Java 从方法返回 null 值

huangapple
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英文:

Java returning null value from method

问题

ELF 1 [ STATUS: 活着的精灵 ] [ CLAN: 森林 | BEST FRIEND: null ] [ STR: 5 | DEX: 7 | ARM: 1 | MOX: 16 ] [ COINS: 77 | HEALTH: 80 ]

ELF 2 [ STATUS: 活着的精灵 ] [ CLAN: 城市 | BEST FRIEND: HOBBIT 1 ] [ STR: 14 | DEX: 20 | ARM: 18 | MOX: 12 ] [ COINS: 1000 | HEALTH: 80 ]

主类部分：

  1.         // HOBBIT 1 和 2
  2. 		System.out.println("\n让我们创建两个新的霍比特人！");
  3. 		System.out.println("正在创建两个新的霍比特人...");
  4. 		System.out.println("\n霍比特人 1 的名字：");
  5. 		String hobbitName = sc.nextLine();
  6. 		Hobbit hobbit1 = new Hobbit(hobbitName);
  8. 		System.out.println("霍比特人 2 的名字：");
  9. 		String hobbitName2 = sc.nextLine();
  10. 		Hobbit hobbit2 = new Hobbit(hobbitName2, 8, 12, 2, 14, 10, 30);
  11. 		System.out.println("\n" + hobbit1);
  12. 		System.out.println(hobbit2);
  14. 		// ELF 1 和 2
  15. 		System.out.println("\n让我们创建两个新的精灵！");
  16. 		System.out.println("正在创建两个新的精灵...");
  17. 		System.out.println("\n精灵 1 的名字：");
  18. 		String elfName1 = sc.nextLine();
  19. 		Elf elf1 = new Elf(elfName1);
  21. 		System.out.println("精灵 2 的名字：");
  22. 		String elfName2 = sc.nextLine();
  23. 		Elf elf2 = new Elf(elfName2, 14, 20, 18, 12, 1000, 80, "森林", hobbit1);
  24. 		System.out.println("\n" + elf1);
  25. 		System.out.println(elf2);

精灵类代码部分：

  1. import java.util.Random;
  3. public class Elf extends Humanoid {
  5.     private final String clan;    
  6.     private String bestFriend;   
  8.     public Elf(String name) {
  9.         super(name);
  11.         // 随机设置氏族
  12.         Random random = new Random();
  13.         if(random.nextBoolean()){
  14.             clan = "森林";
  15.         } else {
  16.             clan = "城市";
  17.         }
  18.     }
  20.     public Elf(String name, String clan, Hobbit bestFriend) {
  21.         super(name);
  22.         this.clan = clan;
  23.         this.bestFriend = bestFriend.getName();
  24.     }
  26.     public Elf(String name, int strength, int dexterity, int armour, int moxie, int coins, int healthRating, String clan, Hobbit bestFriend) {
  27.         super(name, strength, dexterity, armour, moxie, coins, healthRating);
  28.         this.clan = clan;
  29.         this.bestFriend = bestFriend.getName();
  30.     }
  32.     public String getBestFriend() {
  33.         return this.bestFriend;
  34.     }
  36.     public void setBestFriend(Hobbit bestFriend) {
  37.         this.bestFriend = bestFriend.getName();
  38.     }
  40.     public String getClan() {
  41.         return clan;
  42.     }
  43.     
  44.     // 仅适用于精灵 2 的行
  45.     @Override
  46.     public String toString() {
  47.         return getName() +
  48.                 " [ STATUS: " + super.isAlive() +
  49.                 " 精灵 ] [ CLAN: " + clan +
  50.                 " | BEST FRIEND: " + getBestFriend() +
  51.                 " ]" + super.toString();
  52.     }
  53. }
英文:

I keep having a object come up as null for Elf 1 which is supposed to show BEST FRIEND: HOBBIT 2 but it only shows null. I tried to look for solutions but nothing helped me. Would anyone please help me figure out a solution? Thank you.

example output:

