Java - setXY(x1, y1) 和新的 Object 有什么区别

Question

The problem I'm having is typing x1, x2, y1, y2 into begin and end. This is what I wrote but it did not run as expected.

begin.setXY(x1, y1);
end.setXY(x2, y2);

After reading the answers for this exercise, I found that they used these two lines and it worked. I don't know the difference between these lines of code, please help me !!! And I'm a beginner in java and don't have much experience if you can give me some tips to learn

begin = new Point(x1, y1);
end = new Point(x2, y2);

this is my Point class

public class Point {
    private int x;
    private int y;
    
    public Point () {
        this.x = 0;
        this.y = 0;
    }
    
    public Point (int x, int y) {
        this.x = x;
        this.y = y;
    }

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

    public int getY() {
        return y;
    }

    public void setY(int y) {
        this.y = y;
    }
    
    @Override
    public String toString () {
        return "(" + x + "," + y + ")";
    }
    
    public int[] getXY () {
        int[] array = new int[2];
        array[0] = x;
        array[1] = y;
        return array;
    }
    
    public void setXY (int x, int y) {
        this.x = x;
        this.y = y;
    }
}

and this is my Line class

public class Line {
    private Point begin;
    private Point end;
    
    public Line (int x1, int y1, int x2, int y2) {
//        begin.setXY(x1, y1);
//        end.setXY(x2, y2);
        
        begin = new Point(x1, y1);
        end = new Point(x2, y2);
    }
}

this is my Main class

public class Ex2 {

    public static void main(String[] args) {
        Line a = new Line(1, 2, 3, 4);
        
        System.out.println(a.getBegin());
        System.out.println(a.getEnd());
    }
    
}

Answer 1

Just add the getters and setter in your Line class and you should start getting the values:

public class Line {
    private Point begin;
    private Point end;

    public Line (int x1, int y1, int x2, int y2) {
        begin = new Point(x1, y1);
        end = new Point(x2, y2);
    }
  
    // Just add this
    public Point getBegin() { return begin; }
    public Point getEnd() { return end; }
}