super, super()

reference type variable super, constructor super()

• super

1. reference type variable that indicates itself.

2. exist within instance method(constructor).

3. distinguish parent members between current members

class Parent {int x = 10;}

class Child extens Parent {
    int x = 20;
    
    void omethod() {
        System.out.prinln("x=" - x);
        System.out.prinln("this.x=" + this.x);
        System.out.prinln("super.x=" + super.x);
    }
}

• super() : parent constructor

1. call parent constructor

2. initialize parent member by calling parent constructor

3. add constructor in the first line otherwise compiler adds super(); automatically. 모든 생성자는 첫 줄에 다른 생성자를 호출해야한다. 그렇지 않으면 컴파일러가 자동으로 super()를 호출해버린다.

class Point {
    int x,y;
    
    Point() {
        this(0,0);//constructor in first line
    }
    
    Point(int x, int y) {
        
        this.x = x;
        this.y = y;
    }
}
class Point3D extends Point {
    int z;
    
    Point 3D(int x, int y, int z) {
        super(x,y);
        this.z = z;
    }
}

class Point{
    int x,y;
    
    Point(int x, int y) {
        //no constructor in first line
        //=>compiler will add super();
        this.x = x;
        this.y = y;
    }
}

class Point3D extends Point {
    int z;
    
    Point3D(int x, int y, int z) {
        super(x,y);//call parent constructor super()
        this.z = z;
        //this.x = x;
        //this.y = y;
        
    }
}

right code below :

1. default constructor in Point class

2. must call other constructor in first line

3. super constructor in Point3D constructor

class Point {
    int x;
    int y;
    
    //1. default constructor
    Point() {}
    Point(int x, int y) {
        //2. must call other constructor in first line
        Point(){};
        this.x = x;
        this.y = y;
    }
    
}
class Point3D extends Point {

    int z;
    
    Point3D(int x, int y, int z) {
        
        Point(x,y);
        this.z = z;
    }
    
    
}