主菜单选择退出后程序无法终止，求Java代码问题排查

Hey there, let's dig into why your quit option (choice 5) isn't exiting the program as expected!

The Core Issue #

Look at your main method: when you call main_menu(menu_option), you’re running the method to get user input—but you never save the returned menu choice back into the menu_option variable.

Since menu_option starts at 0 and never gets updated, the check if (menu_option == 5) will never be true. That’s why the program skips the exit logic entirely!

Quick Fix #

Update your main method to assign the return value of main_menu to menu_option:

public static void main(String[] args) {
    int menu_option = 0;
    int num_values;
    int unsorted_array[] = null;
    // Assign the returned choice to menu_option here!
    menu_option = main_menu(menu_option);
    if (menu_option == 5) {
        in.close();
        return;
    }
    user_array(unsorted_array);
}

Optional (But Cleaner) Refactor #

Your main_menu method accepts a parameter a but immediately overwrites it—this parameter is unnecessary. You can simplify the method to be parameterless for better readability:

public static int main_menu() {
    System.out.println(" ###### ##### ");
    System.out.println(" # # ## ##### ## # # #### ##### ##### # # # #### ");
    System.out.println(" # # # # # # # # # # # # # # ## # # # ");
    System.out.println(" # # # # # # # ##### # # # # # # # # # # ");
    System.out.println(" # # ###### # ###### # # # ##### # # # # # # ### ");
    System.out.println(" # # # # # # # # # # # # # # # # ## # # ");
    System.out.println(" ###### # # # # # ##### #### # # # # # # #### \n");
    System.out.println("Main Menu\n");
    System.out.println("Select the Sorting method you would like to use. ");
    System.out.println("(1) Bubble sort (Recommended for somewhat sorted data)");
    System.out.println("(2) Selection sort (Recommended for VERY unsorted data)");
    System.out.println("(3) Insertion sort (Recommened when data is nearly sorted)");
    System.out.println("(4) Turtle sort (Recommened for long arrays)");
    System.out.println("(5) Quit");
    
    int userChoice = 0;
    while(true) {
        try {
            userChoice = in.nextInt();
            break;
        } catch(Exception e) {
            System.out.println("Invalid Input, please try again.");
            in.next(); // Clear the invalid input from the scanner
        }
    }
    return userChoice;
}

Then call it in main like this:

menu_option = main_menu();

Quick Note #

Make sure in is a properly initialized Scanner instance (either as a class-level variable or initialized inside main/main_menu)—otherwise you’ll run into compilation errors. You’re already closing the scanner on exit, which is good practice!

内容的提问来源于stack exchange，提问作者Ashwin Kumar