wouldn't make as much sense to make a field variable).

Fortunately, we can utilise something my colleague Lewis taught me the other week, and use @Mock as a method parameter when using JUnit5.

This gives us the following test:

This would of course, make our tests more readable if we had many mocks being set up!

Note that you also need to make sure you're using Mockito's mock setup:

This has been tested as of spring-boot-starter-test v2.2.4.RELEASE, and works in Mockito 2+ with JUnit5+.

I have raised a PR to add it to the Mockito 3.x documentation , but not 2.x as per request of the Mockito core team .

This post's permalink is https://www.jvt.me/posts/2020/06/27/mockito-mock-parameter/ and has the following summary:

Using `@Mock` on method parameters to reduce manual mock setups with Mockito.

The canonical URL for this post is https://www.jvt.me/posts/2020/06/27/mockito-mock-parameter/ .

Content for this article is shared under the terms of the Creative Commons Attribution Non Commercial Share Alike 4.0 International , and code is shared under the Apache License 2.0 .

# blogumentation # java # mockito .

This post was filed under articles .

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How to use mockito to mock a generic class.

This article will explore how to use the Mockito library to mock a generic class in Java. We will start by explaining what Mockito is and how to use it. Then we will explore the @Mock annotation in Java for mock tests . After that, we will delve into the particulars of using Mockito in a generic class. Finally, we will list the advantages and disadvantages of using a library like Mockito in Java.

Let's jump right in.

What Is Mockito?

Mockito is a popular Java library that allows you to create mock objects for testing purposes . Mocking is a technique that lets you replace the functionality of an object or class with a simulated version, which can help test how your code interacts with other components.

To mock a generic class with Mockito, you'll need to do the following:

Create a mock object of the generic class using the Mockito.mock() method.

Set up the desired behavior of the mock object using Mockito's when() and thenReturn() methods.

This will cause the mock object to return "Hello, world!" whenever the getValue() method is called.

Use the mock object in your test code like any other object.

Verify that the mock object was used as expected using the Mockito.verify() method.

This will ensure that the getValue() method is called exactly once on the mock object.

Using the @Mock Annotation

The @Mock annotation is a convenient way to create mock objects in Mockito. It allows you to create and inject mock objects into your test classes without manually calling the Mockito.mock() method.

To use the @Mock annotation, you'll need to do the following:

Annotate a field in your test class with @Mock .

This will create a mock object of the specified type and assign it to the field.

Initialize the mock objects in your test class using the MockitoAnnotations.initMocks() method.

This will initialize all fields in your test class annotated with @Mock and assign them their corresponding mock objects.

Use the mock object in your test methods as you would any other object.

The @Mock annotation is a convenient way to create and manage mock objects in your tests and can save you time and boilerplate code when setting up mock objects.

Keep in mind that the @Mock annotation only creates mock objects. It does not set up their behavior. So you'll still need to use the when() and thenReturn() methods or another method of specifying the mock object's behavior, such as the Answer interface or a custom Answer implementation.

Using Mockito on a Generic Class

Using Mockito to mock a generic class can be more complicated than mocking a regular class due to the added complexity of generics. However, with a bit of practice and an understanding of how Mockito works, you should be able to use it to mock generic classes in your tests effectively.

One important thing to keep in mind when mocking generic classes is that Mockito's mock() method uses type erasure to create the mock object. This means that the type information of the generic class is not preserved at runtime, which can cause issues if you try to use the mock object in a way that relies on the specific type parameters of the class.

For example, consider the following generic class:

If you create a mock object of this class using Mockito's mock() method, Mockito will replace the type parameter T with the type Object at runtime. Unfortunately, if you try to call a method on the mock object that takes an argument of type T , you'll get a compile-time error because the mock object doesn't have a corresponding method that takes an Object argument.

To work around this issue, you can use Mockito's @Captor annotation to create an ArgumentCaptor object that can capture the arguments passed to the mock object's methods. You can then use the ArgumentCaptor to access the captured arguments and verify that they have the expected type.

For example:

This code sets up the mock object to return true whenever the setValue() method is called with any argument and then verifies that the setValue() method was called with the correct argument using the ArgumentCaptor .

Mocking Using the Answer Interface

Another option for mocking generic classes is to use Mockito's Answer interface, which allows you to specify a custom behavior for the mock object's methods. This can be useful if you need to perform more complex operations or use the type information of the generic class in your mock object's behavior.

This code sets up the mock object to return the argument passed to the getValue() method as the return value.

To use the Answer interface, you'll need to create a new implementation of the Answer interface and override the answer() method. The answer() method takes an InvocationOnMock object as an argument, representing the method call made on the mock object. You can use the InvocationOnMock object to access the arguments passed to the method and perform any desired operations.

Here's an example of how you might use the Answer interface to mock a generic class:

You can then use this Answer implementation to set up the desired behavior of your mock object like this:

This will cause the mock object to return the transformed argument whenever the getValue() method is called.

Mockito's Advantages and Disadvantages

Here are some advantages of using Mockito:

• It's easy to use. Mockito has a simple and intuitive API that makes it easy to create and use mock objects in your tests.
• It's widely used. Mockito is a popular library with a large user base, which means it's well tested and has a wealth of documentation and resources available.
• It integrates well with other tools. Mockito works well with other testing tools and libraries, such as JUnit and PowerMock.
• It supports a variety of mock object types. Mockito allows you to create mock objects of various types, including regular classes, interfaces, and final classes.

Some potential disadvantages of using Mockito include the following:

• Mocking generic classes: As mentioned earlier, Mockito's mock() method uses type erasure, making it difficult to mock generic classes in a way that preserves their type information.
• Mocking final classes and methods: Mockito cannot mock final classes or methods, which can be a limitation if you need to test code that relies on these classes or methods.
• Mocking static methods: Mockito does not directly support the mocking of static methods, although this can be done using the PowerMock library in combination with Mockito.
• Mocking complex behavior: While Mockito is good at mocking simple behavior, it can be more challenging to mock complex or nuanced behavior, which may require more manual setup or custom Answer implementations.

Mockito is a powerful tool for creating mock objects in Java to mock generic and regular classes. By using the when() and thenReturn() methods, the @Captor annotation, and the Answer interface, you can set up the desired behavior of your mock objects. This will allow you to test your code in various situations.

However, I advise you to check out Waldo's extensive toolkit for UI testing if you want to make sure that your code is reliable and safe. Even for nondevelopers, it is incredibly accessible and doesn't require any code.

Start scripting in minutes!

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Kohei Nozaki's blog  Notes of my experiments -->

• JUnit and Mockito tips

Posted on Friday Jul 03, 2020 at 06:40PM in Technology

In this entry I’ll share some tips about JUnit and Mockito for making unit tests better.

Mockito annotations

Mockito has some annotations that can be used for reducing redundancy of tests:

@InjectMocks

Before looking into the usage of those annotations, let’s assume we have the following production code which consists of 2 classes.

The first one is called MailServer, which has a method called send() that sends an SMTP message which this object receives as the parameter of the method. Note that the MailServer class most probably needs to be mocked out when you want to write a unit test for a class which uses the MailServer class because it really opens a TCP connection to an SMTP server, which is not a preferable thing for unit tests.

The other class is called Messenger, which depends on the MailServer class. This class requires an instance of the MailServer class in its constructor. This class has a method called sendMail(), which has 3 parameters. The responsibility of this method is first constructing an SMTP message based on those 3 parameters and then asking the MailServer object to send the SMTP message. It also does quick error handling which translates IOException into an unchecked one with embedding the content.

Let’s try writing a unit test for the Messenger class. But we don’t want to use the real MailServer class because it really tries to open a connection to an SMTP server. It will make testing harder because in order to test with the real MailServer class, we really need an SMTP server which is up and running. Let’s avoid doing that and try using a mocked version of a MailServer instance for the testing here.

A happy path test case would look like the following:

In the setUp() method, a mock MailServer object is created and injected into the constructor of the Messenger class. And in the test() method, first we create the expected SMTP message which the Messenger class has to create, then we call the sendMail() method and finally we verify that the send() method of the mock MailServer object has been called with the expected SMTP message.

