如何使用无参数构造函数来保存数组对象而不使用nullpointerexception

Question

我创建了一个Auto类，它包含一个OptionSet数组类（即Color，Transmission），它连接到一个包含Options数组内部类（即Blue，Red）的OptionSet类。我计划逐行读取文本文件并用它填充Auto对象。但是，我不知道如何使用在读取文件时定义的OptionSet数组创建Auto对象，而不会出现NullPointerException。

根据我的理解，我不应该使用特定的构造函数，因为数组长度将变得不可更改，使得阅读其他大小的文件变得困难。但是使用默认构造函数意味着optionSet和Option对象中的数组未初始化并导致NullPointerErrors。 （我知道arrayList是构建它的另一种选择，我们将使用它;这是一个在构建产品的过程中遇到常见错误的类项目。）有没有解决这个问题的方法，或者别的我我失踪了？

这是我的错误代码：

Exception in thread "main" java.lang.NullPointerException
    at model.Automotive.setOptionSetName(Automotive.java:61)
    at util.FileInput.readData(FileInput.java:32)
    at driver.Driver.main(Driver.java:17)

自动课程：

package model;

import java.io.*;
import java.io.Serializable;

import model.OptionSet;
import model.OptionSet.Option;
import util.FileInput;

public class Automotive implements Serializable{

//variables
private String name;
private static float basePrice;
private OptionSet[] opSet;

//constructor
public Automotive(int size, String n, float price) {
    opSet = new OptionSet[size];
    name = n;
    basePrice = price;
    for(int i=0; i<opSet.length; i++) {
        opSet[i] = new OptionSet();
    }
}

public Automotive() {
}

public void createOptionsSet(int opSetSize) {
    this.opSet = new OptionSet[opSetSize];  
}

public void createOption(int opSetLocation, int size) {
    this.opSet[opSetLocation].createOption(size);
}

public void setName(String newName) {
    name = newName;
}

public String getName() {
    return name;
}

public void setPrice(float price) {
    basePrice = price;
}

public float getPrice() {
    return basePrice;
}

public OptionSet getOptionSet(int location) {
    return opSet[location];
}

public void setOptionSetName(int opSetLocation, String opSetName) {
    this.opSet[opSetLocation].setOptionSetName(opSetName);
}   

public String getOptionSetName(int opSetLocation) {
    return this.opSet[opSetLocation].getOptionSetName();
}

public void setOption(int opSetLocation, int opLocation, String name, float price) {
    this.opSet[opSetLocation].setOption(opLocation, name, price);
}

public Option getOption(int opSetLocation, int opLocation) {
    return this.opSet[opSetLocation].getOption(opLocation);
}
}

optionSet类（带内部类Option）

package model;

import java.io.Serializable;
import java.util.Arrays;

import model.OptionSet;

public class OptionSet implements Serializable{
//variables
private OptionSet[] opSet;
private Option opt[];
private String name;

//constructor
protected OptionSet(String n, int size) {
    opt = new Option[size];
    name = n;
    for(int i=0; i<opt.length; i++) {
        opt[i] = new Option();
    }
}

public OptionSet() {
}

//methods
protected void createOptionsSet(int size) {
    OptionSet[] opSet = new OptionSet[size];//creates OptionSet array
}

protected void createOption(int size) {
    this.opt = new Option[size];
}

protected void setOptionSetName(String newNname) {
    name = newNname; //to name the optionSet cells - color, transmission, etc
}

protected String getOptionSetName() {
    return name;
}


protected void setOption(int location, String newName, float newPrice) {
    this.opt[location].setName(newName);
    this.opt[location].setPrice(newPrice);
}

protected Option getOption(int location) {
    return this.opt[location];
}

protected void setOptionName(int location, String newName) {
    this.opt[location].setName(newName);
}

protected String getOptionName(int location) {
    return this.opt[location].name;
}

protected void setOptionPrice(int location, float newPrice) {
    this.opt[location].setPrice(newPrice);
}

protected float getOptionPrice(int location) {
    return this.opt[location].price;
}

protected void deleteOption(int location) {
    this.opt[location].deleteOption();
}

protected void deleteOptionName(int location) {
    this.opt[location].deleteName();
}

protected void deleteOptionPrice(int location) {
    this.opt[location].deletePrice();
}

//does this work to print a custom object?
protected void print(Automotive auto) {
    System.out.printf("%10s", name);
    for(int j=0; j<opt.length; j++) {
        this.opt[j].print(auto);
    }
}

//inner class Option
protected class Option implements Serializable{
    private String name;
    private float price;

    Option(String name, float price){
        name = name;
        price = price;
    }

    public Option() {
    }

    protected void print(Automotive auto) {
        System.out.printf("%10s", name);
        System.out.printf("%10f", price);
    }

    protected void createOption(String name, float price) {
        Option opt = new Option(name, price);
    }

    protected void setName(String newName) {
        name = newName;
    }

    protected String getName() {
        return name;
    }

    protected void setPrice(float newPrice) {
        price = newPrice;
    }

    protected float getPrice() {
        return price;
    }

    protected void updateName(String newName) {
        name = newName;
    }

    protected void updatePrice(float newPrice) {
        price = newPrice;
    }
}

FileInput类，使用公共自动方法：

package util;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.StringTokenizer;

import model.*;

public class FileInput {
    public Automotive readData(String fileName){
        //houses parser
        Automotive auto = new Automotive();
//      auto.createOptionsSet(5);


        try {
            FileReader file = new FileReader(fileName);
            BufferedReader buff = new BufferedReader(file);
            String name = buff.readLine(); //Focus Wagon ZTW
            auto.setName(name);
            String price = buff.readLine(); //18445
            auto.setPrice(Integer.parseInt(price));
            int opSetSize = Integer.parseInt(buff.readLine()); //5
            auto.createOptionsSet(opSetSize); //create optionSet of size 5
            for(int opSetLocation=0; opSetLocation < opSetSize; opSetLocation++) {
                String optionTitle = buff.readLine(); //Color
                auto.setOptionSetName(opSetLocation, optionTitle);
                int opSize = Integer.parseInt(buff.readLine()); //10
                //optionsettotal, in each option set option array of size blah
                auto.createOption(opSetLocation, opSize);
                for (int opLocation=0; opLocation < opSize; opLocation++) { //loop to parse colors
                    String optionLine = buff.readLine(); //get first color, "gold, 0"
                    StringTokenizer st = new StringTokenizer(optionLine, ", ");
                    String optionName = st.nextToken();
                    float optionPrice = Float.parseFloat(st.nextToken());
                    auto.setOption(opSetLocation, opLocation, optionName, optionPrice);
                }
            }
        buff.close();   
        }
        catch (IOException e) {
            System.out.println("Error -- " + e.toString());
        }
        return auto;
    }

    public void serializeAuto(Automotive auto) 
    {
        try {
            ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("auto.ser"));
            out.writeObject(auto);
            out.flush();
            out.close();
        } catch (IOException e) {
            System.out.print("Error: " + e);
            System.exit(1);
        }
    }

    public Automotive deserializeAuto(String fileName) {
        Automotive newAuto = null;
        try {
            ObjectInputStream in = new ObjectInputStream(new FileInputStream(fileName));
            newAuto = (Automotive) in.readObject();
        }
        catch(IOException e) {
            System.out.print("Error: " + e);
            System.exit(1);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    return newAuto;
    }
}

用于运行实际程序的Driver类：

package driver;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

import model.Automotive;
import util.FileInput;

public class Driver{

    public static void main(String[] args) {
        //Build Automotive object from a file
        FileInput file = new FileInput();
        Automotive FordZTW = file.readData("C:\\Users\\~ Adam ~\\Documents\\Computer Programming Notes\\Advanced Problem Solving\\FordZTW.txt");
        //print attributes before serialization
        FordZTW.printAuto(FordZTW);
        //Serialize object
        file.serializeAuto(FordZTW);
        //Deserialize the object and read it into memory
        Automotive newFordZTW = file.deserializeAuto("auto.ser");
        //print new attributes
        newFordZTW.printAuto(FordZTW);
    }
}