What is the use of this in java

1. This calls the current attribute: its main The function is that when you need to initialize the data in the class, you can assign the value through this instead of defining a variable for assignment, which is more conducive to the reading and understanding of the code (recommended tutorial: java tutorial)

class Book{//定義書的類
    private String name;//書本名字
    private int price;//書本價格
    public Book(String name,int price){ //使用this對類的數據進行初始化
        this.name = name;        
　　　 　   this.price = price;
    }
    /*public Book(String n,int p){ //若不使用this關鍵字只能這樣進行賦值，不利于將變量與屬性統(tǒng)一起來
        name = n;
        price = p;
    }*/
    public String getInfo(){
        return "書籍：" + name + ",價格：" + price;
    }
}
public class ThisDemo{
    public static void main(String args[]){
        System.out.printIn(new Book("Java",89.9).getInfo())
    }
}

2. this calling method (ordinary method, constructor method)

(1) Ordinary method:

class Book{//定義書的類
    private String name;//書本名字
    private int price;//書本價格
    public Book(String name,int price){//使用this對類的數據進行初始化
        this.name = name; 6         this.price = price;
        this.print();//調用本類普通方法，雖然可以不用使用this也可以進行本類普通方法的調用，但是好的習慣最好應該加上，目的是可以區(qū)分方法的定義來源
    }
    public String getInfo(){
        return "書籍：" + name + ",價格：" + 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())
    }
}

(2) Constructor method: The difference between ordinary methods and constructor methods is that the constructor method can only be used once after creation to initialize data, while the ordinary method is It 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 the this keyword, you can only use the following code:

class Book{//定義書的類
    private String name;//書本名字
    private int price;//書本價格
    public Book(){//無參構造
        System.out.printIn("*************");
    }
    public Book(String name){//一參構造
        System.out.printIn("*************");
        this.name = name;
    }
    public Book(String name,int price){//二參構造
        System.out.printIn("*************");
        this.name = name;
        this.price = price;
        }
    public String getInfo(){
        return "書籍：" + name + ",價格：" + price;
    }
}
public class ThisDemo{
    public static void main(String args[]){
        System.out.printIn(new Book("Java",89.9).getInfo())
    }
}

Obviously, this greatly wastes the number of lines of code, but should Use this to call the constructor method as follows:

class Book{//定義書的類
    private String name;//書本名字
    private int price;//書本價格
    public Book(){//無參構造
        System.out.printIn("*************");
    }
    public Book(String name){//一參構造
        this();//調用本類中的無參構造
        this.name = name;
    }
    public Book(String name,int price){//二參構造
        this(name);//調用本類中的一參構造
        this.price = price;
        }
    public String getInfo(){
        return "書籍：" + name + ",價格：" + price;
    }  

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

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

The most important thing is that calling this 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調用fun方法（this = b1）
        //兩個輸出結果的地址一樣，代表著此時this代表著b1
        System.out.printIn("*************")
        Book b2 = new Book();
        System.out.printIn("MAIN方法"+b2);
        b2.fun();//此時輸出結果和b2一樣
    }
}

Throughout the 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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