面向对象（this关键字）

 1 package com_package2;
 2 
 3 public class Person3 {
 4     private int age;
 5     private String name;
 6     public int getAge() {
 7         return age;
 8     }
 9     public void setAge(int age) {
10         this.age = age;
11     }
12     public String getName() {
13         return name;
14     }
15     public void setName(String name) {
16         this.name = name;
17     }
18     Person3()
19     {
20         System.out.println("hahahaa");
21         
22     }
23     Person3(String n,int a)
24     {
25         name = n;
26         age = a;
27         
28     }
29     Person3(String n)
30     {
31         name = n;
32         
33     }
34     Person3(int a)
35     {
36         
37         age = a;
38     }
39     public void speak()
40     {
41         System.out.println("name = "+name+" "+"age="+age);
42         
43     }
44 }

 1 package com_package2;
 2 
 3 public class Person3Demo {
 4     public static void main(String[]args)
 5     {
 6         Person3 p = new Person3();
 7         p.speak();
 8         Person3 p1 = new Person3("hejinjin",23);
 9         p1.speak();
10         Person3 p2 = new Person3("hejinjin");
11         p2.speak();
12         Person3 p3 = new Person3(23);
13         p3.speak();
14         show();
15             
16     }
17     public static void show()
18     {
19         System.out.println("haha");
20         
21     }
22 
23 }

hahahaa
name = null age=0
name = hejinjin age=23
name = hejinjin age=0
name = null age=23
haha

改成this关键字后：

package com_package2;

public class Person3 {
    private int age;
    private String name;
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    Person3()
    {
        System.out.println("hahahaa");
        
    }
    Person3(String name,int age)
    {
        this.name = name;
        this.age = age;
        
    }
    Person3(String name)
    {
        this.name = name;
        
    }
    Person3(int age)
    {
        
        this.age = age;
    }
    public void speak()
    {
        System.out.println("name = "+this.name+" "+"age="+this.age);
        
    }
}

注意this关键字的格式：this.类中的属性 = 参数中含有的变量

当成员变量和局部变量同名的时候，为了区分，可以使用一个关键字来完成。关键字：this

this：代表的是一个对象，哪个对象调用this所在的函数，this就代表哪个对象，this就是当前对象的一个引用

this什么用：当定义功能的时候，功能内部使用到了调用该功能的对象，这是就用this来表示

this的表现形式一：当局部变量和成员变量同名的时候，可以用this来区分

this的表现形式二：构造函数之间的调用可以使用this关键字，后面跟上小括号，指定其具体的实参即可明确要调用的构造函数

用this关键字进行一般函数调用一般函数：

package com_package2;

public class Person3 {
    private int age;
    private String name;
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    Person3()
    {
        System.out.println("hahahaa");
        
    }
    Person3(String name,int age)
    {   this(name);
        this.name = name;
        this.age = age;
        
    }
    Person3(String n)
    {
        this.name = name;
        
    }
    Person3(int age)
    {
        
        this.age = age;
    }
    public void speak()
    {
        System.out.println("name = "+this.name+" "+"age="+this.age);
        
        
    }
    public void show()
    {
        this.speak();
        
    }
}

package com_package2;

public class Person3Demo {
    public static void main(String[]args)
    {
        Person3 p = new Person3();
        p.speak();
        Person3 p1 = new Person3("hejinjin",23);
        p1.speak();
        Person3 p2 = new Person3("hejinjin");
        p2.speak();
        Person3 p3 = new Person3(23);
        p3.speak();
        p1.show();
            
    }
    

}

利用this关键字进行构造函数和构造函数之间的调用：

package com_package2;

public class Person3 {
    private int age;
    private String name;
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    Person3()
    {  
        System.out.println("hahahaa");
         
    }
    Person3(String name,int age)
    {  // this();
        this.name = name;
        this.age = age;
        
    }
    Person3(String name)
    {
        //this();
        this.name = name;
        
    }
    Person3(int age)
    {
        this("hejinjin",342);
        this.age = age;
    }
    public void speak()
    {
        System.out.println("name = "+this.name+" "+"age="+this.age);
        
        
    }
    public void show()
    {
        this.speak();
        
    }
}

package com_package2;

public class Person3Demo {
    public static void main(String[]args)
    {
        Person3 p = new Person3();
        p.speak();
        Person3 p1 = new Person3("hejinjin",23);
        p1.speak();
        Person3 p2 = new Person3("hejinjin");
        p2.speak();
        Person3 p3 = new Person3(238);
        p3.speak();
        p1.show();
            
    }
    

}

hahahaa
name = null age=0
name = hejinjin age=23
name = hejinjin age=0
name = hejinjin age=238
name = hejinjin age=23

特殊情况：注意：调用本类中的构造函数的this语句必须定义在构造函数的第一行，因为初始化动作要先完成