What is the use of this in java-JavaBase-php.cn

What is the use of this in java

藏色散人

Release： 2019-11-13 11:29:12

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java What is this used for?

The role of this keyword in java

1. this calls the current attribute: Its main function is when the data in the class needs to be initialized. You can assign values through this instead of just defining a variable for assignment, which is more conducive to code reading and understanding.

For example:

class Book{//定义书的类
    private String name;//书本名字
    private int price;//书本价格
    public Book(String name,int price){ //使用this对类的数据进行初始化
        this.name = name;        
　　　 　this.price = price;
    }
    /*public Book(String n,int p){ //若不使用this关键字只能这样进行赋值，不利于将变量与属性统一起来
        name = n;
        price = p;
    }*/
    public String getInfo(){
        return "书籍：" + name + ",价格：" + price;
    }
}
public class ThisDemo{
    public static void main(String args[]){
        System.out.printIn(new Book("Java",89.9).getInfo())
    }
}

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2. this call Methods (ordinary methods, constructor methods)

　 (1) Ordinary methods:

class Book{//定义书的类
    private String name;//书本名字
    private int price;//书本价格
    public Book(String name,int price){//使用this对类的数据进行初始化
        this.name = name; 6         this.price = price;
        this.print();//调用本类普通方法，虽然可以不用使用this也可以进行本类普通方法的调用，但是好的习惯最好应该加上，目的是可以区分方法的定义来源
    }
    public String getInfo(){
        return "书籍：" + name + ",价格：" + price;
    }
    public void print(){
        System.out.printIn("***********");
    }
}
public class ThisDemo{
    public static void main(String args[]){
        System.out.printIn(new Book("Java",89.9).getInfo())
    }
}

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　 (2) Constructor methods: The difference between ordinary methods and constructor methods is that constructor methods can only be used after they are created. Once, used to initialize data, while ordinary methods can be called multiple times after creation.

When you need to use the constructor method to output the same repeated content, if you do not use this keyword, you can only use the following code:

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class Book{//定义书的类
    private String name;//书本名字
    private int price;//书本价格
    public Book(){//无参构造
        System.out.printIn("*************");
    }
    public Book(String name){//一参构造
        System.out.printIn("*************");
        this.name = name;
    }
    public Book(String name,int price){//二参构造
        System.out.printIn("*************");
        this.name = name;
        this.price = price;
        }
    public String getInfo(){
        return "书籍：" + name + ",价格：" + price;
    }
}
public class ThisDemo{
    public static void main(String args[]){
        System.out.printIn(new Book("Java",89.9).getInfo())
    }
}

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Obviously, this greatly Lines of code are wasted. Instead, this should be used to call the constructor. The method is as follows:

class Book{//定义书的类
    private String name;//书本名字
    private int price;//书本价格
    public Book(){//无参构造
        System.out.printIn("*************");
    }
    public Book(String name){//一参构造
        this();//调用本类中的无参构造
        this.name = name;
    }
    public Book(String name,int price){//二参构造
        this(name);//调用本类中的一参构造
        this.price = price;
        }
    public String getInfo(){
        return "书籍：" + name + ",价格：" + price;
    }  

}
public class ThisDemo{
    public static void main(String args[]){
        System.out.printIn(new Book("Java",89.9).getInfo())
    }
}

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Note: The call to this must be the first statement in the constructor, otherwise an error will occur. Of course, it cannot Call the constructor in a normal method.

The most important thing is that using this call cannot form a loop, that is, it cannot form a recursive call without an exit.

3. this represents the current method

class Book{
    
    public void fun(){
        System.out.printIn("FUN方法"+this);
    }
    }
}
public class ThisDemo{
    public static void main(String args[]){
        Book b1 = new Book();
        System.out.printIn("MAIN方法"+b1);
        b1.fun();//有b1调用fun方法（this = b1）
        //两个输出结果的地址一样，代表着此时this代表着b1
        System.out.printIn("*************")
        Book b2 = new Book();
        System.out.printIn("MAIN方法"+b2);
        b2.fun();//此时输出结果和b2一样
    }
}

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During the entire process, the definition of this has not changed. As long as a certain object calls a method in this class, at this time this represents the currently executing object.

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