试图弄清楚如何将输入键作为用户输入信号 printMenu()

Question

我已经编写了以下应用程序，一切正常。然而，在用户输入对应于菜单命令的值（1-7）后，该命令被执行，然后程序终止。我正在尝试找到一种方法，允许我在显示命令结果后要求用户“按 Enter”，以重新打印菜单并继续输入命令，直到它们准备好退出 (8)。这意味着按下回车将重新打印菜单并允许输入更多命令（1-8）。我知道这需要作为一个循环来完成，但我不确定在这种情况下使用哪个/如何使用循环。谢谢。

import java.util.*;
import java.io.*;

public class RosterApplication {

    Scanner in = null;

    public static void main(String[] args) {
        Roster studentRoster = new Roster();
        studentRoster.loadData("assg3_roster.txt");

        printMenu();

        Scanner keyboard = new Scanner(System.in);
        String entry = keyboard.next();

        if (entry.equals("1")) { //Display the roster
            studentRoster.displayRoster();
        }
        //System.out.println("Press enter to continue:");
        //String reload = keyboard.nextLine();
        //if (reload.equals("")) {
        //  printMenu();
        //}
        if (entry.equals("2")) { //Search for a student by id
            System.out.println("Please enter the student id to search: ");
            String searchId = keyboard.next();
            if ((studentRoster.searchForStudent(searchId)) == null) {
                System.out.println("Student not found!");
            }

        }
        if (entry.equals("3")) { //Add a new student
            System.out.println("Please enter the student id to add: ");
            String addId = keyboard.next();
            if (studentRoster.searchForStudent(addId) != null) {
                System.out.println("Error: This student already exists! Student's info displayed above." + "\n");
            } else {
                System.out.println("Please enter the student name: ");
                String addName = keyboard.next() + " " + keyboard.next();
                System.out.println("Please enter the student standing: ");
                String addStanding = keyboard.next();
                System.out.println("Please enter the student major: ");
                String addMajor = keyboard.next();
                studentRoster.addStudent(addId, addName, addStanding, addMajor);
                System.out.println("The entered information has succesfully been added as a new student." + "\n");
            }

        }
        if (entry.equals("4")) { //Remove a student
            System.out.println("Please enter the student id to remove: ");
            String removeId = keyboard.next();
            studentRoster.removeStudent(removeId);
        }
        if (entry.equals("5")) { //Search for student by major
            System.out.println("Please enter the major to search: ");
            String majorSearch = keyboard.next();
            ArrayList < Student > students = studentRoster.getStudentByMajor(majorSearch);
            if (students.size() != 0) {
                System.out.println("The students with this major are listed above.");
            } else {
                System.out.println("Error: There are no students with this major!");
            }
        }
        if (entry.equals("6")) { //Sort and save to file
            studentRoster.Sort();
            studentRoster.Save();
        }
        if (entry.equals("7")) { //Save to file
            studentRoster.Save();
        }
        if (entry.equals("8")) { //Exit
            studentRoster.Save();
            System.exit(0);
        }
        
        keyboard.close();
    }

    private static void printMenu() {
        System.out.println("1. Display the roster");
        System.out.println("2. Search for a student by id");
        System.out.println("3. Add a new student");
        System.out.println("4. Remove a student");
        System.out.println("5. Search for students by major");
        System.out.println("6. Sort and save to file");
        System.out.println("7. Save to file");
        System.out.println("8. Exit");
    }
}

Answer 1

如 cmets 中所述，在函数周围添加 while-loop 将重复输入循环，直到退出。

public static void main(String[] args) {
    Roster studentRoster = new Roster();
    studentRoster.loadData("assg3_roster.txt");
    Scanner keyboard = new Scanner(System.in);
    
    while (true) {
        printMenu();
        String entry = keyboard.next();

        // all the other if-statements

        if (entry.equals("8")) { //Exit
            studentRoster.Save();
            // System.exit(0);
            // Killing the program is not advised, better just leave the loop and terminate regularly
            break;
        }
    }

    keyboard.close();
}

Answer 2

大约一年前，我一直在寻找可以收听输入、转义、替代等的库。感谢您的问题，我找到了a nice library。

将以下依赖添加到pom.xml（使用maven项目）：

    <dependency>
        <groupId>com.1stleg</groupId>
        <artifactId>jnativehook</artifactId>
        <version>2.1.0</version>
    </dependency>

示例代码：

import org.jnativehook.GlobalScreen;
import org.jnativehook.NativeHookException;
import org.jnativehook.keyboard.NativeKeyEvent;
import org.jnativehook.keyboard.NativeKeyListener;

import java.util.logging.Level;
import java.util.logging.LogManager;
import java.util.logging.Logger;

public class GlobalKeyListenerExample implements NativeKeyListener {
    public void nativeKeyPressed(NativeKeyEvent e) {
        System.out.println("Key Pressed: " + NativeKeyEvent.getKeyText(e.getKeyCode()));

        if (e.getKeyCode() == NativeKeyEvent.VC_ESCAPE) {
            try {
                GlobalScreen.unregisterNativeHook();
            } catch (NativeHookException nativeHookException) {
                nativeHookException.printStackTrace();
            }
        }
    }

    public void nativeKeyReleased(NativeKeyEvent e) {
        System.out.println("Key Released: " + NativeKeyEvent.getKeyText(e.getKeyCode()));
    }

    public void nativeKeyTyped(NativeKeyEvent e) {
        System.out.println("Key Typed: " + e.getKeyText(e.getKeyCode()));
    }

    public static void main(String[] args) {

        // Clear previous logging configurations.
        LogManager.getLogManager().reset();

        // Get the logger for "org.jnativehook" and set the level to off.
        Logger logger = Logger.getLogger(GlobalScreen.class.getPackage().getName());

        logger.setLevel(Level.OFF);
        try {
            GlobalScreen.registerNativeHook();
        }
        catch (NativeHookException ex) {
            System.err.println("There was a problem registering the native hook.");
            System.err.println(ex.getMessage());

            System.exit(1);
        }

        GlobalScreen.addNativeKeyListener(new GlobalKeyListenerExample());
    }
}

使用这个库，你可以获得关于点击进入、空格、转义等的信息。上面的例子是完整的，你可以复制并检查它是如何工作的。 Here 是原始示例。
问你是否有什么不明白的地方；）

附：
这里正在检查单击了哪个键。

if (e.getKeyCode() == NativeKeyEvent.VC_ESCAPE) {
    try {
        GlobalScreen.unregisterNativeHook();
    } catch (NativeHookException nativeHookException) {
        nativeHookException.printStackTrace();
    }
}