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What are the modifiers allowed for methods in an Interface in java?
An interface in Java is a specification of method prototypes. Whenever you need to guide the programmer or, make a contract specifying how the methods and fields of a type should be you can define an interface.
In Java 7
As of Java7 you can have only public, abstract as modifiers for the methods of an interface.
interface MyInterface{
public abstract void display();
public abstract void setName(String name);
public abstract void setAge(int age);
}Using any other modifier with the methods of an interface would lead to a compile time error.
From Java8
From Java8 onwards interfaces allow default methods and static methods.
- Static methods − A static method is declared using the static keyword and it will be loaded into the memory along with the class. You can access static methods using class name without instantiation.
- You need to call static method of an interface using the name of the interface.
Example
interface MyInterface{
public void demo();
public static void display() {
System.out.println("This is a static method");
}
}
public class InterfaceExample{
public void demo() {
System.out.println("This is the implementation of the demo method");
}
public static void main(String args[]) {
InterfaceExample obj = new InterfaceExample();
obj.demo();
MyInterface.display();
}
}Output
This is the implementation of the demo method This is a static method
- Default methods − A default method is a default implementation of a method of an interface, if you have default method in an interface, there is no need to implement it in the classes that already implement this interface.
- A default method is also known as defender method or virtual extension method. You can define a default method using the default keyword as −
default void display() {
System.out.println("This is a default method");
}Example
interface sampleInterface{
public void demo();
default void display() {
System.out.println("This is a default method");
}
}
public class DefaultMethodExample implements sampleInterface{
public void demo() {
System.out.println("This is the implementation of the demo method");
}
public static void main(String args[]) {
DefaultMethodExample obj = new DefaultMethodExample();
obj.demo();
obj.display();
}
}Output
This is the implementation of the demo method This is a default method
From java 9
From Java9 onwards interfaces allow private and private static methods.
Example
interface MyInterface {
public abstract void demo();
public default void defaultMethod() {
privateMethod();
staticPrivateMethod();
System.out.println("This is a default method of the interface");
}
public static void staticMethod() {
staticPrivateMethod();
System.out.println("This is a static method of the interface");
}
private void privateMethod(){
System.out.println("This is a private method of the interface");
}
private static void staticPrivateMethod(){
System.out.println("This is a static private method of the interface");
}
}
public class InterfaceMethodsExample implements MyInterface {
public void demo() {
System.out.println("Implementation of the demo method");
}
public static void main(String[] args){
InterfaceMethodsExample obj = new InterfaceMethodsExample();
obj.defaultMethod();
obj.demo();
MyInterface.staticMethod();
}
}Output
This is a private method of the interface This is a static private method of the interface This is a default method of the interface Implementation of the demo method This is a static private method of the interface This is a static method of the interface
Updated on: 30-Jul-2019
3K+ Views
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