Java 9 Interface Private Methods

by Online Tutorials Library July 14, 2022

Java 9 Private Interface Methods

In Java 9, we can create private methods inside an interface. Interface allows us to declare private methods that help to share common code between non-abstract methods.

Before Java 9, creating private methods inside an interface cause a compile time error. The following example is compiled using Java 8 compiler and throws a compile time error.

Java 9 Private Interface Methods Example

  interface Sayable{  default void say() {  saySomething();  }  // Private method inside interface  private void saySomething() {  System.out.println(“Hello… I’m private method”);  }  }  public class PrivateInterface implements Sayable {  public static void main(String[] args) {  Sayable s = new PrivateInterface();  s.say();  }  }  

Output:

PrivateInterface.java:6: error: modifier private not allowed here

Note: To implement private interface methods, compile source code using Java 9 or higher versions only.

Now, lets execute the following code by using Java 9. See the output, it executes fine.

Java 9 Private Interface Methods Example

  interface Sayable{  default void say() {  saySomething();  }  // Private method inside interface  private void saySomething() {  System.out.println(“Hello… I’m private method”);  }  }  public class PrivateInterface implements Sayable {  public static void main(String[] args) {  Sayable s = new PrivateInterface();  s.say();  }  }  

Output:

Hello... I'm private method

Such like, we can also create private static methods inside an interface. See, the following example.

Java 9 Private Static Methods Example

  interface Sayable{  default void say() {  saySomething(); // Calling private method  sayPolitely(); //  Calling private static method  }  // Private method inside interface  private void saySomething() {  System.out.println(“Hello… I’m private method”);  }  // Private static method inside interface  private static void sayPolitely() {  System.out.println(“I’m private static method”);  }  }  public class PrivateInterface implements Sayable {  public static void main(String[] args) {  Sayable s = new PrivateInterface();  s.say();  }  }  

Output:

Hello... I'm private method  I'm private static method

Next TopicTry-With Resources

Java 9 Interface Private Methods

Java 9 Private Interface Methods

Java 9 Private Interface Methods Example

Note: To implement private interface methods, compile source code using Java 9 or higher versions only.

Java 9 Private Interface Methods Example

Java 9 Private Static Methods Example

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