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Thread: Problem with NULL.Exception [...]

  1. #1
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    Default Problem with NULL.Exception [...]

    Hello,

    I have got a problem with my code.

    Here are the classes:

    Main.java
    package kompozycja;
     
    public class Main {
    	    public static void main(String[] args) throws Exception {
    	    	Point p1 = new Point(0,0);
    	    	Point p2 = new Point(5,3), p3 = new Point(8,10);
     
    	    	Line l1 = new Line(p1, p2), l2 = new Line(p2, p3);
    	    	Line l3 = new Line(p3, p1), l4 = new Line(p1, p2);
     
    	    	System.out.println(p1.toString());
    	    	System.out.println(p2.toString());
    	    	System.out.println(p3.toString());
     
    	    	System.out.println(l1.toString());
    	    	System.out.println(l2.toString());
    	    	System.out.println(l3.toString());
    	    	System.out.println(l4.toString());
     
    	    	p2.move(5, 6);
     
    	    	System.out.println(p2.toString());
    	    	l1.move(1,2);
    	    	System.out.println(l1.toString());
     
    	    	//Triangle t1 = new Triangle(l1, l2, l3);
    	    	//System.out.println(t1.toString());
    	    	//t1.move(3, 4);
    	    	//System.out.println(t1.toString());
     
    	    	Quadrangle c1 = new Quadrangle(l1, l2, l3, l4);
    	    	c1.move(3, 5);
    	    }
    	}

    Point.java
    // POINT
     
    package kompozycja;
     
    public class Point {
    	private int x, y;
    	// CONSTRUCTOR
    	public Point() {
    		this.x = 0;
    		this.y = 0;
    	}
    	// TWO-PARAMETERS CONSTRUCTOR //
    	public Point(int xx, int yy) {
    		this.x = xx;
    		this.y = yy;
    	}
    	// COPY CONSTRUCTOR //
    	public Point(Point p) {
    		this.x = p.x;
    		this.y = p.y;
    	}
     
    	public void move(int dx, int dy) {
    		this.x = x + dx;
    		this.y = y + dy;
    	}
     
    	public String toString() {
    		return ("("+x+","+y+")");
    	}
     
    	public int getX() {
    		return x;
    	}
     
    	public int getY() {
    		return y;
    	}
    }

    Line.java
    // LINIA
     
    package kompozycja;
     
    public class Line {
    	private Point start, end;
    		// CONSTRUCTOR //
    	public Line() {
    		Point start = new Point();
    		Point end = new Point();
    	}
    		// TWO-PARAMETERS CONSTRUCTOR //
    	public Line(Point start, Point end) {	
    			this.start = new Point(start);
    			this.end = new Point(end);
    	}
    		// COPY CONSTRUCTOR //
    	public Line(Line line){
    			line.start = new Point(line.getStart());
    			line.end = new Point(line.getEnd());
    	}
     
    	public void move(int dx, int dy) {
    			start.move(dx, dy);
    			end.move(dx, dy);
    	}
     
    	public String toString() {
    			return start.toString() + "->" + end.toString();
    	}
     
    	public Point getStart() {
    		return start;
    	}
     
    	public Point getEnd() {
    		return end;
    	}
    }

    Triangle.java
    package kompozycja;
     
    public class Triangle {
    		private Line line1, line2, line3;
    			// CONSTRUCTOR //
    		public Triangle() {
    			this.line1 = new Line();
    			this.line2 = new Line();
    			this.line3 = new Line();
    		}
    			// COPY CONSTRUCTOR //
    		public Triangle(Triangle trojkat) {
    			this.line1 = new Line(trojkat.getL1());
    			this.line2 = new Line(trojkat.getL2());
    			this.line3 = new Line(trojkat.getL3());
    		}
    			// THREE-PARAMETERS CONSTRUCTOR //
    		public Triangle(Line linia1, Line linia2, Line linia3){
    			this.line1 = new Line(linia1);
    			this.line2 = new Line(linia2);
    			this.line3 = new Line(linia3);
    		}
     
    		public void move(int dx, int dy) {
    			line1.move(dx, dy);
    			line2.move(dx, dy);
    			line3.move(dx, dy);
    		}
     
    		public String toString() {
    			return line1.toString() + "\n" + line2.toString() + "\n" + line3.toString();
    		}
     
    		public Line getL1() {
    			return line1;
    		}
     
    		public Line getL2() {
    			return line2;
    		}
     
    		public Line getL3() {
    			return line3;
    		}
    }

    Quadrangle.java
    package kompozycja;
     
