Thread: 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.

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.

Originally Posted by GregBrannon

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());
	}

You're welcome, glad to help.