Constructor

생성자

• Constructor : Initializing instance method(인스턴스 초기화 메소드!)

: Method that initializes instance(=iv group).

Time t = new Time();
t.hour = 12;
t.minute = 34;
t.second = 56;

Add constructor : To initialize instance(iv group) easily.

Time t = new Time(12,34,56);

class Car {
    String color;
    String gearType;
    int door;
    
    Car() {}//default constructor
    Car(String c, String g, ind d) {
        //iv group
        color = c;
        gearType = g;
        door = d;
    }
}
//1.declare reference type variable
//2.create object using operator new
//3.initialize with calling constructor
Car c = new Car("white","auto",4);

1. constructor name = class name

2. no return value.(no void)

3. All class must have more than one constructor.

class Card {
    ...
    //overlading...
    Card() {//default constructor
        //Initialize instance
    }
    Card(String kind, int number) {
        //Initialize instance
    }
}

• constructor type

1. default constructor

no parameter

when there is no constructor, compiler adds automatically.

class Data_1 {//there is no constructor so compiler adds automatically.
    int value;
    //Data_1(){}
}

class Data_2 {//there is one constructor.
    int value;
    
    //MUST include default constructor manually
    Data_2() {}
    
    Data_2(int x) {
        value = x;
    }
}
class Ex6_11 {
    public static void main(String[] args) {
        Data_1 d1 = new Data_1();//call constructor;
        Data_2 d2 = new Data_2();//call default constructor=>error.cannot resolve symbol : issue with name
        //must add default constructor in Data_2!
    }
}

main class and other method class can be separated like above?