验证负输入

Question

I am trying to validate a user input. I don't want the user to enter negative numbers, strings, and doubles number. I only need int. I am only able to validate strings and doubles. Your help will be appreciated.

do {

    System.out.println("How many cappuccino drinks were sold today?");
    if(input.hasNextInt()) {

        cappuccinoDrink = input.nextInt();


            capexpenses = cappuccinoDrink * 1.56;
            capRevenue = cappuccinoDrink * 3.50;
            capProfit = capRevenue - capexpenses;
            isNumber = true;

    }else {
        System.out.println("You didn't didn't enter the require imput");
        isNumber = false;
        input.next();
    }
} while(!isNumber);

Answer 1

Change if(input.hasNextInt()) { to the following:

if(input.hasNextInt() && (cappuccinoDrink = input.nextInt()) >= 0) {
            //removed assignment as it is handled in if statement
            capRevenue = cappuccinoDrink * 3.50;
            capProfit = capRevenue - capexpenses;
            isNumber = true;
}

Answer 2

int cappuccinoDrink;
boolean invalidinput = true;
System.out.println("Please enter a positive integer : ");
while(invalidInput){
   try{
     cappuccinoDrink = input.nextInt();
     if( cappuccinoDrink<= 0) {  
            System.out.println("Please enter a positive integer value: ");
     }
     else{invalidInput=false;}
   }
   catch(InputMismatchException e){
        System.out.println("Please enter a positive integer value: ");
   }
}
        capexpenses = cappuccinoDrink * 1.56;
        capRevenue = cappuccinoDrink * 3.50;
        capProfit = capRevenue - capexpenses;