字符串输入在if-else语句中不起作用

Question

我是Java的新手，我创建了某种迷你游戏，我希望玩家选择是否要重新玩，我尝试将start boolean变量更改为静态类型并添加一些代码行，但是该代码似乎不起作用，每次我玩游戏时，它的确询问我是否要重播，但是问题是，即使我最后在控制台上输入“是”，游戏也不会似乎没有重启。 谁能帮我，我将非常感谢，谢谢！

import java.util.Random;
import java.util.Scanner;

//Rocks, papers, scissors game complied by William To.
public class RockPaperScissor {
static int gamePlays = 0;
static boolean start = true;
public static void main(String[] args) {
    while (start){
        @SuppressWarnings("resource")
        Scanner userInput = new Scanner(System.in);
        Random comOutput = new Random();
        System.out.println("Do you choose rock, paper or scissor?");
        String userChoice = userInput.nextLine();
        int comChoice = comOutput.nextInt(2);
        switch (userChoice){

        case "rock":
            if(comChoice == 0){
                System.out.println("I choose rock too! That's a draw!");
            } else if(comChoice == 1){
                System.out.println("I choose paper! I win!");
            } else {
                System.out.println("I choose scissor! You win!");
            }
            break;

        case "paper":
            if(comChoice == 0){
                System.out.println("I choose rock! You win!");
            } else if(comChoice == 1){
                System.out.println("I choose paper too! That's a draw!");
            } else {
                System.out.println("I choose scissor! I win!");
            }
            break;

        case "scissor":
            if(comChoice == 0){
                System.out.println("I choose rock! I win!");
            } else if(comChoice == 1){
                System.out.println("I choose paper! You win!");
            } else {
                System.out.println("I choose scissor too! That's a draw!");
            }
            break;
        default :
            System.out.println("I don't think that's an option.");
            break;
        }
        gamePlays++;
        System.out.println("You've played " + gamePlays + " games.");

               //BELOW IS THE PART I want to ask, what's wrong? 

        System.out.println("Do you want to play again?"); 
        String playAgain = userInput.next();
        if (playAgain == "yes"){
            System.out.println("Restarting game...");
            start = true;
        } else if (playAgain == "no") {
            System.out.println("Quitting game.");
            start = false;
        }
    }
}   
} 

从Eclipse打印出来的内容：

Do you choose rock, paper or scissor?  
rock **//my input**    
I choose paper! I win!  
You've played 1 games.  
Do you want to play again?    
yes **//my input**    
Do you choose rock, paper or scissor?  
paper **//my input**    
I choose paper too! That's a draw!  
You've played 2 games.  
Do you want to play again?  
no **//my input**  
Do you choose rock, paper or scissor? 

Answer 1

字符串之间的比较需要使用String＃equals而不是== 。 所以这：

if (playAgain == "yes"){
    System.out.println("Restarting game...");
    start = true;
} else if (playAgain == "no") {
    System.out.println("Quitting game.");
    start = false;
}

必须成为这样：

if (playAgain.equals("yes")){
    System.out.println("Restarting game...");
    start = true;
} else if (playAgain.equals("no")) {
    System.out.println("Quitting game.");
    start = false;
}

为了工作正常。

但是，我建议使用String＃equalsIgnoreCase ，因为使用equals ，比较区分大小写，因此，如果用户输入Yes或yEs ， playAgain.equals("yes")将返回false

更新

正如Maroun Maroun所说，最好使用

"yes".equals(playAgain)

和

"no".equals(playAgain)

因为如果playAgain为null ，则不会抛出NullPointerException

Answer 2

尝试：

    if ("yes".equals(playAgain)) {
        System.out.println("Restarting game...");
        start = true;
    } else if ("no".equals(playAgain)) {
        System.out.println("Quitting game.");
        start = false;
    }

String＃equals（）检查字符串的字符是否相等， ==检查内存引用。

Answer 3

问题可能是这条线

if (playAgain == "yes")

（以及后来的一个）。

Java中的字符串是对象。 这意味着两个字符串可能具有相同的内容 ，即包含相同的文本，但就==而言，仍然不是“相同”。 要比较两个字符串并查看它们是否包含相同的文本，请使用以下命令：

if (playAgain.equals("yes"))

Answer 4

问题是String比较完成的方式。

playAgain == "yes" ，此检查将检查对象是否相等。

但是，在这种情况下，需要比较对象的值，以下代码将为您工作。

playAgain.equals("yes")

Answer 5

您需要使用String.equals()方法而不是==比较字符串

equals方法比较字符串的值，并且==检查两个对象是否引用相同的对象。