Question

我在这里引用了一些修正，但仍然完全满足我的程序，但仍然没有完成问题1 =我的displayReg（）出来＆＃34; nullnullnullnull ...＆＃34; ，我应该使用arraylist吗？问题2 =我需要选择通过IC和NAME搜索searchReg（）我该怎么做？问题3 =需要在.txt文件上显示displayReg。

import java.util.*;
public class RegisterMenu {
    private Driver[] newOwner;
    private final int MAX_ITEMS = 10;
    private int size = 0;

    public Driver newReg(){
        Driver owner = new Driver();
        Scanner scan = new Scanner(System.in);
        owner.setRegNo(size+1);
        System.out.print("Enter Name: ");
        owner.setName(scan.nextLine());
        System.out.print("Enter IC: ");
        owner.setIc(scan.nextLine());
        System.out.print("Enter PlateNo: ");
        owner.carInfo.setPlateNum(scan.nextLine());
        System.out.print("Enter Color: ");
        owner.carInfo.setColor(scan.nextLine());
        System.out.print("Enter Year: ");
        owner.carInfo.setYear(scan.nextLine());
        System.out.print("Enter Make: ");
        owner.carInfo.setMake(scan.nextLine());
        System.out.print("Enter Model: ");
        owner.carInfo.setModel(scan.nextLine());
        System.out.print("Enter Capacity: ");
        owner.carInfo.setCapacity(scan.nextLine());
        return owner;

    }
    public Driver editReg(){
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter RegNo to be edit: ");
        int input = scan.nextInt();
        Driver owner = newReg();
        newOwner[input] = owner;

        return owner;
    }
    public Driver searchReg(){

    }
    public void displayReg(){
     for(int i = 0; i < newOwner.length; i++){
         newOwner[i].toString();
     }    
    }



    public RegisterMenu(){
        newOwner = new Driver[MAX_ITEMS];
        Scanner scan = new Scanner(System.in);
        System.out.println("1. Register New Car");
        System.out.println("2. Edit Car Information");
        System.out.println("3. Search Car Information");
        System.out.println("4. Display Car List");
        System.out.println("5. Exit");
        System.out.print("Enter Selection: ");
        int s = scan.nextInt();
        switch(s){
            case 1:
                System.out.println("--Register New Car--");
                if (size < MAX_ITEMS) {
                Driver owner = newReg();
                newOwner[size++] = owner;
                }
                break;
            case 2:
                System.out.println("--Edit Car Infomation--");
                editReg();

                break;
            case 3:
                System.out.println("--Search Car Infomation--");
                break;
            case 4:
                System.out.println("--Display Car Infomation--");
                displayReg();
                break;

            case 5:
                System.exit(0);
            default:
                System.out.println("Error selection");



        }

    }
    public static void main (String args[]){
        while(true){
            RegisterMenu owner = new RegisterMenu();

        }
    }


}

这是我的Car class

public class Car {

    public String plateNum;
    public String make;
    public String model;
    public String color;
    public String year;
    public String capacity;

    public Car(){

    }

    public Car(String plateNum, String color, String year, String make, String model, String capacity){
        this.plateNum = plateNum;
        this.color = color;
        this.year = year;
        this.make = make;
        this.model = model;
        this.capacity = capacity;
    }
    public String getPlateNum(){
        return plateNum;
    }
    public String getMake(){
        return make;
    }
    public String getModel(){
        return model;
    }
    public String getColor(){
        return color;
    }
    public String getYear(){
        return year;
    }
    public String getCapacity(){
    return capacity;
    }
    public void setPlateNum(String plateNum){
        this.plateNum = plateNum;
    }
    public void setMake(String make){
        this.make = make;
    }
    public void setModel(String model){
        this.model = model;
    }
    public void setColor(String color){
        this.color = color;
    }
    public void setYear(String year){
        this.year = year;
    }
    public void setCapacity(String capacity){
        this.capacity = capacity;
    }




}

这是我的Driver类

public class Driver {
   private int regNo;
   private String name;
   private String ic;
   Car carInfo = new Car();

   public Driver(){

   }
   public Driver(int regNo, String name, String ic, Car carInfo){
       this.regNo = regNo;
       this.name = name;
       this.ic = ic;
       this.carInfo = carInfo;
   }
   public int getRegNo(){
       return regNo;
   }
   public String getName(){
       return name;
   }
   public String getIc(){
       return ic;
   }
   public void setRegNo(int regNo){
       this.regNo = regNo;
   }
   public void setName(String name){
       this.name = name;
   }
   public void setIc(String ic){
       this.ic = ic;
   }
   public String toString(){
       return "RegNo: "+getRegNo()+"\tName: "+getName()+"\tIc: "+getIc()+
               "\tPlateNo: "+carInfo.getPlateNum()+"\tColor: "+carInfo.getColor()+"\tYear: "+carInfo.getYear()+
                       "\tMake: "+carInfo.getMake()+"\tModel: "+carInfo.getModel()+"\tCapacity: "+carInfo.getCapacity();
   }

}

Answer 1

Register[] a = new Register[i]; -创建一个包含0个项目的数组。

a[i].Reg(); - 访问没有任何项目的数组的位置0。

这是tutorial

Answer 2

int i = 0;
Register[] a = new Register[i];

您正在尝试创建0大小的数组。但是当你尝试在i = 0时访问[i]时，它会尝试访问数组中第1个位置的元素（数组的第一个位置为0）。

此外，您已将其置于while循环中，这意味着您在每个循环周期中创建一个0大小的新数组。

尝试将i = 10（或您的程序逻辑所说的任何内容）并将数组创建放在循环中

在数组中输入数据并显示null时出现程序错误

2 个答案: