How does override work in Java internally?

How does override work in Java internally?

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Override is a fundamental concept in object-oriented programming (OOP) in Java, allowing subclasses to provide customized implementations of methods that are inherited from their parent classes. But have you ever wondered how this magic happens behind the scenes? Let's dive into the internal workings of method overriding in Java.

Method Overriding Basics

To start with, let's briefly review what method overriding is all about. When a subclass (the "overrider") provides its own implementation for a method that is already defined in its parent class (the "overridee"), this is called method overriding. The overriding method must have the same name, return type, and parameter list as the original method in the superclass.

Java Virtual Machine (JVM) Perspective

From the JVM's perspective, method overriding works as follows:

a. Is the method being invoked defined in the subclass? If so, execute the subclass's implementation.

b. If not, look up the method's definition in the superclass and its parent classes recursively until reaching the object's class (i.e., the root of the inheritance hierarchy).

Bytecode Manipulation

When a subclass overrides a method, the JVM must modify the bytecode for the overridden method to ensure that the correct implementation is called at runtime. This involves two main steps:

Conclusion

In summary, when you override a method in Java, the JVM performs several crucial steps behind the scenes:

By understanding these internal workings, you'll gain insight into how Java's dynamic dispatch mechanism makes overriding methods possible, allowing for more flexible and modular programming.

Now, go forth and conquer those OOP challenges with confidence!

Java unit test custom annotation

Here is a comprehensive overview of creating custom annotations for unit tests in Java.

What are Annotations?

Annotations are special kinds of comments that you can apply to your code. They're used to provide additional information about the code, and they don't affect the program's behavior directly. In other words, annotations are metadata about your code.

Why Use Custom Annotations for Unit Tests?

You might want to use custom annotations for unit tests if you have a specific requirement that needs to be met before a test is considered successful or if you need more control over how the tests are executed. Here are some reasons why:

How to Create a Custom Annotation?

Creating a custom annotation in Java is quite straightforward:

Here's a simple example of creating a custom annotation called @TestPriority:

// Define the annotation interface
public @interface TestPriority {
int value();
}
// Usage:
@TestPriority(1)
public void testSomething() { ... }

How to Use Your Custom Annotation with JUnit

To use your custom annotation in a JUnit test, you'll need to create a custom TestRunner class. Here's an example:

import org.junit.runners.BlockJUnit4ClassRunner;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
@Retention(RetentionPolicy.RUNTIME)
public @interface JUnitCustomAnnotation {
Class<?>[] classes();
}
@RunWith(JUnitCustomAnnotation.class)
public class CustomTestRunner extends BlockJUnit4ClassRunner {
public CustomTestRunner(Class<?> klass) {
super(klass);
}
// Override the test method execution
protected Statement classify(final Statement statement, final FrameworkMethod methodInfo) {
// Add custom logic here based on your annotation
return statement;
}
}

You would then use this runner class for your tests:

@RunWith(CustomTestRunner.class)
@TestPriority(1)
public class MyTest {
// Test methods...
}

In this example, the CustomTestRunner class will be used to run all the test methods annotated with @TestPriority.

Conclusion

Creating custom annotations for unit tests in Java can help you customize your testing process and provide more control over how your tests are executed. You can use them to mark special types of tests, add metadata, or influence the behavior of your testing framework.

Remember to follow best practices when designing and using custom annotations:

Now, go forth and make the most of custom annotations for your unit tests!