如何使用“stop”作為關鍵字來停止for循環？

Question

我想將“numberOfItems”設置為一個大數字，但想要中途停止循環。 我需要幫助的部分時間。 請不要ArrayList，我還不熟悉。

do
 {
    for(int i=0; i<=numberOfItems; i++)
    {
       System.out.println("Enter product name");
       productName[i]=input.nextLine();
       System.out.println("Enter price of product");
       productPrice[i]=input.nextDouble();
       System.out.printf("%s,%n,%.2f",productName[i],productPrice[i]);
    }
 }
 while (! (productName[i]= input.nextLine("stop")));

Answer 1

你可以在for循環中放入一個if語句來決定何時停止它; 停止循環的指令是break 。

請注意，這意味着您不需要封閉的do循環。

Answer 2

看看你的代碼是如何工作的，最明智的地方就是在輸入產品名稱之后。 這意味着您無法存儲STOP產品......我將其保留為大寫（如果您不關心大小寫，可以使用equalsIgnoreCase ）。

像這樣的東西：

    for(int i=0; i<=numberOfItems; i++)
    {
       System.out.println("Enter product name (or STOP to stop)");
       String tmpProduct = input.nextLine();

       //trim to avoid whitespace
       if ("STOP".equals(tmpProduct.trim())) {
          break; //we stop the loop here
       }

       //they didn't type STOP, guess they wanted a product.
       productName[i]=tmpProduct;


       System.out.println("Enter price of product");
       productPrice[i]=input.nextDouble();
       System.out.printf("%s,%n,%.2f",productName[i],productPrice[i]);
    }

這也避免了對外環的需要。 如果您更願意在每件產品之后詢問（這可能會在一段時間后變得煩人），那么您可以在請求雙倍后進行檢查和提示。

    for(int i=0; i<=numberOfItems; i++)
    {
       System.out.println("Enter product name");

       //they didn't type STOP, guess they wanted a product.
       productName[i]=input.nextLine();

       System.out.println("Enter price of product");
       productPrice[i]=input.nextDouble();
       System.out.printf("%s,%n,%.2f",productName[i],productPrice[i]);

       System.out.println("type STOP to stop or anything else to continue");
       String tmp = input.nextLine();
       //trim to avoid whitespace problems
       if ("STOP".equals(tmp.trim())) {
          break; //we stop the loop here
       }
    }

Answer 3

更新這是增強的答案，詳細解釋

// this method to validate the input after reading the entire line
static public Object interpretedInput(String line){
   if(line.replace(" ", "").equalsIgnoreCase("stop")){ // if stop detected 
      return null; 
   }
   else {// if it's not stop
       for(char c : line.toCharArray()){ // read every char in the line
           if(!Character.isDigit(c) && c!='.'){ // if any non digit is detected that means it should be considered as a string 
              //(note if you want the product name to consist of digits only -> this won't work)
              return line; // return line
          }
      }
   }
   try{return Double.valueOf(line);} // else try to parse the line to extract the double value and return it
   catch(NumberFormatException e){return null;}
}


Scanner input = new Scanner(System.in);
int numberOfItems = 10; // for example
String[]productName = new String[10];
double[] productPrice = new double[10];
for(int i=0; i<numberOfItems; i++){
    System.out.println("Enter product name");
    Object theInput = interpretedInput(input.nextLine()); // the method will return either null or string or double 
    if(theInput==null){ // if it's null that means to stop
         break;
    }
    else if (theInput instanceof String){ // if it's instance of string accept it 
            productName[i]=(String)theInput;
    }
    while(!(theInput instanceof Double)){ // this will repeat until a valid double input is entered 
         //then it will assign it and display the content
         System.out.println("Enter price of product");
         theInput = interpretedInput(input.nextLine());
         if(theInput==null){
              i=numberOfItems; // to terminate the parent for loop as well
                break;
         }
         else if (theInput instanceof Double){
             productPrice[i]=(Double)theInput;
             System.out.printf("%s, %.2f\n",productName[i],productPrice[i]);
         }
         else{System.out.println("Invalid Price");}
    }
}