如何根据扫描仪的输入来循环显示？

Question

I'm working on a assignment for my second semester java class and I'm having a little trouble trying to figure out how best to loop this. I need the "choose an option" line to pop up at the beginning of each loop and allow the user to enter a,b,c or q. If the user picks a,b,c I want to it do the action and then to return to the "choose an option" line and start over and if the user enters q it should quit. What kind of loop should I use for this?

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

You seem to be missing a loop. So, to work with your current code -

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

You can do this with while(true) loop - it never stops (until exit). That is because while() usually has a value in its bracket which changes to false if the loop should stop. with while(true){ACTION} you have the classic infinite loop, used often in computer science for a variety of applications that need user input.

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);
}
}
}