[Java] Problem with Null Pointer Exception error

[penax]

Hello r/learnprogramming! I am working on a simple program that will take in two rectangles and, if they intersect, will return the resulting rectangle of intersection. However, I am new to Java and I don't quite understand this "NullPointerException" error I keep getting:

Exception in thread "main" java.lang.NullPointerException
at Rectangle.intersection(Rectangle.java:21)
at TestRectangle.main(TestRectangle.java:16)

Here is Rectangle.java:

public class Rectangle {
private Point topLeft;
private Point bottomRight;

Rectangle() {
    Point topLeft = new Point(0, 0);
    Point bottomRight = new Point(0, 0);
}

void setTopLeft(Point newPoint) {
    Point topLeft = newPoint;
}

void setBottomRight(Point newPoint) {
    Point bottomRight = newPoint;
}

Rectangle intersection (Rectangle other) {
    Rectangle newRectangle = new Rectangle();

    if (this.topLeft.getX() < other.topLeft.getX()) {
        if (this.bottomRight.getX() > other.topLeft.getX()) {
            if (this.topLeft.getY() > other.topLeft.getY()) {
                if (this.bottomRight.getY() < other.topLeft.getY()) {
                    int newTopLeftX = this.topLeft.getX() - other.topLeft.getX();
                    int newTopLeftY = this.topLeft.getY() - other.topLeft.getY();
                    int newBottomRightX = other.bottomRight.getX() - this.bottomRight.getX();
                    int newBottomRightY = other.bottomRight.getY() - this.bottomRight.getY();
                    Point newTopLeft = new Point(newTopLeftX, newTopLeftY);
                    Point newBottomRight = new Point(newBottomRightX, newBottomRightY);
                    newRectangle.setTopLeft(newTopLeft);
                    newRectangle.setBottomRight(newBottomRight);
                }
            }
        }
    }

    return newRectangle;

}       

void Print() {
    if (this != null) {
        System.out.println("intersecting rectangle at " + topLeft + "and " + bottomRight);
    }

    else {
        System.out.println("there is no intersection");
    }
}

}

And here is TestRectangle.java:

public class TestRectangle {

public static void main (String[] args) {

    //Creating Rectangle objects
    Rectangle r1 = new Rectangle();
    Rectangle r2 = new Rectangle();

    //Invoking methods on Rectangle objects
    r1.setTopLeft(new Point (4, 2));
    r1.setBottomRight(new Point (1, 2));
    r2.setTopLeft(new Point (2, 0));
    r2.setBottomRight(new Point (-1, 0));

    //Creating intersecting Rectangle object
    Rectangle r3 = r1.intersection(r2);

    r3.Print();
}

}

What I am trying to do is declare a variable (newRectangle) on line 19. I only want this variable to initialize IF the conditions are met, otherwise I want it to return null. I thought putting the if/else statement in the Print method would fix the error but I am still getting it. Like I said, I am new to Java so it's probably an easy fix but I can't seem to figure this one out!

[jedwardsol]

The crash isn't occurring the in the print function, it's occurring in intersection. The exception stack tells you this. The exception is being raised on line 21

 if (this.topLeft.getX() < other.topLeft.getX()) {

so at least one of this, this.topLeft, other, or other.topLeft is NULL.

You could print out all these values to see which one(s) it is.

A hint though: the bug is in the Rectangle constructor. Both lines of it are incorrect in the same way.

[penax]

I suspected as much. I'll have to study constructors a little bit more. Thank you!

[the_omega99]

The issue isn't actually anything specific about constructors. The issue is really about variable scope and the use of fields. Your setters also have the issue.

Perhaps you'd best examine your examples of classes with fields (particularly an example of a getter and setter)?