What are the rules for private methods in interfaces in Java 9?

Java 9 adds privatemethodsnew features in interface. Private methods can be defined using the private modifier. We can add private and privatestaticmethods in the interface of

Java 9

Rules for private methods in interfaces:

• Having the body of a private method in the interface means that we cannot declare it as a normal abstract method as we usually do in interfaces. If we try to declare a private method without a body, then it may throw an error saying "This method requires a body and not a semicolon ".
• We cannot use private and abstract modifiers simultaneously in an interface.
• If we want to access a private method from a static method in the interface, then the method can be declared as Private static method because we cannot make a static reference to a non-static method .
• A A private static method used in a non-static context means that it can be called from the default method in the interface.

Syntax

<strong>interface <interface-name> {
   private methodName(parameters) {
      // some statements
   }
}</strong>

Example

interface TestInterface {
   <strong>default </strong>void methodOne() {
      System.out.println("This is a Default method One...");
      printValues(); // calling a private method
   }
   <strong>default </strong>void methodTwo() {
      System.out.println("This is a Default method Two...");
      printValues(); // calling private method...
   }
   <strong>private </strong>void <strong>printValues</strong><strong>()</strong> { <strong>// private method in an interface
</strong>      System.out.println("methodOne() called");
      System.out.println("methodTwo() called");
   }
}
public class PrivateMethodInterfaceTest implements TestInterface {
   public static void main(String[] args) {
      TestInterface instance = new PrivateMethodInterfaceTest();
      instance.methodOne();
      instance.methodTwo();
   }
}

Output

<strong>This is a Default method One...
methodOne() called
methodTwo() called
This is a Default method Two...
methodOne() called
methodTwo() called</strong>

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