With annotations, the test above can be written as follows:

First we annotate the test class with @ExtendWith(MockitoExtension.class) (Note that it’s a JUnit5 specific annotation, so for JUnit4 tests we need something different). Having the test class annotated with that one, when there is a field annotated with @Mock in the test class, Mockito will automatically create a mock for the field and inject it. And when there is a field annotated with @InjectMocks, Mockito will automatically create a real instance of the declared type and inject the mocks that are created by the @Mock annotation.

This is especially beneficial when many mock objects are needed because it reduces the amount of repetitive mock() method calls and also removes the need for creating the object which gets tested and injecting the mocks into the object.

And also it provides a clean way to create a mock instance of a class which has a parameterized type. When we create a mock instance of the Consumer class, a straightforward way would be the following:

The problem here is that it produces an unchecked assignment warning. Your IDE will complain about it and you will get this warning when the code compiles with -Xlint:unchecked :

With the @Mock annotation, we can get rid of the warning:

There is another useful annotation called @Captor. Let’s see the following test case:

The @Captor annotation creates an object called ArgumentCaptor which captures a method parameter of a method call of a mock object. In order to capture a parameter with an ArgumentCaptor, first we need to call the capture() method in a method call chain of the Mockito.verify() method. Then we can get the captured value with the getValue() method and we can do any assertion against it. It’s especially useful in a situation where checking the equality is not sufficient and a complex verification is needed.

AssertJ is an assertion library for unit tests written in Java. It provides better readability and richer assertions than its older equivalents like the one shipped with JUnit. Let’s see some example code from the official website :

A unique feature of AssertJ is that all of the assertions here begin with the method assertThat() which receives the parameter that gets asserted. After that we specify the conditions the parameter needs to fulfill. An advantage of this approach is that we can specify multiple conditions with method call chain. It’s more readable and less verbose than the old way where repetitive assertTrue() or assertEquals() calls are involved. It also provides rich assertions for widely used classes like List, Set or Map.

Another useful feature of AssertJ is for verifying an unhappy path where an Exception is involved. Let’s remember the production code we used in the Mockito annotation section and consider a situation where the MailServer cannot connect to the SMTP server. Due to that, the send() method throws IOException. In this situation, the Messenger class is expected to catch the IOException and translate it into UncheckedIOException with the SMTP message embedded. A unit test for this can be written as follows with AssertJ:

First we make the mock MailServer instance throw IOException when its send() method is called. After that we pass a lambda expression which calls the sendMail() method to the assertThatThrownBy() method of AssertJ. After that we can do various assertions. What we are checking here is that the sendMail() method throws UncheckedIOException with the SMTP message embedded and it also contains a parent Exception whose class is IOException.

We’ve discussed some tips about Mockito and the basic uses of AssertJ for test cases that are written in JUnit. Both Mockito and AssertJ have extensive documents and rich functionality which greatly helps writing unit tests. I highly recommend checking the references below:

Mockito framework site

AssertJ - fluent assertions java library

Practical Unit Testing: JUnit 5, Mockito, TestNG, AssertJ - book by Tomek Kaczanowski

The pieces of code which are used in this entry can be found on GitHub: https://github.com/nuzayats/junittips

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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 .

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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 :

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Java Program to Handle Unchecked Exception

Exceptions are the issues arising at the runtime resulting in an abrupt flow of working of the program. Remember exceptions are never thrown at the compile-time rather always at runtime be it of any type. No exception is thrown at compile time. Throwable Is super-class of all exceptions and errors too. Now there is an urgency to deal with them for which a concept is defined in Java language known as ‘Exception Handling Techniques’

There are two types of exceptions defined as follows 

• Checked Exceptions
• Unchecked Exceptions

Real-world Illustration: Exceptions

Consider an employee leaving home for office. He is being monitored by the parent to take ID card stuff and all things as they can think of. Though the employee knows out everything but still being monitored. Now employee leaves out the home still somehow was delayed as his vehicle tyre gets punctured because of which result is that he arrived late to office. Now these wanted things that disrupt his daily routine is referred as Exceptions in Java. Parent actions that helped him though he checked those stuffs but if someday somehow missed and the employee gets things correctly at home itself is referred as ‘checked exception’ in Java. The actions over which parental access does not have any control is referred as ‘unchecked exceptions.’ Here, parent or monitoring authority is referred as ‘Compilers’ in programming languages. Exceptions that can be detected by compilers are checked exceptions and those who can not be detected are called unchecked exceptions.

