Interface annotation in Java

Interface annotation in Java

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Interface Annotation in Java:

In Java, an interface is a abstract class that contains only constant declarations and abstract method declarations. It defines a contract that must be implemented by any class that implements it. An interface can have multiple implementations or inheritance relationships with other interfaces.

A typical interface declaration starts with the interface keyword followed by the name of the interface. Inside the interface, you can declare:

Here's an example of an interface declaration in Java:

public interface Printable {
void print();
}

To use this interface, you would create a class that implements it. For example:

public class MyPrintable implements Printable {
public void print() {
System.out.println("Printing something...");
}
}

In the MyPrintable class, we are implementing the print() method declared in the Printable interface.

When you create an instance of the MyPrintable class and call its print() method, it will print "Printing something..." to the console.

Here's another example where a class implements multiple interfaces:

public class MyDocument implements Printable, Editable {
public void print() {
System.out.println("Printing a document...");
}
public void edit() {
System.out.println("Editing a document...");
}
}

In this case, the MyDocument class implements both the Printable and Editable interfaces. It provides its own implementation for the print() method declared in the Printable interface and the edit() method declared in the Editable interface.

Interface annotation is a powerful feature in Java that allows you to define contracts and abstract methods. By using interfaces, you can decouple the contract (what) from the implementation (how), which makes your code more modular, flexible, and reusable.

In real-world scenarios, interfaces are used extensively for:

I hope this helps! Let me know if you have any further questions or clarifications.

Target annotation in java example

Here is a Java example of target annotation:

import java.lang.annotation.*;
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Loggable {
String message() default "Method executed";
}

In this code, we are creating an annotation called Loggable which can be applied to a method.

The @Target annotation specifies the type of Java element that this annotation can be used on. In this case, it is METHOD, so only methods can have this annotation.

The @Retention annotation specifies how long this annotation should be retained. We are specifying that this annotation should be kept until runtime (RUNTIME).

Inside the Loggable interface, we are declaring a single method called message. This method returns a string and has a default value of "Method executed". This means that when an annotation is not specified for a method, it will automatically have this message as its value.

Here is how you can use this annotation in your code:

public class Example {
@Loggable("This is my own log message")
public void myMethod() {
System.out.println("Hello");
}
}

In the above example, we are applying the @Loggable annotation to our myMethod. If you print out the message of this annotated method using a reflection-based logging framework (for instance), it would say "This is my own log message".