Question

大家好！我是Java的新手，尤其是OOP。我受命编写一个有关篮球和排球队注册的三节课程序。这是一个简单的算法，有一件事我无法理解。我有三个班级，“会员”，“团队”和“测试”（我的主要工作方向）。每当我运行程序时，我都会不断收到NullPointerException。这是我的代码。

团队班级

package MyLibs;

/**
 *
 * @author anonymous
 */
public class Team {

    public String name;
    public Member [] members;
    public int memberCnt;
    public int maxMember;
    public int minAge;
    public int maxAge;

    public Team(String name, int maxMember, int minAge, int maxAge) {
        this.name = name;
        this.maxMember = maxMember;
        this.minAge = minAge;
        this.maxAge = maxAge;
    }

    public void addMember(Member  member){
        members[memberCnt] = member;
        memberCnt++;
    }

    public boolean checkQualification(Member member){

        if (member.age < minAge || member.age > maxAge)
            return false;
        else
            return true;

    }



}

会员等级

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package MyLibs;

/**
 *
 * @author anonymous
 */
public class Member {

    public String name;
    public int age;

    public Member(String name, int age) {
        this.name = name;
        this.age = age;
    }




}

主类

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package MyApp;

import java.util.Scanner;
import MyLibs.*;

/**
 *
 * @author anonymous
 */
public class Test {
    public static void main(String[] args) {
        String bBall_name;
        int bBall_age;
        String vBall_name;
        int vBall_age;
        boolean res;
        int choice;


        Scanner scan = new Scanner(System.in);

        System.out.println("Select Team");
        System.out.println("-----------------");
        System.out.println("[1] Basketball");
        System.out.println("[2] Volleyball");
        System.out.println("[3] Exit");
        System.out.println("-----------------\n");

        do{
        System.out.print("Enter choice: ");

        choice = scan.nextInt();
        scan.skip("\n");

        switch (choice){

            case 1:

                System.out.println("\nYou choose Basketball!\n");
                System.out.print("Name: ");
                bBall_name = scan.nextLine();
                System.out.print("Age: ");
                bBall_age = scan.nextInt();


                Team basketball = new Team(bBall_name, 5, 18, 30);
                Member bBall_mem = new Member(bBall_name, bBall_age);



                if(basketball.memberCnt == basketball.maxMember){
                    System.out.println("\nBasketball team is no longer accepting applicants.\n");
                    break;
                }

                res = basketball.checkQualification(bBall_mem);

                if(res == true){
                    System.out.println("\nWelcome to the Basketball team!\n");
                    basketball.addMember(bBall_mem);
                }else{
                    System.out.println("\nSorry, you are not qualified!\n");
                    break;


                }



                break;
            case 2:


                System.out.println("\nYou choose Volleyball!\n");
                System.out.print("Name: ");
                vBall_name = scan.nextLine();
                System.out.print("Age: ");
                vBall_age = scan.nextInt();


                Team volleyball = new Team(vBall_name, 3, 14, 20);
                Member vBall_mem = new Member(vBall_name,vBall_age);

                if (volleyball.memberCnt == volleyball.maxMember){
                    System.out.println("Volleyball team is no longer accepting applicants.\n");
                    break;
                }

                res = volleyball.checkQualification(vBall_mem);

                if(res == true){
                    System.out.println("\nWelcome to the Volleyball team!\n");
                    volleyball.addMember(vBall_mem);

                }else{
                    System.out.println("\nSorry, you are not qualified!\n");
                    break;
                }

                break;




        }

    }while(choice != 3);


    }

}

错误发生在

basketball.addMember（bBall_mem）;

和

volleyball.addMember（vBall_mem）;

我不知道为什么总是出现该错误。我已经检查过了，我不认为它为空。请放心，这确实是我的第一次。谢谢大家为我提供帮助。

PS>我也是这里的新手：）

Answer 1

您不会在Team类中初始化Member数组。

只需在您的Team类构造函数中添加以下行：

this.members = new Member[maxMember];

或者像其他人建议的那样，您最好为此使用列表而不是数组

从其他类填充数组时，出现Unidentified NullPointerException

1 个答案: