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publicinterface SimpleInterface {

  publicvoid doSomeWork();

}

classSimpleInterfaceImpl implementsSimpleInterface{

  @Override

  publicvoid doSomeWork() {

    System.out.println("Do Some Work implementation in the class");

  }

  publicstatic void main(String[] args) {

    SimpleInterfaceImpl simpObj = newSimpleInterfaceImpl();

    simpObj.doSomeWork();

  }

}

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publicinterface SimpleInterface {

  publicvoid doSomeWork();

  publicvoid doSomeOtherWork();

}

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$javac .\SimpleInterface.java

.\SimpleInterface.java:18: error: SimpleInterfaceImpl is not abstract and does not

override abstract method doSomeOtherWork() inSimpleInterface

class SimpleInterfaceImpl implements SimpleInterface{

^

1 error

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publicinterface SimpleInterface {

  publicvoid doSomeWork();

  //A default method in the interface created using "default" keyword

  //使用default关键字创在interface中直接创建一个default方法，该方法包含了具体的实现代码

  defaultpublic void doSomeOtherWork(){

    System.out.println("DoSomeOtherWork implementation in the interface");

  }

}

classSimpleInterfaceImpl implementsSimpleInterface{

  @Override

  publicvoid doSomeWork() {

    System.out.println("Do Some Work implementation in the class");

  }

  /*

   * Not required to override to provide an implementation

   * for doSomeOtherWork.

   * 在SimpleInterfaceImpl里，不需要再去实现接口中定义的doSomeOtherWork方法

   */

  publicstatic void main(String[] args) {

    SimpleInterfaceImpl simpObj = newSimpleInterfaceImpl();

    simpObj.doSomeWork();

    simpObj.doSomeOtherWork();

  }

}

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Do Some Work implementation inthe class

DoSomeOtherWork implementation inthe interface

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publicinterface InterfaceWithDefaultMethod {

  publicvoid someMethod();

  defaultpublic void someOtherMethod(){

    System.out.println("Default method implementation in the interface");

  }

}

publicinterface InterfaceWithAnotherDefMethod {

  defaultpublic void someOtherMethod(){

    System.out.println("Default method implementation in the interface");

  }

}

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publicclass DefaultMethodSample implements

  InterfaceWithDefaultMethod, InterfaceWithAnotherDefMethod{

  @Override

  publicvoid someMethod(){

    System.out.println("Some method implementation in the class");

  }

  publicstatic void main(String[] args) {

    DefaultMethodSample def1 = newDefaultMethodSample();

    def1.someMethod();

    def1.someOtherMethod();

  } 

}