用字符串Java处理错误

Question

I'm trying to add error handling to my java program if anything but the options and String/char are entered. I mainly need it for if a String is entered. I've tried to do the while(true) but I don't really understand that. I also added !(kb.hasNextInt()) to my line while (choice < 1 && choice > 4 ) but that didn't work either. So I just need help adding error handling to my program. Thanks!

here's my code

import java.util.*;

public class HeroesVersusMonsters 
{
   private static Hero hero;
   private static Monster monster;
   private static Random rand = new Random();


   public static void main(String[] args)
   {
      Scanner kb = new Scanner(System.in);
      do
      {
         System.out.println("---------------------------------------");
         System.out.println("\tChoose your type of hero");
         System.out.println("---------------------------------------");
         System.out.println("\t1. Warrior");
         System.out.println("\t2. Sorceress");
         System.out.println("\t3. Thief");
         System.out.println("\t4. Snake");
         System.out.println();
         System.out.print("Choice --> ");

         int choice = kb.nextInt();
         kb.nextLine();

         while (choice < 1 && choice > 4 )
         {
            System.out.println("\n" + choice + " is not an option. Please try again.");
            System.out.print("Choice --> ");

            choice = kb.nextInt();
            kb.nextLine();
            System.out.println();
         }


         switch (choice)
         {
            case 1:
               hero = new Warrior();
               break;
            case 2:
               hero = new Sorceress();
               break;
            case 3:
               hero = new Thief();
               break;
            case 4:
               hero = new Snake();
               break;
         }
         switch (rand.nextInt(3))
         {
            case 0:
               monster = new Ogre("Shrek the Ogre");
               break;
            case 1:
               monster = new Skeleton("Bones the Skeleton");
               break;
            case 2:
               monster = new Gremlin("Dobby the Gremlin");
               break;
         }
         System.out.println();
         System.out.println(hero.name + ", you will be fighting against " + monster.getName() + "!!!");
         System.out.println();

         while (hero.getHits() > 0 && monster.getHits() > 0)
         {
            hero.attack(monster);
            monster.attack(hero);
         }

         System.out.print("Would you like to play again? (yes / no) ");

         String play = kb.nextLine().toLowerCase();
         play = play.trim();

         if (play.equals("no"))
            break;
         else
            System.out.println();

      }
      while (true);
   }
}

Answer 1

Please look closly to your condition of inner while loop.

 while (choice < 1 && choice > 4 )

Means loop will work until choice<1 and choice>4 remains true.

Is it exactly what you want?

I think No because what if input is 5 it is true for >4 but false for <1 what you want is you need to loop things until user enters correct input.

Am I right?

So what you need to do is just change condition like this

while(choice<1 || choice>4)

As Jared stated.

One more thing I want to suggest you don't you think you should break; external loop while user enters wrong input.(No problem)

You can do one this also.

ArrayList<Integer> ar=new ArrayList<Integer>(4);
ar.add(1);
ar.add(2);
ar.add(3);
ar.add(4);
while(true)
{
if(ar.contains(choice))
{
//Go On
}
else
{
//Print old stuff
}
}

Answer 2

You should check out the Java regex:

if(choice.toString().matches("[0-9]+"))
{
      //continue
}

else
{
     //error message
}

Answer 3

Here is what your main method should look like:

public static void main(String ...args){
    final Scanner scanner = new Scanner(System.in);

    while(true){
        final Hero hero = promptHero(scanner);
        final Monster monster = getRandomMonster();

        fight(hero, monster);
        if(!playAgain(scanner))
            break;
    }
}

Now write the static methods promptHero , getRandomMonster , fight , and playAgain (which should return true if you want to play again).

Here is what your promptHero method should look like (to properly handle bad input):

private static Hero promptHero(final Scanner scanner){
    while(true){
        System.out.println("---------------------------------------");
        System.out.println("\tChoose your type of hero");
        System.out.println("---------------------------------------");
        System.out.println("\t1. Warrior");
        System.out.println("\t2. Sorceress");
        System.out.println("\t3. Thief");
        System.out.println("\t4. Snake");
        System.out.println();
        System.out.print("Choice --> ");

        try{
            final int choice = scanner.nextInt();

            if(choice < 1 || choice > 4)
                System.out.println("\n" + choice + 
                    " is not an option. Please try again.");
            else
                return getHero(choice); //return the hero
        } catch(InputMismatchException ime){
            final String line = scanner.nextLine();// need to advance token
            System.out.println("\n" + line + 
                    " is not an option. Please try again.");
        }
    }
}
private static Hero getHero(final int choice){
    switch (choice){
    case 1:
        return new Warrior();
    case 2:
        return new Sorceress();
    case 3:
        return new Thief();
    case 4:
        return new Snake();
    }
    return null;
}