In this tutorial, I’ll explain about Interfaces in Java.
What is Interface?
An interface is a group of related methods with empty bodies (abstract methods).
- All the methods in Interface are public and abstract.
- A class can implement more than one interface.
- An interface can extends another interface or interfaces
- A class that implements interface must implements all the methods in interface. To implement interface use implements keyword.
- The variables declared in an interface are public, static & final by default.
- Java does not support multiple inheritance in case of class, but by using interface it can achieve multiple inheritance .
Syntax of Interface
interface test {
//declare methods which are abstract by default
//declare variables which are public, static, final by default
}
Relationship between Class and Interfaces
Below is an example of implementation of Interface. I have declared a class as Interface which have two abstract methods.
public interface MyInterface {
// Abstract methods
public void method1();
public void method2();
}
Interface Implementation
public class InterfaceTest implements MyInterface {
public void method1() {
System.out.println("Implementation of Method 1");
}
public void method2() {
System.out.println("Implementation of Method 2");
}
public static void main(String[] args) {
MyInterface interTest = new InterfaceTest();
interTest.method1();
interTest.method2();
}
}
Output
Implementation of Method 1
Implementation of Method 2
Multiple Interface
In the below example, Interface 2 extends Interface 1 and class implements Interface 2.
Interface 1
public interface Infa1 {
public void method1();
}
Interface 2
public interface Infa2 extends Infa1 {
public void method2();
}
MultipleInterfaceTest Class
public class MultipleInterfaceTest implements Infa2 {
public void method1() {
System.out.println("Implementation of Method 1");
}
public void method2() {
System.out.println("Implementation of Method 2");
}
public static void main(String[] args) {
Infa2 obj = new MultipleInterfaceTest();
obj.method1();
obj.method2();
}
}
Output
Implementation of Method 1
Implementation of Method 2
Multiple Inheritance
Interface supports multiple Inheritance. Here, there are two interfaces which are implemented in class MultipleInheritanceTest.
Interface 1
public interface Infa1 {
public void method();
}
Interface 2
public interface Infa2 {
public void method();
}
MultipleInheritanceTest Class
public class MultipleInheritanceTest implements Infa1, Infa2 {
public void method() {
System.out.println("Implementation of Method ");
}
public static void main(String[] args) {
MultipleInheritanceTest test = new MultipleInheritanceTest();
test.method();
}
}
Output
Implementation of Method
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