JAVA双输入错误(线程 "main"java.lang.NullPointerException中出现异常)

Question

我的代码中出现Thread "main"java.lang.NullPointerException 异常错误。

这应该是玩家和怪物之间战斗的模拟。每两周我就会接到一项任务，用新功能对其进行升级。这周我必须制作另一个版本的怪物:这里它受到普通攻击的一半伤害和法术伤害的一半。(ChargeMonster.java 是另一个任务，但它有效)

问题出在 ResistantMonster.java 中，但我不知道它是什么，所以我将包含我的整个代码。

Exception in thread "main" java.lang.NullPointerException
at ResistantMonster.takeDamage(ResistantMonster.java:12)
at Character.attack(Character.java:48)
at Game.main(Game.java:161)

代码:

public class ResistantMonster extends Monster {

    public ResistantMonster(int maxHp, int atk, double hitChance) { 
        super(maxHp, atk, hitChance);
    }

    public void takeDamage(int damage) {
        if (input.equals("1")) { // exception occurs here
            currentHp -= ((int) 0.5 * damage);
        } else { 
            currentHp -= ((int) 1.5 * damage);
        if (getCurrentHp() < 0) {
            currentHp = 0;
        }
    }
}

public class Game {

    public static void main(String[] args) {
        Player player = new Player(150, 30, 60, 3, 0.7, 100, 15); 
        Monster[] monsters = new Monster[5];
        for (int i = 0; i < 5; i++) {
            monsters[i] = new ResistantMonster(100 + (int) (Math.random() * 101), 20 + (int) 
        } 
        Monster monster = monsters[(int) (Math.random() * 5)];

        Scanner sc = new Scanner(System.in); 
        String input;

        int turn = 0;

        while (player.getCurrentHp() > 0 && monster.getCurrentHp() > 0) { 
            System.out.println("----------------------------------------------------------------");
            System.out.println("Round " + turn);
            System.out.println(player.toString());
            System.out.println(monster.toString());
            System.out.println("----------------------------------------------------------------");
            System.out.println("Possible commands:");
            System.out.println("1 -> Attack");
            System.out.println("2 -> Item (" + player.getRemainingItemUses() + " remaining)");
            System.out.println("3 -> Fire-Spell (AP 50)");
            System.out.println("4 -> Water-Spell (AP 40)");
            System.out.println("5 -> Thunder-Spell (AP 30)");
            System.out.println("Which command??");          

            input = sc.nextLine();

            if (input.equals("1")) {
                turn++;
                System.out.println("Player attacks!");
                if ( player.attack(monster) != -1) {  //!!!!errorline
                    System.out.println("Player hits!");
                } else {
                    System.out.println("Player missed.");
                } 
            } else if (input.equals("2")) {
                turn++;
                if ( player.heal(player.getHealingPower())) {
                    System.out.println("Player uses a healing potion.");
                } else {
                    System.out.println("Player has no more potions.");
                }
            } else if (input.equals("3")) {
                turn++;
                if (player.spell1(monster)) {
                    System.out.println("Player uses a fire spell!");
                } else {
                    System.out.println("Player has not enough ability points left.");
                } 
            } else if (input.equals("4")) {
                turn++;
                if (player.spell2(monster)) {
                    System.out.println("Player uses a water spell!");
                } else {
                    System.out.println("Player has not enough ability points left.");
                }
            } else if (input.equals("5")) {
                turn++;
                if (player.spell3(monster)) {
                    System.out.println("Player uses a thunder spell!");
                } else {
                    System.out.println("Player has not enough ability points left.");
                }
            } else {
                turn++;
                System.out.println("Invalid Command");
            }
            player.regenerateAp(); 

            if (monster.isDefeated()) {
                break; 
            }

            System.out.println("Monster attacks!");

            int ret = monster.action(player);
            if ( ret >= 0) {
                System.out.println("Monster hits!");
            } else if( ret == -1) { 
                System.out.println("Monster missed.");
            } else {
                System.out.println("Monster charges.");
            }
        }

        sc.close();
        System.out.println("----------------------------------------------------------------");
        System.out.println("Game over in round " + turn);
        System.out.println(player.toString());
        System.out.println(monster.toString());
        System.out.println("----------------------------------------------------------------");

        if (player.isDefeated()) {
            System.out.println("Player won!");
        } else {
            System.out.println("Player lost!");
        }
    }
}

public class Character {
    protected int currentHp; 
    protected int atk;
    protected double hitChance;

    public Character(int maxHp, int atk, double hitChance) {
        this.currentHp = maxHp;
        this.atk = atk;
        this.hitChance = hitChance;
    }

    public void takeDamage(int damage) { 
        currentHp -= damage;
        if (getCurrentHp() < 0) {
            currentHp = 0;
        }
    }

    public boolean isDefeated() {
        if (getCurrentHp() == 0) {
            return true;
        } else {
            return false;
        }
    }

    public int getAtk() { 
        return this.atk;
    }

    public int getCurrentHp() {
        return this.currentHp;
    }

    public int attack(Character target) {
        if (Math.random() <= hitChance) {
            int damage = (int) (atk * (Math.random() + 1.0));
            target.takeDamage(damage); //!!!!errorline
            return damage;
        } else {
            return -1;
        }
    }

    public String toString() {
        return "HP " + currentHp + " - ATK " + atk + " - Hit Chance " + hitChance;
    }
}

public class Monster extends Character {

    public Monster(int maxHp, int atk, double hitChance) { 
        super(maxHp, atk, hitChance);
    }

    public int action(Character target) {
        return attack(target);
    }

    public String toString() {
        return "Monster: HP " + currentHp + " - ATK " + atk + " - Hit Chance " + hitChance;
    }
}

public class ChargeMonster extends Monster {
    private double chargeChance = 0.2; 

    private boolean charged = false;

    public ChargeMonster(int maxHp, int atk, double hitChance) { // Konstruktor
        super(maxHp, atk, hitChance);
    }

    public int action(Character target) {
        if (!charged) { 
            double rdm = Math.random();
            if ( rdm > chargeChance) {
                return attack(target);
            } else {
                charged = true;
                return -2;
            } 
        } else {
           return attack(target);
        }
    }

    public int attack(Character target) {
        if (!charged) {
            if (Math.random() <= hitChance) {
                int damage = (int) (atk * (Math.random() + 1.0));
                target.takeDamage(damage);
                return damage;
            } else {
                return -1;
            }
        } else {
            if (Math.random() <= hitChance) {
                int damage = (int) (atk * (Math.random() + 2.5));
                target.takeDamage(damage);
                charged = false;
                return damage;
            } else {
                return -1;
            }
        }
    }
}

PS:如果需要，我可以复制我的 Player.java

PS2:请对我的编码方式发表评论。任何改进的建议都会非常棒!提前致谢!

Answer 1

根据您的错误，您正在尝试访问空值。您在标记行上访问的唯一内容是输入。因此，您的错误告诉您 input 为空。

您在ResistantMonster类中的什么位置设置input？据我所知，通过查看您的代码，您在任何地方都没有它。

要解决此问题，请通过构造函数或方法takeDamage()。