Java数组搜索和排序未按预期工作

我目前正在介绍Java类，我们目前讨论的是数组主题。我们有一个类实验室，假设在这里创建一个简单的数组程序，它由两个类组成（Passenger.java和Demo.java）。数组可以是任意大小（最小4个），我们可以将细节硬编码为几个元素。我们应该创建两个按ID和姓名搜索的方法（firstname+lastname），以及两个按ID和姓氏升序排序的方法（冒泡和插入）

在我的ID和名称搜索方法中，当我输入一个数组中不存在的ID时，得到java.lang.NullPointerException错误。如果找不到，它应该返回我编写的错误消息

在ID的排序方法中，在第二个循环之后，我还得到java.lang.NullPointerException错误。对于我的姓氏排序方法，我不知道如何实现

因此，我想知道如何通过一个完整的代码示例来解决这两个问题

注:

• 我不能使用ArrayList和任何Java数组类
• 请将数组的元素3到8视为已用值初始化
• 我看过这个，这个，还有这个，最后还有这个

Passenger.java

import java.util.Scanner;

public class Passenger {

    private String title;
    private String firstName;
    private String lastName;
    private long id;

    public Passenger() {

    }

    public Passenger(String title, String firstName, String lastName, long id) {
        this.title = title;
        this.firstName = firstName;
        this.lastName = lastName;
        this.id = id;
    }

    public void enterDetails() {
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Enter your title: ");
        title = keyboard.next();
        System.out.print("Enter your first name: ");
        firstName = keyboard.next();
        System.out.print("Enter your last name: ");
        lastName = keyboard.next();
        System.out.print("Enter your ID: ");
        id = keyboard.nextLong();
    }

    public void outputDetails() {
        System.out.print();
        System.out.print("Passenger name: " + title + " " + firstName + " " + lastName);
        System.out.print("Identify Number: " + id);
        System.out.print();
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public long getId() {
        return id;
    }

}

import java.util.Scanner;

public class Demo {

    public static Passenger[] passengers = new Passenger[10];
    public static Scanner kb = new Scanner(System.in);

    public static void main(String[] args) {

        int option = 0;

        passengers[0] = new Passenger("Mr", "Benjamin", "Parker", 12345678);
        passengers[1] = new Passenger("Mrs", "Mary", "Long", 96421368);
        passengers[2] = new Passenger(....);
        passengers[3] = new Passenger(....);
        passengers[4] = new Passenger(....);
        passengers[5] = new Passenger(....);
        passengers[6] = new Passenger(....);
        passengers[7] = new Passenger(....);

        while(option != 7) {
            System.out.println("Please select an option:"
                + "\n1) Enter passenger particulars to array"
                + "\n2) Display passenger particulars from array"
                + "\n3) Search passenger particulars using ID"
                + "\n4) Search passenger particulars using both surname and name"
                + "\n5) Display passenger particulars in ascending order of ID"
                + "\n6) Display passenger particulars in ascending order of surname"
                + "\n7) Quit
            )
            option = kb.nextInt();

            switch(option) {
                case 1:
                    inputDetails();
                    break;
                case 2:
                    outputDetails();
                    break;
                case 3:
                    searchDetailsID();
                    break;
                case 4:
                    searchDetailsName();
                    break;
                case 5:
                    sortDetailsID();
                    break;
                case 6:
                    sortDetailsName();
                    break;
                case 7:
                    System.out.println("You quitted the program!");
                    break;
                default:
                    System.out.println("Invalid input!");
                    break;
            }
        }
    }

    public static void inputDetails() {
        int element = 0;
        for (int i = 0; i < passengers.length; i++) {
            if(passengers[i] != null)
                element++;
        }
        passengers[element] = new Passenger();
        passengers[element].enterDetails();
        element++;
    }

    public static void outputDetails() {
        for(int i = 0; i < passengers.length; i++) {
            passengers[i].outputDetails();
        }
    }

