Java：while循环未检测到中断条件，但如果块确实检测到

Question

只是想打破这个while循环。我认为条件不会破坏条件，但是条件确实会在随后的if语句中注册。

  String current_Class_Name = "";
  int current_Class_Rating;  

    while(!current_Class_Name.equals("Done")) {

      // * Get class name.
      System.out.println("What class are you rating?");
      current_Class_Name = in.nextLine();
      // *
      // if(current_Class_Name.equals("Done")) {
      // System.out.println("Detected 'Done'");
      // break;
      // }

      // * Get class rating.
      System.out.println("How many plus signs does " + current_Class_Name + " get?");
      current_Class_Rating = Integer.parseInt(in.nextLine());

      // * If user inputs an invalid rating (not a value between 0-5),
      // * keep prompting them until they enter a valid input.
      while(current_Class_Rating > 5 || current_Class_Rating < 0) {
        System.out.println("Sorry, but you can only give a rating of 0-5.");
        System.out.println("How many plus signs does " + current_Class_Name + " get?");
        current_Class_Rating = Integer.parseInt(in.nextLine());
      }

      // * TODO
      // * Add to STRING and INTEGER LISTS.
    }

可能某种呼叫顺序问题，因为字符串是“空”在进入while循环。对不起，任何格式。

感谢您提供所有帮助。

注意：我通常使用C＃，据我所记得，while循环将在完成整个迭代之前尝试检测条件情况。

编辑：if语句不是要运行的，而只是证明两件事：1）可以检测到中断条件，以及2）在给定时间爆发。

编辑：已更新为显示正在考虑的所有代码。

Answer 1

尝试将实现更改为：

    String current_Class_Name = null;
    Integer current_Class_Rating = null;

    do {
        // * Get class name.
        System.out.println("What class are you rating?");
        current_Class_Name = in.nextLine().trim();


        try {
            // * Get class rating.
            System.out.println(String.format("How many plus signs does '%s' get?",current_Class_Name));
            current_Class_Rating = Integer.parseInt(in.nextLine().trim());
        }catch(NumberFormatException e) {
            current_Class_Rating = null;
        }

        if((current_Class_Rating == null)||(!(current_Class_Rating>=0 && current_Class_Rating <=5))) {
            System.out.println("Invalid rating value! Rating must be integer 0-5!");
            continue;  // skips back to beginning of the loop
        }

        // * TODO
        // * Add to STRING and INTEGER LISTS.

    }while(!current_Class_Name.equalsIgnoreCase("done"));

Answer 2

您的问题似乎是基于一个错误的观念，while循环只会在条件重新评估为顶部的false时才终止（而不是在更新变量的那一刻）。 但是，您可以完成，因此提示，任务和评估立即发生。首先，创建一个辅助方法。喜欢，

private static String promptForClassName(Scanner in) {
    System.out.println("What class are you rating?");
    return in.nextLine();
}

然后，将其与赋值（作为副作用）求值为赋值的事实一起使用；另外，please遵循标准的Java camel大小写命名约定。喜欢，

String currentClassName;
while (!(currentClassName = promptForClassName(in)).equalsIgnoreCase("Done")) {
    String prompt = "How many plus signs does " + currentClassName + " get?";
    // * Get class rating.
    System.out.println(prompt);
    int currentClassRating = Integer.parseInt(in.nextLine());

    // * If user inputs an invalid rating (not a value between 0-5),
    // * keep prompting them until they enter a valid input.
    while (currentClassRating > 5 || currentClassRating < 0) {
        System.out.println("Sorry, but you can only give a rating of 0-5.");
        System.out.println(prompt);
        currentClassRating = Integer.parseInt(in.nextLine());
    }

    // * TODO
    // * Add to STRING and INTEGER LISTS.
}
System.out.println("Detected 'Done'");