当这个人输入错误的输入时，我不知道如何重新启动循环

Question

Ok so for an assignment I need to make a loop for the user to input a number 1-4 for either rock paper scissors or to end the game, but if they enter in anything other than those I need them to be able to re-enter the number but I can't seem to get my loop to restart or something similar...

Code (It's just my while loop

while(user < 5)
          {
              System.out.println("Please enter in a number");
              computer = generator.nextInt(3) + 1;            
              user = keyboardIn.nextInt();

              //tell the player what was chosen
              if(user == 1)//player is rock
              {
                 System.out.println ("Player is rock");  
              }
              else if (user == 2)//player is paper
              {
                 System.out.println ("Player is paper");
              }
              else if (user == 3) //player is scissors
              {
                System.out.println ("Player is scissors");

              }
              else if (user == 4)
              {
                  System.out.println("Thank you for playing!");
                  break;
              }
              else if (user >= 5)
              {
                  System.out.println(user + " was never an option. \nTry again.");
                  user = keyboardIn.nextInt();
              }

              //tell the player what the computer has chosen
              if(computer == 1)//computer is rock
              {
                 System.out.println ("Computer is rock");
              }
              else if (computer == 2)//computer is paper
              {
                 System.out.println ("Computer is paper");
              }
              else if (computer == 3)//computer is scissors
              {
                 System.out.println ("Computer is scissors");
              }


              //determine winner
              if (user == computer) //tie
              {
                 System.out.println("It is a tie");
              }
              else if (user < computer) //player is rock
              {
                 System.out.println("Computer wins");
              }
              else //computer is scissors
              {
                 System.out.println("Player wins");
              }
              System.out.println();
          }

Answer 1

You can use continue to jump back to the top of the loop. Note, however, that at the top you ask for user input, and on error you do so too; that's one time too many.

Answer 2

You could use

boolean gameOver = false;
while(!gameOver){
    if (user < 5){
     ....
    }
}

and set gameOver = true in each of your game-ending conditions.

Answer 3

Replace the part:

else if (user >= 5)
              {
                  System.out.println(user + " was never an option. \nTry again.");
                  user = keyboardIn.nextInt();
              }

With:

else if (user >= 5)
              {
                  System.out.println(user + " was never an option. \nTry again.");
                  continue;
              }

Basically the continue, brakes the current loop and start over a new one, of course verifying first the condition...

However if you want your code to be a little bit more efficient, in your specific case this would be my way of doing it:

while(true) {
    computer = generator.nextInt(3) + 1; 
    do {
        System.out.println("Please enter in a number");           
        user = keyboardIn.nextInt();
    } while(user>=5 && user<=0);
    //The rest of your code deleting also the last else if statement
 }

This way your code is cleaner and more maintainable. Plus you will be sure that after the code exit from the loop you will definitely have a number between 0 and 4 which would be a valid option