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java - 我在 addPointLoad() 方法中遇到空指针异常

问题描述

我有 2 个我试图通过此方法访问的对象类，但它给出了一个空指针异常。不知道是简单的数组大小还是更复杂的东西。有人建议我按照以下方式增加数组大小（大小 x 1.5），但我不知道该怎么做。

下面是 Beam 类：

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;
    }
}

任何帮助将不胜感激。

标签： javaarraysobjectnullpointerexception

解决方案

将此行添加到 Beam 构造函数：

loadModel = new LoadModel(null, null);

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