Type Casting (Widening vs Narrowing), Overflow & Underflow

1Concept

Implicit Casting (Widening): Automatic conversion from smaller to larger types (byte -> short -> int -> long -> float -> double) with zero data loss. Explicit Casting (Narrowing): Manual conversion from larger to smaller types (e.g. (int)3.99), causing decimal truncation or bit overflow. Overflow occurs when arithmetic exceeds Integer.MAX_VALUE, wrapping around to Integer.MIN_VALUE.

2Architecture Diagram

Widening (Safe):    byte ---> short ---> int ---> long ---> float ---> double
Narrowing (Manual): double --(cast)--> float --(cast)--> long --(cast)--> int

3Code Example

public class CastingAndOverflow {
    public static void main(String[] args) {
        int num = 100;
        double dbl = num;
        System.out.println("Widened int to double: " + dbl);

        double price = 99.95;
        int truncatedPrice = (int) price;
        System.out.println("Narrowed double to int: " + truncatedPrice);

        int maxInt = Integer.MAX_VALUE;
        int overflowed = maxInt + 1;
        System.out.println("Max Int: " + maxInt);
        System.out.println("Max Int + 1 (Overflow): " + overflowed);
    }
}

4Expected Output

Widened int to double: 100.0
Narrowed double to int: 99
Max Int: 2147483647
Max Int + 1 (Overflow): -2147483648

5Key Takeaways

• ✓Explicit narrowing casts discard high-order bits or decimal precision.
• ✓Integer arithmetic wraps around silently upon overflow; use Math.addExact() to throw ArithmeticException.
• ✓Java 10+ var infers types statically at compile time.