This 在构造函数中的固定用法

class Person{
  String name;
  int age;
  char gender;
  public Person (String name){
     this.name = name;
  }
   public Person (String name , int age){
     this.name = name;
     this.age = age;
  }
  public Person (String name , int age ,char gender){
     this.name = name;
     this.age = age;
     this.gender = gender;
  }  

  public void introduce(){
    System.out.println("我是"+name+"     今年"+age+"岁     性别： "+gender);
  }
}

　　

和下面的代码相同

class Person{
  String name;
  int age;
  char gender;
  public Person (String name){
     this.name = name;
  }
   public Person (String name , int age){
     this(name);//调用只有一个参数的构造函数（必须是此构造函数里的第一行）
     this.age = age;
  }
  public Person (String name , int age ,char gender){
     this(name,age);//调用有两个参数的构造函数（必须是此构造函数里的第一行）
     this.gender = gender; 
  }
 public void introduce(){ 
    System.out.println("我是"+name+" 今年"+age+"岁 性别： "+gender); 
 } 
}