Question

希望这是一个快速的问题。我正在制作一个简单的石头剪刀游戏。我做一个随机的计算机选择，并得到用户的选择。但是当我试图找到谁获胜时，如果用于无效输入的块，它会在我的其他地方打印最后一个。

在做出正确选择后，它会打印“输入有效选项”。

import java.util.Random;
import javax.swing.JOptionPane;

public class JavaApplication4 {

    public static void main(String[] args) 
    {
        Random ranNums = new Random();

        int comp = ranNums.nextInt(3);
        String comp2;
        String winner;

        String user = JOptionPane.showInputDialog
                (null, "Enter rock, paper, or scissors");
        user.toLowerCase();

        if(comp == 0)
            comp2 = "rock";
        else if(comp == 1)
            comp2 = "paper";
        else 
            comp2 = "scissors";

        //Computer wins
        if(comp2 == "rock" && user == "scissors")
            winner = "The computer wins";

        else if(comp2 == "paper" && user == "rock")
            winner = "The computer wins";    

        else if(comp2 == "scissors" && user == "paper")
            winner = "The computer wins";

        //Tie game
        else if(comp2 == "rock" && user == "rock")
            winner = "It's a tie";

        else if(comp2 == "paper" && user == "paper")
            winner = "It's a tie";

        else if(comp2 == "scissors" && user == "scissors")
            winner = "It's a tie";

        //User wins
        else if(comp2 == "scissors" && user == "rock")
            winner = "You win!";

        else if(comp2 == "rock" && user == "paper")
            winner = "You win!";

        else if(comp2 == "paper" && user == "scissors")
            winner = "You win!";
        else
            winner = "Enter a valid choice";

        JOptionPane.showMessageDialog(null, "You picked " + user + "\n" +
            "The computer picked " + comp2 + "\n" +
                winner);



    }
}

Answer 1

你不能使用

comp == "paper"

比较java中的字符串。你用

comp.equals("paper")

或如果情况无关

comp.equalsIgnoreCase("paper")

Answer 2

不要使用==来比较字符串。请改用equals或equalsIgnoreCase（...）方法。理解==检查两个对象是否相同，而不是您感兴趣的。另一方面，这些方法检查两个字符串是否具有相同顺序的相同字符，这才是最重要的。而不是

if (fu == "bar") {
  // do something
}

做，

if ("bar".equals(fu)) {
  // do something
}

，或者

if ("bar".equalsIgnoreCase(fu)) {
  // do something
}

简化代码的一种方法是创建一个RockPaperScissors枚举并在比较方法上给它。类似的东西：

enum RockPaperScissors {
   ROCK("Rock"), PAPER("Paper"), SCISSORS("Scissors");

   private String text;
   private static int[][] winMatrix = {{0, -1, 1}, {1, 0, -1}, {-1, 1, 0}};

   private RockPaperScissors(String text) {
      this.text = text;
   }

   @Override
   public String toString() {
      return text;
   }

   // can't use compareTo since it is a final method for enums
   public int compareVs(RockPaperScissors other) {
      int thisOrdinal = ordinal();
      int otherOrdinal = other.ordinal();
      return winMatrix[thisOrdinal][otherOrdinal];
   }
}

然后比较一个枚举与另一个枚举，只需调用其compareVs（...）方法传入另一个枚举。

所以你的巨大if / else块会降低到：

// assuming that user and comp are RockPaperScissors variables
int result = user.compareVs(comp);
if (result == 1) {
   System.out.println("You've won!");
} else if (result == 0) {
   System.out.println("It's a tie!");
} if (result == -1) {
   System.out.println("You've lost!");
}

Answer 3

如果你像我一样，你喜欢原始代码：

import java.util.Random; 
import javax.swing.JOptionPane;

public class JavaApplication4 {

public static void main(String[] args) 
{
    Random ranNums = new Random();

    int comp = ranNums.nextInt(3);
    String comp2;
    String winner;

    String user = JOptionPane.showInputDialog
            (null, "Enter rock, paper, or scissors");
    user.toLowerCase();

    if(comp == 0)
        comp2 = "rock";
    else if(comp == 1)
        comp2 = "paper";
    else 
        comp2 = "scissors";

    //Computer wins
    if(comp2.equals("rock") && user.equals( "scissors"))
        winner = "The computer wins";

    else if(comp2.equals("paper") && user.equals( "rock"))
        winner = "The computer wins";    

    else if(comp2.equals("scissors") && user.equals( "paper"))
        winner = "The computer wins";

    //Tie game
    else if(comp2.equals("rock") && user.equals( "rock"))
        winner = "It's a tie";

    else if(comp2.equals("paper") && user.equals( "paper"))
        winner = "It's a tie";

    else if(comp2.equals("scissors") && user.equals( "scissors"))
        winner = "It's a tie";

    //User wins
    else if(comp2.equals("scissors") && user.equals( "rock"))
        winner = "You win!";

    else if(comp2.equals("rock") && user.equals( "paper"))
        winner = "You win!";

    else if(comp2.equals("paper") && user.equals( "scissors"))
        winner = "You win!";
    else
        winner = "Enter a valid choice";

    JOptionPane.showMessageDialog(null, "You picked " + user + "\n" +
        "The computer picked " + comp2 + "\n" +
            winner);
}
}

希望有所帮助！

Answer 4

您无法比较这样的字符串：if (comp2 == "rock")

您需要写：if ("rock".equals(comp2))

Java Else如果块无法正常工作

4 个答案: