实现try / catch块

Question

So I am working on a guessing number game that uses a try/catch block to catch (this is homework). If the user enters a non-integer value or a number that is below or above the given range (in this case 1-10).

But I am having issues understanding/properly placing the try catch block I read on how it works but when I try to implement it into my simple code it just seems to be ignored.

Here is the code

//import statements
import java.util.*;     //for scanner class


// class beginning
class  Guess {
    public static void main(String[] args ) { 
        //Declare variables area

        int secretNumber, guess;

        secretNumber = (int) (Math.random() * 10 + 1);           

        Scanner keyboard = new Scanner(System.in);


        // beginning message to user to explain the program
        System.out.println("Welcome to my guess a number program!");
        System.out.println("Please enter in a number to begin guess what the secret number is(1-10): ");   

        //Collect inputs from user or read in data here

        System.out.println("Enter a guess (1-10): ");
        try {
            guess = keyboard.nextInt();
            if (guess < 1 || guess > 10){
            }
        } catch (InputMismatchException e) {
            guess= keyboard.nextInt();
            System.out.println("Not a valid integer");
        }
        //Echo input values back to user here



        //main code and calculations to do
        do {

            if (guess < 1 || guess > 10) {
                System.out.println("Your guess is not in the corre try again.");
                guess = keyboard.nextInt();
            }
            if (guess == secretNumber) {
                System.out.println("Your guess is correct. Congratulations!");
                guess = keyboard.nextInt();
            } else if (guess < secretNumber) {
                System.out
                        .println("Your guess is smaller than the secret number.");
                guess = keyboard.nextInt();
            } else if (guess > secretNumber) {
                System.out
                        .println("Your guess is greater than the secret number.");
                guess = keyboard.nextInt();
            }
        } while (guess != secretNumber);


        //End program message
        System.out.println();
        System.out.println("Hope you enjoyed using this program!");
    }// end main method 


}// end class

It doesn't display "Your guess is correct. Congratulations!" when you guess the right number.

Am I implementing the try catch block correctly? If not how do I and can it be explained so I can do the second one where it catches the float, string and anything not a int.

what it does do

• it correctly randomizes from 1-10
• the program does check to see if it is within the given range

EDIT below is the updated code my only issue I have with it now is that I can't figure out how to apply another catch if a user just hits enter without entering anything I assume I'd need to take the input from user turn it into a string then compare?

    //import statements
import java.util.*;     //for scanner class


 // class beginning
public class Guess {
public static void main(String[] args ) {
    //Declare variables area
    int guess, secretNumber =  (int) (Math.random() * 10 + 1), lowGuess,highGuess;
    Scanner keyboard = new Scanner(System.in);

    // beginning message to user to explain the program
    System.out.println("Welcome to my guessing number program!");
    System.out.println("Please enter in a number to start guessing(enter in a number between 1-10): ");

    //main code and calculations to do
    guess = 0;
    lowGuess = 0;
    highGuess = 11;
    do {
        try {
            guess = keyboard.nextInt();
            if (guess < 1 || guess >10){
                System.out.println("Your guess is not in the correct range try again.");
            }
            else if(guess == secretNumber){
                System.out.println("Your guess is correct. Congratulations!");
            }
            else if(guess < secretNumber && guess <= lowGuess){
                System.out.println("The number you entered is either the same entered or lower please re-enter");
            }
            else if (guess < secretNumber && guess > lowGuess){
                lowGuess = guess;
                System.out.println("Your guess is smaller than the secret number.");
            }
            else if ( guess > secretNumber && guess >= highGuess ){
                System.out.println("The number you entered is either the same entered or higher please re-enter");
            }
            else if (guess > secretNumber && guess < highGuess){
                highGuess = guess;
                System.out.println("Your guess is greater than the secret number.");
            }
        } catch (InputMismatchException e) {
            System.out.println("Not a valid input please re-enter");
            keyboard.next();
            guess = 0;
        }
    } while (guess != secretNumber);

    //End program message
    System.out.println();
    System.out.println("Hope you enjoyed using this program!");
}// end main method


}// end class

Answer 1

This is another approach, but using Exceptions. Please, read this page to understand how try/catch block works.

//import statements
import java.util.*;     //for scanner class


// class beginning
class  Guess {
public static void main(String[] args ) { 
//Declare variables area
int secretNumber, guess;

secretNumber = (int) (Math.random() * 10 + 1);

Scanner keyboard = new Scanner(System.in);


// beginning message to user to explain the program
System.out.println("Welcome to my guess a number program!");
System.out.println("Please enter in a number to begin guess what the secret number is(1-10): ");

//Collect inputs from user or read in data here


//main code and calculations to do
do {


  System.out.println("Enter a guess (1-10): ");
  try {
    guess = keyboard.nextInt();
    if (guess < 1 || guess > 10){
      throw new Exception("Number must be  between 1 and 10");
    }else if(guess == secretNumber){
   throw new Exception("YOU WIN");
  }
  else if (guess < secretNumber){
   throw new Exception("NUMBER IS +");
  }
  else if (guess > secretNumber){
  throw new Exception("NUMBER IS -");
  }
} catch (InputMismatchException e)
{
  System.println("mustbeanumber");
}
catch(Exception e)
{
 System.out.println(e.getMessage());
}

} while (guess != secretNumber);


//End program message
System.out.println();
System.out.println("Hope you enjoyed using this program!");
}// end main method 


}// end class` 

Answer 2

What do you want to do here ?

if (guess < 1 || guess > 10) {
}

You should try something like this :

public class Guess {
    static int guess, secretNumber =  (int) (Math.random() * 10 + 1);
    static Scanner keyboard = new Scanner(System.in);

    public static void main(String[] args ) { 
        do {
            try {       
                guess = keyboard.nextInt();
                if (guess < 1 || guess >10){
                    System.out.println("Your guess is not in the corre try again.");
                }
                if(guess == secretNumber){
                    System.out.println("Your guess is correct. Congratulations!");
                }
                else if (guess < secretNumber){
                    System.out.println("Your guess is smaller than the secret number.");
                }
                else if (guess > secretNumber){ 
                    System.out.println("Your guess is greater than the secret number.");                                     
                }
            } catch (InputMismatchException e) {
                System.out.println("Not a valid integer");
            }
        } while (guess != secretNumber);
    }
}

EDIT : You have to put a piece of code which could maybe throw an exception, in the scope of the try block. It is state of the art to know which part of the code to put in the try block (not too much nor too less).

in-between the try and catch you have your main code/calculations to do and then you close it off and end with the catch to see if after all that if what was entered was valid?

You could always catch the exceptions at top level like you're saying here, but in practice that's not the way to do it. Because when an exception occurs and you don't catch it there will be a process called stack unwinding.

It's really important to understand how stack unwinding works in order to understand what's happening.

You can find information about how this process works here : Explanation of stack unwinding . It explains stack unwinding in C++ but I expect it to be (exactly) the same in Java.