JVM分派

1.静态分派-针对方法重载

package com.example.demo.dispatch;

public class StaticDispatch {
    public static void main(String[] args) {
        Human man = new Man() ;
        Human woman = new Woman();

        sayHello(man);
        sayHello(woman);
    }

    static abstract class Human {
    }

    static class Man extends Human {
    }

    static class Woman extends Human {
    }

    public static void sayHello(Human human) {
        System.out.println("Hi I am human");
    }

    public static void sayHello(Man human) {
        System.out.println("Hi I am Man");
    }

    public static void sayHello(Woman human) {
        System.out.println("Hi I am Woman");
    }
}

输出结果是

Hi I am human
Hi I am human

Human是静态类型或外观类型，后面指向的Man则是实际类型。静态类型的变化仅在使用时发生，实际类型实在运行时才能确定。在重载时是根据静态类型而不是实际类型判断的

        sayHello((Man) man);
        sayHello((Woman) woman);

有些情况编译器无法推断出唯一的版本时，往往只能确定一个“更加适合的版本”

package com.example.demo.dispatch;

import java.io.Serializable;

public class Overload {


    public static void main(String[] args) {

        sayHello('a');

    }

    public static void sayHello(Object object) {
        System.out.println("Hi I am object");
    }


    public static void sayHello(int object) {
        System.out.println("Hi I am int");
    }

    public static void sayHello(long object) {
        System.out.println("Hi I am long");
    }

    public static void sayHello(char object) {
        System.out.println("Hi I am char");
    }
  public static void sayHello(char... object) {
        System.out.println("Hi I am char");
    }

    public static void sayHello(Serializable object) {
        System.out.println("Hi I am char");
    }

}

char>int>long>float>double>serializable>可变参数

2.动态分派-针对方法重写

package com.example.demo.dispatch;

public class DynamicDispatch {
    public static void main(String[] args) {
        Human man = new Man() ;
        Human woman = new Woman();

        man.sayHello();
        woman.sayHello();
        
        man = new Woman();
        man.sayHello();
        
    }

    static abstract class Human {
        abstract void sayHello();
    }

    static class Man extends Human {
        public void sayHello() {
            System.out.println("Hi I am human");
        }
    }

    static class Woman extends Human {
        public void sayHello() {
            System.out.println("Hi I am Woman");
        }
    }
}

Hi I am human
Hi I am Woman
Hi I am Woman

3.单分派和多分派
单分派：一个宗量对目标方法进行选择
多分派：多个宗量对目标方法进行选择

package com.example.demo.dispatch;

public class Dispatch {
    public static void main(String[] args) {
        Father father = new Father();
        Father son = new Son();

        father.choice(new _360());
        son.choice(new QQ());
    }

    static class _360{}

    static class QQ{}


    static class Father  {
        public void choice(_360 args) {
            System.out.println("father I am 360");
        }
        public void choice(QQ qq) {
            System.out.println("father I am QQ");
        }
    }

    static class Son extends Father  {
        public void choice(_360 args) {
            System.out.println("son I am 360");
        }
        public void choice(QQ qq) {
            System.out.println("son I am QQ");
        }
    }
}

father I am 360
son I am QQ

4.虚拟机动态分派实现

---来源深入理解java虚拟机