我试图通过这个方法访问2个对象类，但是它给出了一个空指针异常。不知道是数组大小还是更复杂。有人建议我按以下方式增加数组大小（大小x1.5），但我不知道如何才能做到这一点。
下面是类梁：

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);
    }

loadmodel类如下：

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;
    }

下面是pointload类：

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;
    }
}

任何帮助都将不胜感激。