总结一下jdk7~jdk9 Java 中接口概念的变化

1.在jdk 7 或更早版本中，接口里面只能有常量变量和抽象方法。这些接口方法必须由选择实现接口的类实现。

package com.tntxia;

public interface TempI {
    public abstract void method(int n);
}

package com.tntxia;

public class Temp implements TempI{
    @Override
    public void method(int n)
    {
        if (n % 2 == 0)
            System.out.println("geeksforgeeks");
        else
            System.out.println("GEEKSFORGEEKS");
    }

    public static void main(String[] args)
    {
        TempI in1 = new Temp();
        TempI in2 = new Temp();
        in1.method(4);
        in2.method(3);
    }
}

2.jdk8 的时候接口可以有默认方法和静态方法功能

public interface TempI {

    public abstract void div(int a, int b);

    public default void add(int a, int b)
    {
        System.out.print("Answer by Default method = ");
        System.out.println(a + b);
    }

    public static void mul(int a, int b)
    {
        System.out.print("Answer by Static method = ");
        System.out.println(a * b);
    }
}

package com.tntxia;

public class Temp implements TempI{



    @Override
    public void div(int a, int b)
    {
        System.out.print("Answer by Abstract method = ");
        System.out.println(a / b);
    }

    public static void main(String[] args)
    {
        TempI in = new Temp();
        in.div(8, 2);
        in.add(3, 1);
        TempI.mul(4, 1);
    }
}

3.Jdk 9 在接口中引入了私有方法和私有静态方法。

package com.tntxia;

public interface TempI {

    public abstract void mul(int a, int b);

    public default void
    add(int a, int b)
    {
// private method inside default method
        sub(a, b);

        // static method inside other non-static method
        div(a, b);
        System.out.print("Answer by Default method = ");
        System.out.println(a + b);
    }

    public static void mod(int a, int b)
    {
        div(a, b); // static method inside other static method
        System.out.print("Answer by Static method = ");
        System.out.println(a % b);
    }

    private void sub(int a, int b)
    {
        System.out.print("Answer by Private method = ");
        System.out.println(a - b);
    }

    private static void div(int a, int b)
    {
        System.out.print("Answer by Private static method = ");
        System.out.println(a / b);
    }
}

package com.tntxia;

public class Temp implements TempI{

    @Override
    public void mul(int a, int b)
    {
        System.out.print("Answer by Abstract method = ");
        System.out.println(a * b);
    }

    public static void main(String[] args)
    {
        TempI in = new Temp();
        in.mul(2, 3);
        in.add(6, 2);
        TempI.mod(5, 3);
    }
}