    public static void searchDetailsID() {
        boolean isFound = false;
        System.out.print("Please enter an passenger id: ");
        long id = kb.nextLong();

        for(int i = 0; i < passengers.length; i++) {
            if(id == passengers[i].getid()) {
                passengers[i].outputDetails();
                isFound = true;
                break;
            }
        }

        if(!isFound) {
            System.out.println("No passenger with that id!");
        }
    }

    public static void searchDetailsName() {
        boolean isFound = false;
        System.out.print("Please enter an passenger first name: ");
        String firstName = kb.next();
        System.out.print("Please enter an passenger last name: ");
        String lastName = kb.next();

        for(int i = 0; i < passengers.length; i++) {
            if(firstName.equalsIgnoreCase(passengers[i].getFirstName()) && lastName.equalsIgnoreCase(passengers[i].getLastName())) {
                passengers[i].outputDetails();
                isFound = true;
                break;
            }
        }

        if(!isFound) {
            System.out.println("No passenger with that name!");
        }
    }

    public static void sortDetailsID() {
        long temp = 0;
        for(int i = 0; i < passengers.length; i++) {
            for(int j = 0; j < passengers.length - 1; j++) {
                if(passengers[i].getId() > passengers[j].getId()) {
                    temp = passengers[i].getId();
                    passengers[i] = passengers[j];
                }
            }
        }
    }

    public static void sortDetailsName() {

    }

}

Demo.java

import java.util.Scanner;

public class Passenger {

    private String title;
    private String firstName;
    private String lastName;
    private long id;

    public Passenger() {

    }

    public Passenger(String title, String firstName, String lastName, long id) {
        this.title = title;
        this.firstName = firstName;
        this.lastName = lastName;
        this.id = id;
    }

    public void enterDetails() {
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Enter your title: ");
        title = keyboard.next();
        System.out.print("Enter your first name: ");
        firstName = keyboard.next();
        System.out.print("Enter your last name: ");
        lastName = keyboard.next();
        System.out.print("Enter your ID: ");
        id = keyboard.nextLong();
    }

    public void outputDetails() {
        System.out.print();
        System.out.print("Passenger name: " + title + " " + firstName + " " + lastName);
        System.out.print("Identify Number: " + id);
        System.out.print();
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public long getId() {
        return id;
    }

}

import java.util.Scanner;

public class Demo {

    public static Passenger[] passengers = new Passenger[10];
    public static Scanner kb = new Scanner(System.in);

    public static void main(String[] args) {

        int option = 0;

        passengers[0] = new Passenger("Mr", "Benjamin", "Parker", 12345678);
        passengers[1] = new Passenger("Mrs", "Mary", "Long", 96421368);
        passengers[2] = new Passenger(....);
        passengers[3] = new Passenger(....);
        passengers[4] = new Passenger(....);
        passengers[5] = new Passenger(....);
        passengers[6] = new Passenger(....);
        passengers[7] = new Passenger(....);

        while(option != 7) {
            System.out.println("Please select an option:"
                + "\n1) Enter passenger particulars to array"
                + "\n2) Display passenger particulars from array"
                + "\n3) Search passenger particulars using ID"
                + "\n4) Search passenger particulars using both surname and name"
                + "\n5) Display passenger particulars in ascending order of ID"
                + "\n6) Display passenger particulars in ascending order of surname"
                + "\n7) Quit
            )
            option = kb.nextInt();

            switch(option) {
                case 1:
                    inputDetails();
                    break;
                case 2:
                    outputDetails();
                    break;
                case 3:
                    searchDetailsID();
                    break;
                case 4:
                    searchDetailsName();
                    break;
                case 5:
                    sortDetailsID();
                    break;
                case 6:
                    sortDetailsName();
                    break;
                case 7:
                    System.out.println("You quitted the program!");
                    break;
                default:
                    System.out.println("Invalid input!");
                    break;
            }
        }
    }

    public static void inputDetails() {
        int element = 0;
        for (int i = 0; i < passengers.length; i++) {
            if(passengers[i] != null)
                element++;
        }
        passengers[element] = new Passenger();
        passengers[element].enterDetails();
        element++;
    }

