How to define a construct

① The method name is exactly the same as the class name (2) The return value is not described in the method declaration (void is also useless)

Hero class that defines the behavior immediately after birth

public class Hero {
  String name;
  int hp;
  public Hero() {   //Definition of contrast
    this.hp = 100;  //Initialize hp field with 100
  }
}

Method that wrote the process that is automatically executed immediately after being new

Cost Lacta creates a defined Hero

public class Main {
  public static void main(String[] args) {
    Hero h = new Hero();      //100 is assigned to HP at the same time as instant generation
    h.hp = 100;               //I do not need

    System.out.println(h.hp); //Is displayed as 100
  }
}

Receive arguments as additional information in the constructor

public class Hero {
  String name;
  int hp;
  public Hero(String name) {   //Receives one string as an argument
    this.hp = 100;             //Initialize hp field with 100
    this.name = name;          //Initialize the name field with the value of the argument
  }
}

pass arguments with new

public class Main {
  public static void main(String[] args) {
    Hero h = new Hero("Brave");      //After the instant is generated, the JVM automatically executes the constructor as an argument."Brave"Is used

    System.out.println(h.hp);   //Is displayed as 100
    System.out.println(h.name); //Displayed as hero
  }
}

Constructor overload

public class Hero {
  String name;
  int hp;
  public Hero(String name) {   //Constrasta ①
    this.name = name;          
  }
  public Hero() {              //Constructor ②
    this.name = "Brave 2"        //"Brave 2"The set
  }
}

Use of classes overloaded with constasters

public class Main {
  public static void main(String[] args) {
    Hero h = new Hero("Brave");      //Since there is a string argument, the constructor ① is called.
    System.out.println(h.name);    //Displayed as hero

    Hero h2 = new Hero();          //Constructor ② is called because there are no arguments
    System.out.println(h2.name);   //Displayed as Hero 2
  }
}

java (constructor)