ELF 1 [ STATUS: Alive Elf ] [ CLAN: Forest | BEST FRIEND: null ] [ STR: 5 | DEX: 7 | ARM: 1 | MOX: 16 ] [ COINS: 77 | HEALTH: 80 ]

ELF 2 [ STATUS: Alive Elf ] [ CLAN: City | BEST FRIEND: HOBBIT 1 ] [ STR: 14 | DEX: 20 | ARM: 18 | MOX: 12 ] [ COINS: 1000 | HEALTH: 80 ]

main class

  1.         // HOBBIT 1 AND 2
  2. 		System.out.println("\nLet's create new two Hobbits!");
  3. 		System.out.println("Building two new hobbits...");
  4. 		System.out.println("\nHobbit 1 name: ");
  5. 		String hobbitName = sc.nextLine();
  6. 		Hobbit hobbit1 = new Hobbit(hobbitName);
  8. 		System.out.println("Hobbit 2 name: ");
  9. 		String hobbitName2 = sc.nextLine();
  10. 		Hobbit hobbit2 = new Hobbit(hobbitName2, 8, 12, 2, 14, 10, 30);
  11. 		System.out.println("\n" + hobbit1);
  12. 		System.out.println(hobbit2);
  14. 		// ELF 1 AND 2
  15. 		System.out.println("\nLet's create new two Elves!");
  16. 		System.out.println("Building two new Elves...");
  17. 		System.out.println("\nElf 1 name: ");
  18. 		String elfName1 = sc.nextLine();
  19. 		Elf elf1 = new Elf(elfName1);
  21. 		System.out.println("Elf 2 name: ");
  22. 		String elfName2 = sc.nextLine();
  23. 		Elf elf2 = new Elf(elfName2, 14, 20, 18, 12, 1000, 80, "Forest", hobbit1);
  24. 		System.out.println("\n" + elf1);
  25. 		System.out.println(elf2);

code in elf class

  2. public class Elf extends Humanoid {
  4.     private final String clan;    
  5.     private String bestFriend;   
  7.     public Elf(String name) {
  8.         super(name);
  10.         // randomly sets clan
  11.         Random random = new Random();
  12.         if(random.nextBoolean()){
  13.             clan = "Forest";
  14.         } else {
  15.             clan = "City";
  16.         }
  17.     }
  19.     public Elf(String name, String clan, Hobbit bestFriend) {
  20.         super(name);
  21.         this.clan = clan;
  22.         this.bestFriend = bestFriend.getName();
  23.     }
  25.     public Elf(String name, int strength, int dexterity, int armour, int moxie, int coins, int healthRating, String clan, Hobbit bestFriend) {
  26.         super(name, strength, dexterity, armour, moxie, coins, healthRating);
  27.         this.clan = clan;
  28.         this.bestFriend = bestFriend.getName();
  29.     }
  31.     public String getBestFriend() {
  32.         return this.bestFriend;
  33.     }
  35.     public void setBestFriend(Hobbit bestFriend) {
  36.         this.bestFriend = bestFriend.getName();
  37.     }
  39.     public String getClan() {
  40.         return clan;
  41.     }
  42.     // only for elf 2 line
  43.     @Override
  44.     public String toString() {
  45.         return getName() +
  46.                 " [ STATUS: " + super.isAlive() +
  47.                 " Elf ] [ CLAN: " + clan +
  48.                 " | BEST FRIEND: " + getBestFriend() +
  49.                 " ]" + super.toString();
  50.     }
  51. }```
  53. </details>
  56. # 答案1
  57. **得分**: 2
  59. 你正在调用构造函数 `Elf(String)` 来创建 elf1；这个构造函数设置了族群和名字，仅此而已。没有任何东西会设置“最好的朋友”，所以它保持为空。
  61. <details>
  62. <summary>英文:</summary>
  64. You’re calling the constructor `Elf(String)` to create elf1; this constructor sets the clan and the name and that’s all. Nothing ever sets the “best friend” so it remains null.
  67. </details>

huangapple
  • 本文由 发表于 2020年7月27日 10:05:44
  • 转载请务必保留本文链接：https://java.coder-hub.com/63107730.html
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