嘗試循環回到開始時陷入無限循環。 Java

Question

我想讓代碼循環，如果用戶輸入無效的大小。但它陷入了無限循環。我試着將「while」帶到底部並添加「do」來啓動循環，但是我得到的結果相同，或者代碼停止循環返回到開頭。

import javax.swing.JOptionPane; 
import java.text.DecimalFormat; 

public class BarkingLotJOP5 
{ 
    public static void main(String[] args) 
    { 
     String size; 
     Double sm = 8.00, md = 12.00, lg = 17.00, total, tax = .09; 
     DecimalFormat df = new DecimalFormat("$###,###.##"); 

      JOptionPane.showMessageDialog(null,"Welcome to BarkingLot.com."); 
      JOptionPane.showMessageDialog(null, "It is $5 for small, $10 for medium, and $15 for large."); 

     size = JOptionPane.showInputDialog("Enter the dog's size."); 

     while 
      (!size.equals("small") || size.equals("medium")|| size.equals("large")) 
       { 
     if 
      (size.equalsIgnoreCase("small")) 
       { 
       total = (sm*tax)+sm; 
       JOptionPane.showMessageDialog(null,"For a small dog, your total is "+ df.format(total)+ 
                     "\nThank you, have a great day!"); 
       } 
     else 
     if 
      (size.equalsIgnoreCase("medium")) 
       { 
       total = (md*tax)+md; 
       JOptionPane.showMessageDialog(null,"For a medium dog, your total is "+ df.format(total)+ 
                       "\nThank you, have a great day!"); 
       } 
     else 
     if 
      (size.equalsIgnoreCase("Large")) 
          { 
          total = (lg*tax)+lg; 
          JOptionPane.showMessageDialog(null,"For a large dog, your total is "+ df.format(total)+ 
                  "\nThank you, have a great day!"); 
        } 
     else 
      JOptionPane.showMessageDialog(null,"Error"); 
       } 
    } 
} 

Answer 1

while(!(size.equals("small") || size.equals("medium")|| size.equals("large"))) 

（注意括號）。基本上你的代碼進行覈對，如：

不斷循環，如果：

大小不等於：small

或

大小等於到：medium

或

尺寸爲等於到：large

但是你想：

不斷循環，如果：

大小不等於（小型或中型或大型）

編輯：

在其他情況下，而不是：

else 
      JOptionPane.showMessageDialog(null,"Error"); 

你可以使用：

else{ 
    JOptionPane.showMessageDialog(null,"Error, try again"); 
    size = JOptionPane.showInputDialog("Enter the dog's size."); 
} 

這將使得輸入框中再次出現，並重新設置大小的值到新值。

Answer 2

break聲明將爲你做的伎倆。

並刪除了!登錄!size.equals("small")

while (size.equals("small") || size.equals("medium") || size.equals("large")) { 
     if (size.equalsIgnoreCase("small")) { 
      total = (sm * tax) + sm; 
      JOptionPane.showMessageDialog(null, "For a small dog, your total is " + df.format(total) 
        + "\nThank you, have a great day!"); 
      break; 
     } else if (size.equalsIgnoreCase("medium")) { 
      total = (md * tax) + md; 
      JOptionPane.showMessageDialog(null, "For a medium dog, your total is " + df.format(total) 
        + "\nThank you, have a great day!"); 
      break; 
     } else if (size.equalsIgnoreCase("Large")) { 
      total = (lg * tax) + lg; 
      JOptionPane.showMessageDialog(null, "For a large dog, your total is " + df.format(total) 
        + "\nThank you, have a great day!"); 
      break; 
     } else { 
      JOptionPane.showMessageDialog(null, "Error"); 
      break; 
     } 
    } 

更新的面前：

，我建議你在這種情況下使用switch代替while。它對我來說看起來更加準確。

switch (size) { 

     case "small": 
      total = (sm * tax) + sm; 
      JOptionPane.showMessageDialog(null, "For a small dog, your total is " + df.format(total) 
        + "\nThank you, have a great day!"); 
      break; 
     case "medium": 
      total = (md * tax) + md; 
      JOptionPane.showMessageDialog(null, "For a medium dog, your total is " + df.format(total) 
        + "\nThank you, have a great day!"); 
      break; 
     case "large": 
      total = (lg * tax) + lg; 
      JOptionPane.showMessageDialog(null, "For a large dog, your total is " + df.format(total) 
        + "\nThank you, have a great day!"); 
      break; 
     default: 
      JOptionPane.showMessageDialog(null, "Error"); 
      break; 

    } 

Answer 3

提示在循環中。

do { size = JOptionPane.showInputDialog("Enter the dog's size.");

等等等等

} 
while (!(size.equals("small") || size.equals("medium") || size.equals("large"))) 

添加括號一段時間。

休息很好