static

 

package oop.redo;

public class Demo1 {
    private static int a;
    private double b;
    public static void main(String[] args) {
        Demo1.a=1;
        System.out.println(Demo1.a);
        Demo1  a= new Demo1();
        a.b=0.4;
        System.out.println(a.b);
        a.go();// No, static The modifier needs to be called first new An object 
        run();// Yes static Can be called directly 
    }
    public void go() {
        System.out.println("go");
    }
    public static void run() {
        System.out.println("run");
    }
}

abstract class

 

package oop.redo;
// abstract class 
public abstract  class Demo2 {
    public abstract void Sun();
}

package oop.redo;
//demo3 Inherit demo2 The abstract class of , But it needs to be rewritten demo2 Abstract methods in 
public class Demo3 extends Demo2{
    @Override
    public void Sun() {
        System.out.println("say hi");
    }
}

Interface

 

 

 

package oop.redo;

public interface Userservice {
    void add(String name);
    void delete(String name);
    void update(String name);
    void select(String name);
}

package oop.redo;
// Class overrides methods in the interface 
public class Userserviceimp implements Userservice{
    @Override
    public void add(String name) {
        System.out.println(name);
    }

    @Override
    public void delete(String name) {
        System.out.println(name);
    }

    @Override
    public void update(String name) {
        System.out.println(name);
    }

    @Override
    public void select(String name) {
        System.out.println(name);
    }

}