JDK8新特性，给接口添加一个默认实现

package interfacetest;

public interface TestInterface {
    
    default int add(int x, int y) {
        return x+y;
    }
    
    int sub(int x, int y);
    
}

package interfacetest;

public class TestInterfaceClass implements TestInterface {

    @Override
    public int sub(int x, int y) {
        return x-y;
    }
    
    
    public static void main(String[] args) {
        TestInterfaceClass testClass = new TestInterfaceClass();
        System.out.println(testClass.add(1, 2));
        System.out.println(testClass.sub(1, 2));
    }
    
}