Java中的while循环（二十一点）

Question

I am trying to program a basic game of Blackjack. The problem I am having is I can not get the program to allow input after the first choice within the loop. For example if the player chooses to hit on their first turn, it works, but on their next turn I can not get the program to allow input. here is what i have. any suggestions?

import java.util.Scanner;

public class BlackJack {

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    System.out.println("Welcome to BlackJack");
    int guess = 1+(int)(Math.random()*13);
    int guess2 = 1+(int)(Math.random()*13);
    int answer = guess + guess2;
    System.out.println("Player 1 hand: " + answer);
    System.out.println("Do you want to hit(1) or stay(2)");

    boolean looping = true;
    while(looping){
        int choice = scan.nextInt();
        int guess3 = 1+(int)(Math.random()*13);
        int hand = guess3 + answer;
    if(choice == 1){
        if(guess3 == 1){
            System.out.println("Player 1 drew an Ace!");
            System.out.println("Player 1 hand: " + hand);
            System.out.println("Do you want to hit(1) or stay(2)");
        }else if(guess3 > 1 && guess3 <= 10){
            System.out.println("Player 1 drew a"  + guess3 +"!");
            System.out.println("Player 1 hand: " + hand);
            System.out.println("Do you want to hit(1) or stay(2)");
        }else if(guess3 == 11){
            System.out.println("Player 1 drew a Jack!");
            System.out.println("Player 1 hand: " + hand);
            System.out.println("Do you want to hit(1) or stay(2)");
        }else if(guess3 == 12){
            System.out.println("Player 1 drew a Queen");
            System.out.println("Player 1 hand: " + hand);
            System.out.println("Do you want to hit(1) or stay(2)");
        }else if(guess3 == 13){
            System.out.println("Player 1 drew a King!");
            System.out.println("Player 1 hand: " + hand);
            System.out.println("Do you want to hit(1) or stay(2)");
        }
        if(choice == 2){
            looping = false;
        System.out.println("Player 1 has decided to stay");
        }if(hand > 21){
            looping = false;
            System.out.println("You have busted!");
    }

Answer 1

Your problem is that you are literally taking the user's input only once.

Instead of:

int choice = scan.nextInt();
while(choice == 1){
    // etc.
}

... you should implement an infinite loop:

while (true) {
    int choice = scan.nextInt();
}

... Also, you should catch InputMismatchException s for unexpected input types, and allow the user to get out of the loop.

Altogether I would recommend:

• using the infinite loop as per above
• using Scanner#nextLine instead of Scanner#nextInt
• getting a String as a result
• checking for something starting with "q" or such like for the user wanting to quit
• otherwise, attempting to parse an Integer out of the String with Integer.parseInt and catching the eventually resulting NumberFormatException

Also, I'd strongly recommend using a switch statement to categorize the Integer from the user, instead of the messy if-then-else.

Answer 2

This is because in every if statement you break from the loop and do not enter it again.

What you need is a looping condition which is true until either the player busts or chooses to stay and don't break from the loop in every if statement, instead i think you might want to use continue

boolean looping = true;
while (looping){
    int choice = scan.nextInt();
    //.... edit
    if (choice == 1){
         //Do your card/hand handling code here
    }
    //.... end of edit
    else if(choice == 2 || hand >= 22){
         looping = false;
         continue;  //Alternatively just break;
    }
}

Also you could reduce all your if statements to fewer cases as for 2-10 you could just do this

if(guess3 > 1 && guess3 <= 10){
    System.out.println("Player 1 drew an "  + guess3 +"!");
    System.out.println("Do you want to hit(1) or stay(2)");
}

EDIT In response to your comments.

The program will keep adding cards as all your card handling code needs to be in the following condition

if (choice == 1){
     //Do your card/hand handling code here
}

Currently this is not the case so your program with just add cards every time as you don't check what the user has chosen.

Answer 3

Your use of the break statements means that your loop performs a very limited function, more like an if. On breaking out of the loop you have no more code to run.

If your loop worked your use of answer and hand variables means that you would never get a correct value (each time around the loop just adding the original two values to the third value). Either store the cards in a list, or keep a cumulative score.

You have a lot of repetition, consider using a switch case on guess3 where 1 outputs the Ace statement 2 through 10 are all the same (so, no break statements) 'System.out.println("Player 1 drew a " + guess3 + "!");'. This can be followed by the prompt for stick/twist and the reading of the next value.