使用布尔值从用户字符串 java 输入验证

Question

I am creating a rock paper scissors game and the only part that I'm hung up on is the input validation. I have tried do/while loops, try/catch but just can't seem to get it to function properly. Below is what I currently have for the getUserChoice method. Any help would be greatly appreciated. Thanks!

public String getUserChoice(){
    String user = " ";
    boolean error = false;

    Scanner in = new Scanner(System.in);
    System.out.println("Please enter rock, paper, or scissors: ");
    user = in.nextLine(); //reads user input

    do {
        if (user.equalsIgnoreCase("rock")) {
            user = "rock";
            error = false;
        }
        else if (user.equalsIgnoreCase("paper")) {
            user = "paper";
            error = false;
        }
        else if (user.equalsIgnoreCase("scissors")) {
            user = "scissors";
            error = false;
        }
    }
    while(error); {
        System.out.println("Please enter valid input: ");
    }
    return user;
}

Answer 1

I guess you want input only "rock" , "paper" and "scissors"

the do just the

if(!input.equals("rock") || !input.equals("paper") || 
            !input.equals("scissors")) System.out.println("invalid input");

or
if(!input.matches("rock|paper|scissors")) System.out.println("invalid input");

Answer 2

You can slightly change your code to:

public String getUserChoice(){
String user = " ";
boolean error = true;

Scanner in = new Scanner(System.in);
System.out.println("Please enter rock, paper, or scissors: ");
user = in.nextLine(); //reads user input

do {
    if (user.equalsIgnoreCase("rock")) {
        user = "rock";
        error = false;
    }
    else if (user.equalsIgnoreCase("paper")) {
        user = "paper";
        error = false;
    }
    else if (user.equalsIgnoreCase("scissors")) {
        user = "scissors";
        error = false;
    } else {
        System.out.println("Please enter valid input: ");
        user = in.nextLine(); 
    }
}
while(error);

return user;
}

boolean error = true; makes the while block to iterate indefinitely, otherwise, It will jump out on the first iteration.

The else block is what gets executed when not a good condition is input. The system.out outside the while just get executed after the loop finishes

A more efficient or readable way to implement this would be to substitute the do-while block by:

while (true){
    if (user.equalsIgnoreCase("rock") || user.equalsIgnoreCase("paper")  || user.equalsIgnoreCase("scissors")){
        return user;
    } else {
        System.out.println("Please enter valid input: ");
        user = in.nextLine(); 
    }       
}