Java - Error initialising Object Array List

Question

I am getting a null pointer exception when I try to use the perimeter function in my code. It seems that the Points array (Point is a simple object with an x and y coordinate) is not correctly initialising, I believe I may have declared the array wrongly or the constructor is incorrect.

package shapes;

import static java.lang.Math.*;

public class Triangle {

private int sides = 3;
private Point[] Points = new Point[sides];

public Triangle(Point[] vertices) {
    vertices = Points;
}

public double perimeter() {
    return Points[0].distance(Points[1]) + Points[1].distance(Points[2]) + Points[2].distance(Points[0]);
}

public double area() {
    double semiperimeter = perimeter() / 2;
    return sqrt(semiperimeter * (semiperimeter - Points[0].distance(Points[1])) * (semiperimeter - Points[1].distance(Points[2])) * (semiperimeter - Points[2].distance(Points[0])));
}

@Override
public String toString() {
    return "Triangle has perimeter of " + perimeter() + " and an area of " + area(); 
}

public void translate(int dx, int dy) {
    for(int i = 0; i < 3; i++) {
        Points[i].translate(dx, dy);
    }
}

public void scale(int factor) {
    for(int i = 0; i < 3; i++) {
        Points[i].scale(factor);
    }        
}

public Point getVertex(int i) {
    return Points[i];
}

}

Any help is much appreciated!

You're initializing the array. Are you initializing its elements? — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Mar 31, 2014 at 2:20

Juned Ahsan · Accepted Answer · 2014-03-31 02:21:05Z

6

You need to reverse this in your constructor:

vertices = Points;

to

Points = vertices ;

You need to initialize your Points array with the input vertices and not the other way around.

answered Mar 31, 2014 at 2:21

Juned Ahsan

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2 Comments

h1h1 Over a year ago

So simple, you got it! Thanks haha

Juned Ahsan Over a year ago

@h1h1 it happens..just accept the answer if it helped!

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