java - 如何解决将数组返回到空数组Java

Question

我一直收到这个错误:

Exception in thread "main" java.lang.NullPointerException at BattleshipCMDGame.GenerateShips(BattleshipCMDGame.java:33) at BattleshipCMDGame.main(BattleshipCMDGame.java:7)

我想要做的就是将我的方法中新创建的类类型数组返回到 main 方法中创建的空数组中。这是我的代码:

import java.util.*;

public class BattleshipCMDGame
{
public static void main(String[] args)
{
    Ship[] ship = GenerateShips(3);
    Scanner in = new Scanner(System.in);

    for (int i = 0; i < ship.length; i++)
    {
        System.out.println(ship[i].GetName() + " : Location - " + ship[i].GetLocation());
    }
}

public static Ship[] GenerateShips(int numShips)
{
    Ship[] ship = new Ship[numShips];
    Random rand = new Random();
    int randLoc;
    String prevRands = "";
    String randToString = "";

    for (int i = 0; i < ship.length; i++)
    {
        randLoc = 1 + rand.nextInt(7);
        randToString = Integer.toString(randLoc);

        for (int z = 0; z < ship.length; z++)
        {
            prevRands = "";

            if (ship[z].GetLocation() != 0)
            {
                prevRands += Integer.toString(ship[z].GetLocation());
            }
        }

        while (prevRands.contains(randToString))
        {
            randLoc = 1 + rand.nextInt(7);
            randToString = Integer.toString(randLoc);
        }

        ship[i] = new Ship("Ship no. " + (Integer.toString(i)), randLoc);
    }

    return ship;
}
}

Answer 1

if (ship[z].GetLocation() != 0)

ship[z] 为空 (null)，所以这就是您收到错误的原因。您需要先填充您的 ship 数组。

重要的是:ship 数组存储引用 而不是对象，所以这就是为什么你需要先填充它。所以

Ship[] ship = new Ship[10]

存储 10 个 Ship 引用(以 null 开头)，您需要自己分配的实际 Ship 对象。