While＆for循环和JOptionPane数据输入连接到for循环

Question

After reading everything in my books that I thought was relevant and none of it helped I'm writing here. I'm a complete novice in Java and I have to solve the following problem: I have to make a DialogProgram based on Tennis. The program has to ask the user "who got the point" and the user has to type in "A" or "B" and that has to be executed until the game is won by either A or B. In the code I have put my questions as notes. I hope that way they will make the most sense.

import java.awt.Color;
import acm.program.*;
import acm.graphics.*;
import javax.swing.JOptionPane;

public class A3 extends DialogProgram
{
  public void run ()
  { 
    JOptionPane.showMessageDialog(null, "Playing: Who got the point?");

    int A = 0;
    int B = 0; 
    int C = 0;

    /*
     * How do I make a loop to execute the JOptionPane until the if or else statement
     * in the for loop is achieved?
     * I think it should be with a while loop but how do I tell it to ask for input 
     * until the for loop is achieved? 
     */
    while ()
    {
      /*
       * I need the JOptionPane to take in only A or B as an answer each time it pops out.
       * How do I tell the JOptionPane to do that?
       * How to connect the input of A or B in the JOptionPane to the for loop so that it
       * counts the times A is inputed and the times B is inputed
       */
      String input = JOptionPane.showInputDialog("Enter A or B");

      for (C = 0; A >= 4 && B <= A-2; B++) 
      {
        if (A >= 4 && B <= A-2)
        {
          // In this case A wins
          JOptionPane.showMessageDialog(null,"Player A Wins!");
        }
        else if (B >= 4 && A <= B-2)
        {
          // In this case B wins
          JOptionPane.showMessageDialog(null,"Player B wins!");
        }
      }
    }
  }
}

Answer 1

First off, some general Java things (I completely understand that you're just learning):

• "Notes" are called "comments"
• variables (like A, B, and C) should start with a lowercase letter (like a, b, and c).

As for your questions, I don't exactly understand what int C is doing. For your while loop, I would put two conditions in it. Check if a == desiredScore and check if b == desiredScore . desiredScore should probably be its own variable and looks like 4 currently. After getting input (stored in your input String), you should do a couple checks on it. String has a bunch of member functions that you will find very useful. Especially check out .equalsIgnoreCase . If the input doesn't match what you want, print a message saying so and don't update any variables (the loop will just continue).

After the loop exits, I would check if a == desiredScore and print a message accordingly. And then check if b == desiredScore and print a message accordindly.

Answer 2

Basically what supersam654 said with some additions. You'll actually have to increase your integer variables, when the user picks either player, Java doesn't magically keep score for you. Also, your for loop makes no sense, since in it B always get a point.

Here's an example:

public void run(int minimumScoreToWin) {
  int a = 0;
  int b = 0;

  JOptionPane.showMessageDialog(null, "Playing a set of tennis.");

  while (true) { // This loop never ends on its own.
    JOptionPane.showMessageDialog(null, "Score is A: " + a + ", B: " + b +
                                        ". Who got the next point?");
    String input = JOptionPane.showInputDialog("Enter A or B");

    if (input.equalsIgnoreCase("A") {
      a++;
    } else if (input.equalsIgnoreCase("B") {
      b++;
    } else {
      JOptionPane.showMessageDialog(null, "Cannot compute, answer A or B.");
      continue; // Skip to next iteration of loop.
    }

    if (a >= minimumScoreToWin && b <= a-2) {
      JOptionPane.showMessageDialog(null,"Player A Wins!");
      break; // End loop.
    } else if (b >= minimumScoreToWin && a <= b-2) {
      JOptionPane.showMessageDialog(null,"Player B Wins!");
      break; // End loop.
    }
  }
}