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Java Program to Multiply Two Numbers

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Java multiplies numbers with the * operator: product = first * second. This page multiplies whole and decimal numbers, reads them from the user, and shows how to catch results that are too large for their type.

1. Multiply Two Numbers Using a Method

The multiply() method takes two double values, so it works for both whole and decimal numbers.

MultiplyNumbers.java 
public class MultiplyNumbers {

    static double multiply(double a, double b) {
        return a * b;
    }

    public static void main(String[] args) {
        System.out.println("20 x 40 = " + multiply(20, 40));
        System.out.println("10.5 x 20.75 = " + multiply(10.5, 20.75));
        System.out.println("-6 x 7 = " + multiply(-6, 7));
    }
}
Output
20 x 40 = 800.0
10.5 x 20.75 = 217.875
-6 x 7 = -42.0

2. Multiply Two Numbers with User Input

MultiplyNumbersInput.java 
import java.util.Scanner;

public class MultiplyNumbersInput {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter first number: ");
        double first = scanner.nextDouble();
        System.out.print("Enter second number: ");
        double second = scanner.nextDouble();
        scanner.close();

        System.out.println("Product: " + (first * second));
    }
}
Output (with sample input)
Enter first number: 20.50
Enter second number: 50.75
Product: 1040.375

3. Detect Overflow with Math.multiplyExact()

Multiplying two large int values can overflow and silently give a wrong answer. Math.multiplyExact() throws an ArithmeticException instead, so the error is not hidden.

MultiplyExact.java 
public class MultiplyExact {
    public static void main(String[] args) {
        int a = 100_000;
        int b = 50_000;

        System.out.println("a * b with int:  " + (a * b));          // overflows
        System.out.println("a * b with long: " + ((long) a * b));   // correct

        try {
            System.out.println(Math.multiplyExact(a, b));
        } catch (ArithmeticException e) {
            System.out.println("multiplyExact: " + e.getMessage());
        }
    }
}
Output
a * b with int:  705032704
a * b with long: 5000000000
multiplyExact: integer overflow

4. Summary

  • Use the * operator to multiply numbers of any numeric type.
  • A method with double parameters handles both whole and decimal numbers.
  • Products grow fast: cast to long before multiplying large int values.
  • Math.multiplyExact() throws an exception instead of returning an overflowed value.

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