    public static void outputDetails() {
        for(int i = 0; i < passengers.length; i++) {
            passengers[i].outputDetails();
        }
    }

    public static void searchDetailsID() {
        boolean isFound = false;
        System.out.print("Please enter an passenger id: ");
        long id = kb.nextLong();

        for(int i = 0; i < passengers.length; i++) {
            if(id == passengers[i].getid()) {
                passengers[i].outputDetails();
                isFound = true;
                break;
            }
        }

        if(!isFound) {
            System.out.println("No passenger with that id!");
        }
    }

    public static void searchDetailsName() {
        boolean isFound = false;
        System.out.print("Please enter an passenger first name: ");
        String firstName = kb.next();
        System.out.print("Please enter an passenger last name: ");
        String lastName = kb.next();

        for(int i = 0; i < passengers.length; i++) {
            if(firstName.equalsIgnoreCase(passengers[i].getFirstName()) && lastName.equalsIgnoreCase(passengers[i].getLastName())) {
                passengers[i].outputDetails();
                isFound = true;
                break;
            }
        }

        if(!isFound) {
            System.out.println("No passenger with that name!");
        }
    }

    public static void sortDetailsID() {
        long temp = 0;
        for(int i = 0; i < passengers.length; i++) {
            for(int j = 0; j < passengers.length - 1; j++) {
                if(passengers[i].getId() > passengers[j].getId()) {
                    temp = passengers[i].getId();
                    passengers[i] = passengers[j];
                }
            }
        }
    }

    public static void sortDetailsName() {

    }

}

import java.util.Scanner；
公开课演示{
公共静态乘客[]乘客=新乘客[10]；
公共静态扫描仪kb=新扫描仪（System.in）；
公共静态void main（字符串[]args）{
int选项=0；
乘客[0]=新乘客（“先生”、“本杰明”、“帕克”，12345678）；
乘客[1]=新乘客（“夫人”、“玛丽”、“朗”，96421368）；
乘客[2]=新乘客（……）；
乘客[3]=新乘客（……）；
乘客[4]=新乘客（……）；
乘客[5]=新乘客（……）；
乘客[6]=新乘客（……）；
乘客[7]=新乘客（……）；
while（选项！=7）{
System.out.println（“请选择一个选项：”
+“\n1）将乘客详细信息输入数组”
+“\n2）显示来自数组的乘客详细信息”
+“\n3）使用ID搜索乘客详细信息”
+“\n4）使用姓氏和姓名搜索乘客详细信息”
+“\n5）按ID的升序显示乘客详细信息”
+“\n6）按姓氏升序显示乘客详细信息”
+“\n7）退出
)
option=kb.nextInt（）；
开关（选件）{
案例1：
inputDetails（）；
打破
案例2：
outputDetails（）；
打破
案例3：
searchDetailsID（）；
打破
案例4：
searchDetailsName（）；
打破
案例5：
sortDetailsID（）；
打破
案例6：
sortDetailsName（）；
打破
案例7：
System.out.println（“你退出了这个程序！”）；
打破
违约：
System.out.println（“无效输入！”）；
打破
}
}
}
公共静态无效inputDetails（）{
int元素=0；
对于（int i=0；i乘客[j].getId（））{
temp=乘客[i].getId（）；
乘客[i]=乘客[j]；
}
}
}
}
公共静态无效sortDetailsName（）{
}
}

您的NPE堆栈跟踪是：

Exception in thread "main" java.lang.NullPointerException
    at com.Demo.searchDetailsID(Demo.java:90)
    at com.Demo.main(Demo.java:46)

如果您深入评估代码，您会发现您使用10初始化了

passengers

数组，但您只在

Demo

类的

main

方法中引用了8索引。换句话说，当您的循环想要从t中读取9或10索引时，会抛出NPE他用了一个数组。 因此，如果您替换

Demo的第一行