    public class Quadrangle {
    	private Line line1, line2, line3, line4;
    		// CONSTRUCTOR //
    	public Quadrangle() {
    		this.line1 = new Line();
    		this.line2 = new Line();
    		this.line3 = new Line();
    		this.line4 = new Line();
    	}
    		// COPY CONSTRUCTOR //
    	public Quadrangle(Quadrangle quadrangle) {
    		this.line1 = new Line(quadrangle.getL1());
    		this.line2 = new Line(quadrangle.getL2());
    		this.line3 = new Line(quadrangle.getL3());
    		this.line4 = new Line(quadrangle.getL4());
    	}
    		// PARAMETERS CONSTRUCTOR //
    	public Quadrangle(Line line1, Line line2, Line line3, Line line4){
    		this.line1 = new Line(line1);
    		this.line2 = new Line(line2);
    		this.line3 = new Line(line3);
    		this.line4 = new Line(line4);
    	}
     
    	public void move(int dx, int dy) {
    		line1.move(dx, dy);
    		line2.move(dx, dy);
    		line3.move(dx, dy);
    		line4.move(dx, dy);
    	}
     
    	public String toString() {
    		return line1.toString() + "\n" + line2.toString() + "\n" + line3.toString() + "\n" + line4.toString();
    	}
     
    	public Line getL1() {
    		return line1;
    	}
     
    	public Line getL2() {
    		return line2;
    	}
     
    	public Line getL3() {
    		return line3;
    	}
    		// ZWRACA LINIE linia4 //
    	public Line getL4() {
    		return line4;
    	}
    }

    Picture.java
    package kompozycja;
     
    public class Picture {
    	private Triangle triangle;
    	private Quadrangle quadrangle;
    	private Triangle[] picture1 = new Triangle[20];
    	private Quadrangle[] picture2 = new Quadrangle[20];
     
    		// CONSTRUCTOR //
    	public Picture() {
    		for(int i=0; i<20; i++) {
    			picture1[i] = null;
    			picture2[i] = null;
    		}
    	}
    		// ADD TRIANGLE TO TAB //
    	public void add_triangle(Triangle triangle) {
    		for(int i=0; i<20; i++) {
    			if(picture1[i] == null) {
    				picture1[i] = triangle;
    				break;
    			}
    		}
    	}
    		// ADD QUADRANGLE TO TAB //
    	public void add_quadrangle(Quadrangle quadrangle) {
    		for(int i=0; i<20; i++) {
    			if(picture2[i] == null) {
    				picture2[i] = quadrangle;
    				break;
    			}
    		}
    	}
    }




    The compilator says:
    (0,0)
    (5,3)
    (8,10)
    (0,0)->(5,3)
    (5,3)->(8,10)
    (8,10)->(0,0)
    (0,0)->(5,3)
    (10,9)
    (1,2)->(6,5)
    Exception in thread "main" java.lang.NullPointerException
    	at kompozycja.Line.move(Line.java:24)
    	at kompozycja.Quadrangle.move(Quadrangle.java:28)
    	at kompozycja.Main.main(Main.java:32)

    How can I fix it?

    Thanks for all your answers.


  2. #2
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    Default Re: Problem with NULL.Exception [...]

    This is a Null Pointer Exception or NPE. Something in the Line.move() method is null. I can't be sure, but I suspect line 24 of the Line class includes the move() method,
        public void move(int dx, int dy)
        {
            start.move(dx, dy);
            end.move(dx, dy);
        }
    It seems that either start or end must be null. Add print statements or do a code inspection to determine why start and/or end may not have been initialized.

  3. The Following User Says Thank You to GregBrannon For This Useful Post:

    fkmk (April 27th, 2014)

  4. #3
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    Default Re: Problem with NULL.Exception [...]

    Quote Originally Posted by GregBrannon View Post
    This is a Null Pointer Exception or NPE. Something in the Line.move() method is null. I can't be sure, but I suspect line 24 of the Line class includes the move() method,
        public void move(int dx, int dy)
        {
            start.move(dx, dy);
            end.move(dx, dy);
        }
    It seems that either start or end must be null. Add print statements or do a code inspection to determine why start and/or end may not have been initialized.
    Thank you! Thanks for your advice, I fixed it.
    The problem occured in a Line copy Constructor:

    Fixed code:
     	public Line(Line line){
    	start = new Point(line.getStart());
    	end = new Point(line.getEnd());
    	}

  5. #4
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    Default Re: Problem with NULL.Exception [...]

    You're welcome, glad to help.

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