如何使用If语句校验输入必须为整数且不可输入英文单词？

Hey there, let's work through this input validation problem. First off, the big issue with your current code is that sc.nextInt() will throw an InputMismatchException the second someone enters non-integer content (like English words) — that means your if condition never even runs! Let's fix this properly while leaning into if statements for the validation logic.

Core Approach #

We need to:

• Read input as a string first (to avoid immediate exceptions)
• Use if statements to check if the string can be safely converted to an integer (which automatically rules out English words)
• Add extra checks if needed (like ensuring the integer is positive for weight)
• Only proceed with business logic if all checks pass

Fixed Code Example #

Here's a revised version of your code with proper validation:

import java.util.Scanner;

// Assume your existing Salad class, menu array, etc. are already defined
public class OrderValidation {
    private static Scanner sc = new Scanner(System.in);

    public static void main(String[] args) {
        // Example placeholder values for your existing variables
        int itemNum = 1;
        Object[] menu = new Object[]{new Salad()};
        Object[] orderedItem = new Object[10];
        int TtlOrderNum = 0;

        System.out.print("Enter weight (must be an integer): ");
        String userInput = sc.nextLine();

        // First check: Is the input a valid integer (no English words allowed)?
        if (userInput.matches("^-?\\d+$")) {
            int numWeight = Integer.parseInt(userInput);
            
            // Second check: Ensure weight is a positive integer (makes sense for a salad!)
            if (numWeight > 0) {
                ((Salad) menu[itemNum - 1]).setWeight(numWeight);
                System.out.println(menu[itemNum - 1].showOrderDetails());
                System.out.println("-------------------------------------------");
                System.out.println("Total No. of items ordered :");
                orderedItem[TtlOrderNum] = menu[itemNum - 1];
                TtlOrderNum += 1;
                Continue(); // Your custom continue method
            } else {
                System.out.println("Error: Weight must be a positive integer!");
            }
        } else {
            System.out.println("Error: Input must be an integer — no English words or other non-numeric content allowed!");
        }
    }

    // Mock implementation of your Continue method
    private static void Continue() {
        System.out.println("Proceeding with order...");
    }
}

// Mock Salad class for context
class Salad {
    private int weight;
    public void setWeight(int weight) {
        this.weight = weight;
    }
    public String showOrderDetails() {
        return "Salad Weight: " + weight + "g";
    }
}

Key Details Explained #

• Reading as String: Using sc.nextLine() lets us capture the entire input, so we can validate it before trying to convert to an integer.
• Regex Check: The matches("^-?\\d+$") condition uses a regular expression to ensure:
  • ^ = start of the string, $ = end of the string (no extra characters allowed)
  • -? = optional negative sign (remove this if you don't allow negative weights)
  • \\d+ = one or more digits (so no letters or symbols can slip through)
• Nested Ifs: We first confirm the input is an integer, then check if it's logically valid (positive weight) before executing your order logic.

Alternative: Try-Catch + If (No Regex) #

If you prefer not to use regular expressions, you can use a try-catch block paired with if statements to validate:

System.out.print("Enter weight (must be an integer): ");
String userInput = sc.nextLine();
int numWeight = 0;
boolean isValid = true;

if (userInput.isEmpty()) {
    isValid = false;
} else {
    try {
        numWeight = Integer.parseInt(userInput);
        // Extra check: Make sure all characters are digits (or a leading minus)
        if (!userInput.replace("-", "").matches("\\d+")) {
            isValid = false;
        }
    } catch (NumberFormatException e) {
        isValid = false;
    }
}

if (isValid && numWeight > 0) {
    // Execute your order logic here
} else {
    System.out.println("Error: Input must be a positive integer — no English words allowed!");
}

内容的提问来源于stack exchange，提问作者Karl