java如何根据扫描器输入循环此操作？

Question

我正在为我的第二学期java课程做一个作业，我在想如何最好地循环这个过程时遇到了一点困难。我需要在每个循环开始时弹出“选择选项”行，允许用户输入a、b、c或q。如果用户选择a、b、c，我希望它执行操作，然后返回“选择选项”行并重新开始，如果用户输入q，则应退出。我应该用什么样的环来做这个

public void go() throws Exception  {
Scanner kb = new Scanner(System.in);
ArrayList<Task> list = new ArrayList<Task>();
TaskManager taskMgr = new TaskManager();

    System.out.println("Welcome to MyTaskManager");
    System.out.println("choose an option \n a: Add a new item \n b: Display tasks by date \n c: Display tasks by keyword \n q: quit");
    System.out.println("Enter your choice");
    String choice = kb.nextLine();  
         if (choice.equalsIgnoreCase("a")) {
        taskMgr.makeTasks();
    }
    else if (choice.equalsIgnoreCase("b")) {
        System.out.println("enter the date you wish to view: ");
         SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
        String date=kb.nextLine();
        Date dueDate = sdf.parse(date);
        taskMgr.findTasksByDate(dueDate);
         taskMgr.displayTaskReportByDate(dueDate);

    }
    else if (choice.equalsIgnoreCase("c")) {
        System.out.println(" Enter a keyword: ");
        String keyword=kb.nextLine();
        System.out.println("Task that contain the term "+keyword);
        taskMgr.findTasksByKeyword(keyword);
         taskMgr.displayTaskReportByKeyword(keyword);

    }
    else if (choice.equalsIgnoreCase("q")) {
        System.exit(0);
    }
    else {
         System.exit(0);
    }
}

Answer 1

你好像错过了一个循环。因此，要使用您当前的代码-

while (true) { // <  or for(;;) {
    System.out.println("choose an option \n a: Add a new item \n b: Display tasks by date \n c: Display tasks by keyword \n q: quit");
    System.out.println("Enter your choice");
    String choice = kb.nextLine();  
    if (choice.equalsIgnoreCase("a")) {
      taskMgr.makeTasks();
    } else if (choice.equalsIgnoreCase("b")) {
      System.out.println("enter the date you wish to view: ");
      SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
      String date=kb.nextLine();
      Date dueDate = sdf.parse(date);
      taskMgr.findTasksByDate(dueDate);
      taskMgr.displayTaskReportByDate(dueDate);
  } else if (choice.equalsIgnoreCase("c")) {
      System.out.println(" Enter a keyword: ");
      String keyword=kb.nextLine();
      System.out.println("Task that contain the term "+keyword);
      taskMgr.findTasksByKeyword(keyword);
      taskMgr.displayTaskReportByKeyword(keyword);
  } else if (choice.equalsIgnoreCase("q")) {
      // System.exit(0);
      break; //<  ends the loop.
  } // no else and quit. we want to loop.
}

Answer 2

您可以使用while(true)循环来实现这一点-它永远不会停止（直到退出）。这是因为while()的括号中通常有一个值，如果循环停止，该值将变为false。有了while(true){ACTION}你就有了经典的无限循环，在计算机科学中经常用于需要用户输入的各种应用程序

public void go() throws Exception  {
Scanner kb = new Scanner(System.in);
ArrayList<Task> list = new ArrayList<Task>();
TaskManager taskMgr = new TaskManager();

System.out.println("Welcome to MyTaskManager");
while(true){
System.out.println("choose an option \n a: Add a new item \n b: Display tasks by date \n c: Display tasks by keyword \n q: quit");
System.out.println("Enter your choice");
String choice = kb.next();  
     if (choice.equalsIgnoreCase("a")) {
    taskMgr.makeTasks();
}
else if (choice.equalsIgnoreCase("b")) {
    System.out.println("enter the date you wish to view: ");
     SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
    String date=kb.nextLine();
    Date dueDate = sdf.parse(date);
    taskMgr.findTasksByDate(dueDate);
     taskMgr.displayTaskReportByDate(dueDate);

}
else if (choice.equalsIgnoreCase("c")) {
    System.out.println(" Enter a keyword: ");
    String keyword=kb.nextLine();
    System.out.println("Task that contain the term "+keyword);
    taskMgr.findTasksByKeyword(keyword);
     taskMgr.displayTaskReportByKeyword(keyword);

}
else if (choice.equalsIgnoreCase("q")) {
    System.exit(0);
}
else {
     System.exit(0);
}
}
}