I'm getting a null pointer exception in addPointLoad() method

I have 2 object classes that I am trying to access via this method, but it gives a null-pointer exception. Don't know if it is simply the array size or something more complicated. I was advised to increase the array size the following way (size x 1.5) but am clueless as to how can I do this.

Below is class Beam:

public abstract class Beam {
	private String name;
	protected double length; // [m]
	protected double Emod; // [MPa]
	protected double Ixx; // [m^4]
	private LoadModel loadModel;

	public Beam(String name, double length, double Emod, double Ixx) {
		this.name = name;
		this.length = length;
		this.Emod = Emod;
		this.Ixx = Ixx;
	}
	public void addPointLoad(double magnitude, double loadPos) {
		PointLoad PL = new PointLoad(magnitude, loadPos);
		loadModel.addPL(PL);
	}

The LoadModel class is below:

public class LoadModel {
	private PointLoad[] pointLoads;
	private LineLoad[] lineLoads;
	public int plCounter;
	public int llCounter;

	public LoadModel(PointLoad[] pl, LineLoad[] ll) {
		pointLoads = new PointLoad[2];
		lineLoads = new LineLoad[2];
		plCounter = 0;
		llCounter = 0;
	}

	public void addPL(PointLoad pl) {
		if (plCounter < pointLoads.length) {
			pointLoads[plCounter] = pl;
			plCounter++;
		} else {
			plCounter++;
			pointLoads[plCounter] = pl;
			plCounter++;
		}
		System.out.println("The amount of Point Loads have been increased");
	}

	public int numPL() {  //Added this aswell as I want to keep track of the number of point loads
		return plCounter;
	}

Below is the PointLoad class:

public class PointLoad {
	private double magnitude;
	private double loadPos;
	
	public PointLoad(double magnitude, double loadPos) {
		this.magnitude = magnitude;
		this.loadPos = loadPos;
	}
	
	public double getMag() {
		return magnitude;
	}
	
	public double getLoadPos() {
		return loadPos;
	}
}

Any help will be appreciated.

Add to Beam constructor this line:

loadModel = new LoadModel(null, null);

Uhuh! Your loadModel reference seems to be null in the Beam class. You need to initialize that in either the Beam's constructor.

You declare a member like

private LoadModel loadModel;

and then later you try to call its method like

loadModel.addPL(PL)

which fails due to NullPointerException, because you cannot call a method of that which does not exist. So, to solve your actual problem, you need to initialize loadModel by calling the constructor of LoadModel.

You can instantly know whether the array size is the actual problem, because trying to refer to an element of an array outside of bounds will throw an ArrayIndexOutOfBoundsException, not a NullPointerException.

After you fix your NPE problem now, you might encounter other problems, but let's worry about them when they actually start to cause problems. You can "resize" an array by creating a new array of the desired size of the same type, initializing its elements as you will (by copying the elements of the source) and then assign the new array as the new value of your array variable.