定义

实例方法：可以对当前对象的实例变量进行操作，也可以对类变量进行操作，由实例对象调用。
类方法：不能访问实例变量，只能访问类变量。由类名或者实例对象调用，不能出现this或者super关键字。

Demo

package com.lanjerry;

public class Demo0717 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        People p1=new People("小明",18,100);
        p1.show();
        People p2=new People("小明",18,200);
        p1.show();
        p2.show();
        p1.change(300);
        p1.show();
        p2.change(400);
        p1.show();
        p2.show();
    }

}

class People{
    String name;
    int age;
    static int weight;
    
    People(String name,int age,int weight)
    {
        this.name=name;
        this.age=age;
        this.weight=weight;
    }
    
    public void show()
    {
        System.out.println("name is:"+this.name+"  age is:"+this.age+" weight is:"+this.weight);
    }
    public static void change(int weight)
    {
        //this.weight=weight;//报错，内容：Cannot use this in a static context
        People.weight=weight;
    }
}

Result

name is:小明 age is:18 weight is:100
name is:小明 age is:18 weight is:200
name is:小明 age is:18 weight is:200
name is:小明 age is:18 weight is:300
name is:小明 age is:18 weight is:400
name is:小明 age is:18 weight is:400