Multiplication in Java

For many situations, the int data type will be adequate for storing integer variables. It can hold values between (roughly) + or - 2 billion. You can multiply two integers as follows:

UBUNTU > cat prog7.java
public class prog7
{
public static void main (String args[])
  {
  // Declare 2 integers:
  int num1 = 1234;
  int num2 = 4321;

  // Multiply them together:
  int num3 = num1 * num2;

  // Display the result:
  System.out.println("num1 = " + num1);
  System.out.println("num2 = " + num2);
  System.out.println("num1 * num2 = " + num3);
  }
}
UBUNTU > javac prog7.java
UBUNTU > java prog7
num1 = 1234
num2 = 4321
num1 * num2 = 5332114
UBUNTU >

... but what happens if the result is too big to store in an int variable?

UBUNTU > cat prog8.java
public class prog8
{
public static void main (String args[])
  {
  // Declare 2 integers:
  int num1 = 123456;
  int num2 = 654321;

  // Multiply them together:
  int num3 = num1 * num2;

  // Display the result:
  System.out.println("num1 = " + num1);
  System.out.println("num2 = " + num2);
  System.out.println("num1 * num2 = " + num3);
  }
}
UBUNTU > javac prog8.java
UBUNTU > java prog8
num1 = 123456
num2 = 654321
num1 * num2 = -824525248
UBUNTU >

According to my calculator, the result should be 80,779,853,376 so some arithmetic overflow must have taken place. As soon as I find out how to handle this, I will do a worked example to demonstrate.

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