Approach: Now, in order to deal with exceptions, the concept proposed out are exception handling techniques. Straight away diving onto the concept for unchecked exceptions.

Unchecked Exception

These types of Exceptions occur during the runtime of the program.  These are the exceptions that are not checked at a compiled time by the compiler. In Java exceptions under Error and Runtime Exception classes are unchecked exceptions, This Exception occurs due to bad programming.

• Errors class Exceptions like  StackOverflow, OutOfMemoryError exception, etc are difficult to handle
• Runtime Exceptions like IndexoutOfBoundException, Nullpointer Exception, etc can be handled with the help of try-Catch Block

There are 2 major Unchecked Exceptions which are faced generally by programmers namely IndexOutOfBoundsExcepetion and NullPointerException . They are discussed below with the help of an example also, we will implement them and discuss how to handle them out. Both the major approaches are proposed as below:

• IndexOutOfBoundsException
• NullPointerException

Case 1: (Array)IndexoutOfBoundException : This Exception occurs due to accessing the index greater than and equal to the size of the array length. The program will automatically be terminated after this exception. In simpler terms, a memory is being tried to accessed which the current data structure is not holding by itself. Here this exception is defined over data structure namely ‘ Arrays ‘.

Handling ArrayIndexoutOfBoundException : Try-catch Block we can handle this exception try statement allows you to define a block of code to be tested for errors and catch block captures the given exception object and perform required operations . The program will not terminate.

Case 2: NullPointerException: This exception occurs when trying to access the object reference that has a null value.

Handling Technique for NullPointerException

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Checked and Unchecked Exceptions in Java

Last updated: January 8, 2024

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1. Overview

Java exceptions fall into two main categories: checked exceptions and unchecked exceptions.

In this tutorial, we’ll provide some code samples on how to use them.

2. Checked Exceptions

In general, checked exceptions represent errors outside the control of the program. For example, the constructor of FileInputStream  throws FileNotFoundException if the input file does not exist.

Java verifies checked exceptions at compile-time.

Therefore, we should use the throws keyword to declare a checked exception:

We can also use a try-catch block to handle a checked exception:

Some common checked exceptions in Java are IOException , SQLException  and ParseException .

The Exception class is the superclass of checked exceptions, so we can create a custom checked exception by extending Exception :

3. Unchecked Exceptions

If a program throws an unchecked exception, it reflects some error inside the program logic.

For example, if we divide a number by 0, Java will throw ArithmeticException :

Java does not verify unchecked exceptions at compile-time. Furthermore, we don’t have to declare unchecked exceptions in a method with the throws  keyword. And although the above code does not have any errors during compile-time, it will throw ArithmeticException at runtime.

Some common unchecked exceptions in Java are NullPointerException , ArrayIndexOutOfBoundsException  and IllegalArgumentException .

The RuntimeException class is the superclass of all unchecked exceptions, so we can create a custom unchecked exception by extending RuntimeException :

4. When to Use Checked Exceptions and Unchecked Exceptions

It’s a good practice to use exceptions in Java so that we can separate error-handling code from regular code. However, we need to decide which type of exception to throw. The Oracle Java Documentation provides guidance on when to use checked exceptions and unchecked exceptions:

“If a client can reasonably be expected to recover from an exception, make it a checked exception. If a client cannot do anything to recover from the exception, make it an unchecked exception.”

For example, before we open a file, we can first validate the input file name. If the user input file name is invalid, we can throw a custom checked exception:

In this way, we can recover the system by accepting another user input file name.

However, if the input file name is a null pointer or it is an empty string, it means that we have some errors in the code. In this case, we should throw an unchecked exception:

5. Conclusion

In this article, we discussed the difference between checked and unchecked exceptions. We also provided some code examples to show when to use checked or unchecked exceptions.

As always, all code in this article can be found over on GitHub .

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