How to Correctly Divide Two Long Variables in Java

Why does dividing two long variables in Java return 0?

long a = 3004230; 
long b = 6793368; 
long c = (a / b) * 100;

When dividing two long variables in Java, the result is also a long. If the division results in a decimal, it will be truncated to an integer, often resulting in 0. This guide explains why this happens and how to obtain a correct result.

long a = 3004230; 
long b = 6793368; 
double c = ((double) a / b) * 100; // Correctly divides without truncation.

Causes

• Integer Division: In Java, dividing two integers (or long types) will yield an integer result. Any fractional part is discarded, leading to potential issues when the numerator is smaller than the denominator.
• Incorrect Type Casting: If either value is treated as an integer, the division will still follow the integer division rules.

Solutions

• Use floating-point arithmetic by casting at least one of the operands to a double before performing the division. For example: ```java long a = 3004230; long b = 6793368; double c = ((double) a / b) * 100; ```
• Perform the multiplication before the division to maintain precision: ```java long a = 3004230; long b = 6793368; double c = (double) (a * 100) / b; ```

Mistake: Assuming all divisions yield a non-zero result without considering operand types.

Solution: Always check the types of the operands before division. Cast them to double if a non-integer result is expected.

Mistake: Performing multiplication after division which results in less precision.

Solution: Multiply before dividing to preserve precision.