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Homework problem:

Add the following constructor to your Line class: public Line(int x1, int y1, int x2, int y2) Constructs the new line that contains the two given points.

My code:

Main Class:

public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.println("Enter x1: ");
        int x01 = scan.nextInt();
        System.out.println("Enter y1: ");
        int y01 = scan.nextInt();
        System.out.println("Enter x2: ");
        int x02 = scan.nextInt();
        System.out.println("Enter y2: ");
        int y02 = scan.nextInt();

        Line object2 = new Line(x01, y01, x02, y02);

        System.out.println(object2);

Point Class: 

private int x;
    private int y;
    private static int count = 0;

    public Point(int x, int y){
        this.x = x;
        this.y = y;
        count++;
    }

    public Point(double x, int y){
        this.x = (int)x;
        this.y = y;
        count++;
    }

    public Point(){
        this(0,0); 
    }

    public String toString(){
        return "(" + x + ", " + y + ")";
    }

    public int getX(){
        return x;
    }

    public void setX(int newX){
        x = newX;
    }

    public int getY(){
        return y;
    }

    public void setY(int newY){
        y = newY;
    }

Line Class:

class Line {

   Point p1;
   Point p2;


    public Line(Point p1, Point p2) {
     this.p1=p1;
     this.p2=p2;

 }

       public Line(int x1, int y1, int x2, int y2) {

    Point p1 = new Point(x1, y1);
    Point p2 = new Point(x2, y2);

    }

    public Point getP1() {
        return p1;
    }
    public Point getP2() {
        return p2;
    }
    public String toString() {
        return "Line points [ (" +p1.getX() + ", "  + p1.getY() + ") , ("+p2.getX() + ", " + p2.getY() + ")]";

}

However, I am still receiving a Null Pointer Exception :

Exception in thread "main" java.lang.NullPointerException
    at assignement05.Line.toString(Line.java:30)
    at java.lang.String.valueOf(String.java:2994)
    at java.io.PrintStream.println(PrintStream.java:821)
at assignement05.Assignement05.main(Assignement05.java:29)
C:\Users\18567\AppData\Local\NetBeans\Cache\8.2\executor-snippets\run.xml:53: Java returned: 1
BUILD FAILED (total time: 4 seconds)

Instead I should receive 

Line Points [ ( x1, y1 ) , (x2, y2) ]

as my output. What is the issue here?

Drake
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  • Your Line constructor, `public Line(int x1, int y1, int x2, int y2) {` is shadowing the p1 and p2 fields. Don't do this. – Hovercraft Full Of Eels Mar 24 '19 at 19:40
  • In other words, don't re-declare the p1 and p2 fields *inside of the constructor*. Change `Point p1 = new Point(x1, y1);` to `p1 = new Point(x1, y1);` -- see the difference? Understand why this matters? In your code your initializing *local* variables leaving the class fields null. – Hovercraft Full Of Eels Mar 24 '19 at 19:41
  • More importantly, learn the general principles of how to debug NPE's as you will encounter these again and again. The answers in the duplicate should help you with this. – Hovercraft Full Of Eels Mar 24 '19 at 19:42
  • @HovercraftFullOfEels Thank you. – Drake Mar 24 '19 at 19:44

0 Answers0