Java泛型-为什么不输出变量？

Question

I've searched and searched, and I feel like I'm missing something really minor about the steps of using them.

Class file for the generic:

public class Point <T> {
    private T xPos, yPos;

    public Point(T xPos, T yPos) {
        this.xPos = xPos;
        this.yPos = yPos;
    }

    public T getXPos() {
        return xPos;
    }

    public void setXPos(T xPos) {
        this.xPos = xPos;
    }

    public T getYPos() {
        return yPos;
    }

    public void setYPos(T yPos) {
        this.yPos = yPos;
    }
}

Demo file:

public class PointTester {
    public static void main(String[] args) {
        Point<Integer> point1 = new Point<Integer>(10,20);
        Point<Double> point2 = new Point<Double>(14.5, 15.6);
        Point<String> point3 = new Point<String>("topleftx", "toplefty");
        System.out.println(point1);
        System.out.println(point2);
        System.out.println(point3);
    }
}

Answer 1

To define how a class in printed, you need to override the standard toString() method. In your example, you'd do something like

public String toString() {
  return "(" + xPos + ", " + yPos + ")";
}

Answer 2

I assume that it is printing 'something' but that the 'something' is un-helpful.

I believe that the thing that you are missing is a 'toString' method.

Answer 3

You need to override the the toString in Point that will return what you want to print.

eg

@Override
public String toString() {
    return /* what you want ... */;
}