所以这是我的Superhero类:

public class Superhero {

  public int strength;
  public int powerUp;
  public int defaultStrength = 10;
  public String name;

  public Superhero(String name) {
     this.strength = 10;
     System.out.println("The Superheroes available are :" + name);
  }

  public Superhero(String name, int strength) {
     if (strength >= 0) {
      this.strength = strength;
      System.out.println("The Superheroes available are :" + name);
     } else {
      System.out.println("Error. Strength cannot be < 0");
     }
  }

  public void setStrength( int strength ) {
     this.strength = strength;
  }

  public int getStrength() {
    return strength;
  }

  public void powerUp(int powerUp) {
    this.strength += powerUp;
  }

}


这是我的Fight类,这里的问题是当我运行它时,我得到的是获胜者的结果是null,我不明白为什么这样做。

import java.io.*;

public class Fight {

  public static void main (String args[]) {

    Superhero gambit = new Superhero( "Gambit" );

    Superhero groot = new Superhero( "Groot", 79);

    System.out.println( "Gambit's strength is: " + gambit.strength);
    System.out.println( "Groot's strength is: " + groot.strength);
    System.out.println("The winner of the fight is: " + fight(gambit, groot));

  }

  static String fight(Superhero a, Superhero b)
  {
    if (a.strength > b.strength)
    {
       return a.name;
    } else
    {
       return b.name;
    }
  }
}

最佳答案

看一下你的构造函数:

public Superhero(String name) {
   this.strength = 10;
   System.out.println("The Superheroes available are :" + name);
}


设置实例字段strength,但对name实例字段不执行任何操作。您的其他构造函数是相同的。您需要包括:

this.name = name;


将值从参数复制到实例变量。在两个构造函数中都执行此操作。否则,您最终只能得到name的默认值,它是空引用。

顺便说一句,我强烈建议您将字段设为私有,并添加getName()方法以从fight方法中检索名称。如果强度低于0,我也将引发异常,而不是仅仅打印出错误消息,而且我将使不采用strength参数的构造函数仅链接到执行该操作的参数:

public Superhero(String name) {
    this(name, 10);
}

public Superhero(String name, int strength) {
    if (strength < 0) {
        throw new IllegalArgumentException("strength cannot be negative");
    }
    this.strength = strength;
    this.name = name;
    System.out.println("The Superheroes available are :" + name);
}


(构造函数显示的消息有点奇怪,因为它只列出一个名称,但这是另一回事。)

关于java - 不明白为什么我会收到null,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/33175627/

10-11 22:28
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