如何移动点并打印新位置？

Question

I'm new to Java and I received an assignment that asks me to write a class called PointerTester that has two Points as instance variables. I need to initialize one of these at coordinate (0.0,0.0) and one at (10.0,12.0). Then I need to move each point by +2.0 in x and -3.0 in Y, query the coordinates of the points, and print out the values.

So far I have this:

public class PointerTester{
/*instance variables*/
    private double pointOneX;
    private double pointOneY;
    private double pointTwoX;
    private double pointTwoY;
    private double deltaX;
    private double deltaY;

    /*constructor to initialize*/
    public PointerTester (){
        pointOneX = 0.0;
        pointOneY = 0.0;
        pointTwoX = 10.0;
        pointTwoY = 12.0;
        deltaX = 2.0;
        deltaY = -3.0;
    }

    /*constructor to initialize to specific value*/
    PointerTester(double pointOneX, double pointOneY, double pointTwoX, double pointTwoY){
        this.pointOneX = pointOneX;
        this.pointOneY = pointOneY;
        this.pointTwoX = pointTwoX;
        this.pointTwoY = pointTwoY;
    }

    /*command to change value*/
    public void moveBy(double deltaX, double deltaY){
        this.pointOneX = this.pointOneX + deltaX;
        this.pointOneY = this.pointOneY + deltaY;
        this.pointTwoX = this.pointTwoX + deltaX;
        this.pointTwoY = this.pointTwoY + deltaY;
    }

    /*Queries*/
    public double getOneX(){
        return pointOneX;
    }
    public double getOneY(){
        return pointOneY;
    }
    public double getTwoX(){
        return pointTwoX;
    }
    public double getTwoY(){
        return pointTwoY;
    }
    /*print values*/
    public static void main(String[] args){
        PointerTester pointOne = new PointerTester();
        PointerTester pointTwo = new PointerTester();
        System.out.println("Point One after move (" + pointOne + ")");
        System.out.println("Point Two after move (" + pointTwo + ")");
    }
}

I cannot figure out how to correctly output the values or if I am completely wrong in working on this problem.

Edit It seems I needed to use this code that I at first thought was supposed to be separate

public class Point{
    public double x;
    public double y;


    public Point(double x, double y){
        this.x = x;
        this.y = y;
    }
    public void setX(double x){
        this.x = x;
    }
    public void setY(double y){
        this.y = y;
    }
    public double getX(){
        return x;
    }
    public double getY(){
        return y;
    }
}

How do I incorporate this into my code?

Answer 1

I think to get started you should have a separate class called "Point" that encapsulates an X and Y value, and includes a "moveBy" method. It could also implement "toString()" such that "System.out.println" will print something nice for it. [Edit: Or just use java.awt.Point.]

Beyond that, I'll leave that for you to do as your homework.

Answer 2

You might want to use some Point objects.

Point p1 = new Point(); Point p2 = new Point(10,12);

you can then use the setLocation or translate methods found in the point class. Maybe the whole thing would look something like this? Hope this helps.

main(){

//make some points
Point p1 = new Point();
Point p2 = new Point(10,12);

//move our points
p1.translate(2,-3);
p2.translate(2,-3);

//print our points
System.out.println(p1);
System.out.println(p2);
}

Answer 3

You can implement the toString method. There are examples here: http://www.javapractices.com/topic/TopicAction.do?Id=55

Answer 4

You're trying to print the PointerTester object instead of the values contained within. System.out.println(pointOne.getOneX()) should at least stop throwing exceptions and allow you to print correctly.