Java：while 循环未检测到中断条件，但 if 块检测到

Question

just want to break out of this while loop. Condition doesn't break when I assumed it will, but it does get registered by the subsequent if statement.

  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.
    }

Possibly some kind of call order problem as the String is "empty" upon entering the while loop. Sorry for any formatting.

Thanks for any and all help.

NOTE: I typically use C# and as far as I remember, a while loop will try and detect the condition case before completing an entire iteration.

EDIT: The if statement is not there to run, but to just prove two things: 1) that the break condition can be detected and 2) to break out at a given time.

EDIT: Updated to show all code in consideration.

Answer 1

Try changing the implementation to:

    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

Your question appears to have been based on a misconception, the while loop will only terminate when the condition is re-evaluated to be false at the top (not on the instant of the variable being updated). However , you can make it so the prompt, the assignment and the evaluation happen at once. First, create a helper method. Like,

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

Then, use it with the fact that assignment (as a side-effect) evaluates to the assigned value; also, please follow standard Java camel case naming conventions. Like,

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'");