Question

我的问题就是这样。我试图将字符串声明为特定大小，我排序和所有内容，但唯一有效的是将字符串放在我使用的主类中的main方法中。这令人沮丧，因为我已经尝试了所有我能想到的东西。当我从另一个类导入元素时，为什么元素变得无效？我在移动类中添加了一个main方法，并将其移动到那里进行尝试，但无济于事。这是第一个程序：

    import java.util.Arrays;
public class movesClass {
    public String[] getMoves() {
        return moves;
    }
    String[] moves;
    public static String[] useMove(String[] moves) {
        moves[0] = "punch";
        moves[1] = "kick";
        moves[2] = "defend";
        moves[3] = "run";
        moves[4] = "inventory";
        moves[5] = "rickroll";
        moves[6] = "heal";
        Arrays.sort(moves);
        return moves;
    }
}
And the body of the main one:

    import java.io.*;
import java.util.*;
public class practiceBattle {
    public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);
        Random rand = new Random();
        inventoryClass quant = new inventoryClass();
        movesClass mov = new movesClass();
        String[] moves = mov.getMoves();

        int hp = 0;
        int playerHp = 200;

        String input = "default";

        int damage = 0;

        int hitDif = 50; //default
        int kickChance1 = 0; //default -- goes into hitChance
        int kickChance = kickChance1 - hitDif; //chance to hit
        int hitChance1 = 0;
        int hitChance = hitChance1 - hitDif;

        int runDif = 50; //default
        int runChance1 = 0; //default -- goes into runChance
        int runChance = runChance1 - runDif; //chance to run

        int enemyMinAttack = 0;
        int enemyAttack = 0;

        int index = 0;

        int[] levelArray = {1, 2, 3};
        String[] monsterArray = {"GNOLL", "TROLL", "DRAGON"};
        String monster = monsterArray[rand.nextInt(monsterArray.length)];
        int level = rand.nextInt(levelArray.length) + 1;
        if(level == 1)
        {
            System.out.println("YOUR OPPONENT IS A BABY " + monster + "!");
        }
        else
        {
            System.out.println("YOUR OPPONENT IS A LEVEL " + level + " " + monster + "!");
        }
        if(level == 1)
        {
            hp = rand.nextInt(20) + 41;
            enemyAttack = rand.nextInt(5) + 1;
        }
        else if(level == 2)
        {
            hp = rand.nextInt(20) + 91;
            enemyAttack = rand.nextInt(6) + 5;
        }
        else if(level == 3)
        {
            hp = rand.nextInt(20) + 141;
            enemyAttack = rand.nextInt(7) + 10;
        }
        enemyMinAttack = rand.nextInt(enemyAttack) + 1;

        System.out.println("YOUR OPPONENT'S HP IS: " + hp + "\n");
        int permEnemyAttack = enemyAttack;
        int permEnemyMinAttack = enemyMinAttack;







    ext:
        while(hp > 0)
        {
            enemyAttack = permEnemyAttack;
            enemyMinAttack = permEnemyMinAttack;

            do
            {
                if(playerHp == 0)
                {
                    System.out.println("YOU HAVE DIED. GAME OVER!\n\n\n");
                    break ext;
                }
                else
                {
                    System.out.println("Choose an action:\nkick\npunch\nrun\ndefend\n");
                    input = scan.nextLine();


                    index = Arrays.binarySearch(moves, input);
                    System.out.println(index);
                    if(index < 0)
                    {
                        System.out.println("\n\n\nINVALID INPUT -- TRY AGAIN\n\n\n");
                    }
                }

            } while(index < 0);

这就是我对主要问题的看法，直到问题结束的地方和开始的地方。任何inpu将不胜感激。谢谢！

Answer 1

您永远不会初始化moves内的movesClass字段。它为null，是引用字段的默认值。如果你想初始化它，你必须这样做：

String[] moves = new String[7];

但即使你这样做，数组的元素仍然是null，你必须把实际的字符串放在数组中。看来你的useMoves()是为此而制作的，但它永远不会被调用。无论如何，这种方法有点奇怪。你有一个数组作为参数，你用移动填充然后对它进行排序，但是你返回相同的数组，你已经得到了参数。将Java从一个方法传递给另一个方法或从方法返回时，Java不会复制数组，因此您可以修改作为参数获取的数组。如果您总是希望使用相同的移动初始化moves字段，那么最好在类的构造函数中执行此操作。静态方法无法访问类的实例字段。

空指针异常从另一个类调用String []

1 个答案: