This of Java keyword

concept

This keyword can only be used inside a method to refer to the "object calling the method". Specifically. There are two situations:

package com.my.pac09;

/*
 *  ThisTest.java
 *  this  对“调用方法那个对象”的引用
 */

public class ThisTest {
    private int height;
    public int width;

    public void setHeight(int height) {
        //this.height代表对象属性，和形参height进行区分
        this.height = height;
    }

    public int getHeight() {
        //省略了this,下面两句效果相同
        //都显示正在调用method方法。
        method();
        this.method();
        return this.height;
    }

    public ThisTest addOneToWidth() {
        //this代表正在调用addOneToWidth方法的对象的引用
        this.width++;
        System.out.println("宽度加一，现在是："+this.width);
       //返回该对象的引用
        return this;
    }

    public ThisTest(int height) {
        this.height = height;
    }

    public ThisTest(int height,int width) {
        //调用ThisTest(int height)构造器
        this(height);
        this.width = width;
    }

    public void method() {
        System.out.println("正在调用method方法");
    }
}

/*ThisAllTest.java*/
package com.my.pac09;

public class ThisAllTest {
    public static void main(String[] args) {
        ThisTest test = new ThisTest(1,2);
        System.out.println("高度为：" + test.getHeight() + "，宽度为： " + test.width);
        ThisTest me = test.addOneToWidth().addOneToWidth();
    }
}

//测试结果
正在调用method方法
正在调用method方法
高度为：1，宽度为： 2
宽度加一，现在是：3
宽度加一，现在是：4

Form of expression

 public int getHeight() {
    //省略了this,下面两句效果相同
    //都显示正在调用method方法。
    method();
    this.method();
    return this.height;
}

//结果
正在调用method方法
正在调用method方法

public ThisTest addOneToWidth() {
    //this代表正在调用addOneToWidth方法的对象的引用
    System.out.println("宽度加一，现在是："+this.width);
    this.width++;
    //返回该对象的引用
    return this;
}
    
ThisTest me = test.addOneToWidth().addOneToWidth();

//结果
宽度加一，现在是：3
宽度加一，现在是：4

public ThisTest(int height) {
    this.height = height;
}

public ThisTest(int height,int width) {
    //调用ThisTest(int height)构造器
    this(height);
    this.width = width;
}

public void setHeight(int height) {
    //this.height代表对象属性，和形参height进行区分
    this.height = height;
}

package com.my.pac09;
/*PassingThis.java*/
public class PassingThis {
    public static void main(String[] args) {
        Person p = new Person();
        Apple apple = new Apple(5);
        apple.displayPeelNum();//此时皮的数量：5
        p.eat(apple);
    }
}
class Person {
    public void eat(Apple apple) {
        System.out.println("开始剥皮...");
        Apple peeled = apple.getPeeled();
        peeled.displayPeelNum();
        System.out.println("剥完的苹果就是好吃~");
    }
}
class Apple {
    public int num;
    //构造器，传入皮的数量
    Apple(int num){
        this.num = num;
    }
    Apple getPeeled() {
        //意思是把apple传给Peeler的peel方法剥皮，this代表传进去的apple
        return Peeler.peel(this);
    }
    void displayPeelNum() {
        System.out.println("此时皮的数量：" + num);
    }
}
class Peeler {
    //static修饰的类方法，可以直接利用Peeler.peel(..)调用
    static Apple peel(Apple apple) {
        //...remove peel 剥皮的过程
        while (apple.num > 0) apple.num--;
        return apple;
    }
}

//测试结果
此时皮的数量：5
开始剥皮...
此时皮的数量：0
剥完的苹果就是好吃~

PS: if there are mistakes in the article, you are welcome to criticize and correct! Reference books: Thinking in Java, crazy Java handout