如何使用Scanner java重复读取用户输入

我正在尝试为我的程序创建一个简单的菜单来读取用户输入。代码如下：

public void menu() {
        String command;

        System.out.println("To operate with words write: a");
        System.out.println("To operate with products write: b");

        System.out.print("\nGive the command: ");
        Scanner scanner = new Scanner(System.in);
        command = scanner.nextLine();

        if (command.equals("a")) {
            System.out.println("\nGood job! You have chosen the word program\n");
            System.out.println("You can only use the following commands: ");
            System.out.println("exit - to exit the program");
            System.out.println("add - to add a word into the map");
            System.out.println("lookup - to lookup a word into the map\n");
            System.out.print("Give a command: ");
            command = scanner.next();
            while(scanner.hasNext()){
                command = scanner.next();
                if(command.equals("add")){
                    this.addWord();
                }

                System.out.print("Give a command: ");
                command = scanner.next(); //Here I get the ERROR that throws Exception
            }
        }

        scanner.close();
    }

public static void main(String [] args)
{
     HashTableInterface table = new HashTable(); 
     Dictionary d = new Dictionary(table); 
     RepositoryInterface repo = new Repository(d); 
     ControllerInterface controller = new Controller(repo); 
     Console c = new Console(controller); 
     c.menu()
}

下面是一个测试，我得到的一个例外：

To operate with words write: a
To operate with products write: b

Give the command: a

Good job! You have chosen the word program

You can only use the following commands: 
exit - to exit the program
add - to add a word into the map
lookup - to lookup a word into the map

Give a command: add
add
Give the word: mar
Give the word's plural: mere
The hash code for mar is: 3
Give a command: Exception in thread "main" java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Scanner.java:907)
    at java.util.Scanner.next(Scanner.java:1416)
    at console.Console.menu(Console.java:56)
    at test.Prog.main(Prog.java:26)

我从while循环中删除了第二个命令=scanner.next（），但它只允许我读取用户输入一次。如何解决这个问题

更新：AddWord方法：

public void addWord() {

        Scanner scanner = new Scanner(new InputStreamReader(System.in));

        System.out.print("Give the word: ");
        String word = scanner.nextLine();
        System.out.print("Give the word's plural: ");
        String plural = scanner.nextLine();
        scanner.close();

        controller.addTheWord(word, plural);
    }

---

您应该在

while

循环中使用

开关盒，而不是
if
。开关盒应根据用户提供的输入提供功能
 您可以使用

InputStreamReader str= new InputStreamReader (System.in);
BufferedReader uinp= new BufferedReader (str);
String val;
val= uinp.readLine();
while (!".".equals(val)) {
//do your stuff
//..and after done, read the next line of the user input.
val= uinp.readLine();
}

为什么不这样做：

public class test {

private static Scanner scanner;

public static void main(String args[]) {
    scanner = new Scanner(System.in);
    printmenu();      
    getinput();
}

private static void printmenu(){
    System.out.println("To operate with words write: a");
    System.out.println("To operate with products write: b");
}

private static void getinput(){
    System.out.print("\nGive the command: ");
    String command = "";
    while (!scanner.hasNext()) {

    }
    command = scanner.next();

    if (command.equals("a")) {
        System.out.println("\nGood job! You have chosen the word program\n");
        System.out.println("You can only use the following commands: ");
        System.out.println("exit - to exit the program");
        System.out.println("add - to add a word into the map");
        System.out.println("lookup - to lookup a word into the map\n");
        System.out.print("Give a command: ");

        while(scanner.hasNext()){
            command = scanner.next();
            if(command.contains("add")){

                addWord();
            }
            else{
                System.out.println(command);
            }
            getinput();
        }
    }
    else{
        scanner.close();
    }
}

public static void addWord() {

    System.out.print("Give the word: ");
    String word = scanner.next();
    System.out.print("Give the word's plural: ");
    String plural = scanner.next();
    //controller.addTheWord(word, plural);
}

}
请显示您的主界面。@AliAlamiri这是我的主界面：HashTableInterface table=new HashTable（）；字典d=新字典（表）；RepositoryInterface repo=新存储库（d）；控制器接口控制器=新控制器（回购）；控制台c=新控制台（控制器）；c.菜单（）；你能发布你的addWord（）方法吗？是使用nextLine（）读取用户输入吗？@CodingBird使用该方法更新了帖子您是从文本文件获取用户输入吗？引发NoTouchElementException的一个可能原因是，您试图读取已到达数据末尾的输入，直到并且除非您给出“.”，否则它会继续请求用户输入。@实际上，我们看不到您的屏幕。请告诉我们，例外情况是什么。“我有一个例外”几乎没有有用的信息。@Fildor抱歉！这里有一个例外：java.io.IOException:Stream在sun.nio.cs.StreamDecoder.readBytes（StreamDecoder.java:283）在sun.nio.cs.StreamDecoder.implRead（StreamDecoder.java:325）在java.io.BufferedInputStream.GetBufiOpen（BufferedInputStream.java:162）在java.io.BufferedInputStream.read（BufferedInputStreamDecoder.java:325）在java在java.io.InputStreamReader.read（InputStreamReader.java:184）在java.io.BufferedReader.fill（BufferedReader.java:154）在java.io.BufferedReader.readLine（BufferedReader.BufferedReader）在java.io.BufferedReader.readLine（BufferedReader.BufferedReader）在java.io.InputStreamReader.read（InputStreamReader.java:184）在java.io.io.io.BufferedReader，现在试一试。@BharathRallapalli拼写错误不是问题所在。我正在使用Eclipse，它会告诉我是否存在与问题无关的书写错误。@ViliamBúr请详细说明。将
if
块替换为
switch case
块的好处是，如果多个分支测试同一个表达式，则表达式n只计算一次。在这种特定情况下，表达式是
command.equals（“add”）
，并且在循环中只计算一次。对字符串值重复调用
equals
方法可能效率低下，但它不会引发NoSChelementException，这就是问题所在。