Type Casting (Implicit & Explicit)

Type casting in Java is the process of converting one data type into another. It is commonly used when assigning values between variables of different data types. Understanding type casting is crucial to avoid data loss, compilation errors, and runtime bugs, and it is a frequent interview topic.

What Is Type Casting?

• Converting a value from one data type to another
• Mainly applicable to primitive data types
• Can be automatic or manual

Types of Type Casting in Java

Java supports two types of type casting:

1. Implicit Type Casting (Widening)
2. Explicit Type Casting (Narrowing)

1. Implicit Type Casting (Widening)

What Is Implicit Casting?

• Automatically performed by Java
• Converts smaller data type to larger data type
• No data loss
• Safe conversion

Order of Widening

byte → short → int → long → float → double
char → int → long → float → double
          

Example

int a = 10;
double b = a;   // implicit casting
          

Why it works: An int fits safely inside a double.

More Examples

byte b = 20;
int i = b;
char ch = 'A';
int ascii = ch;
          

Why Implicit Casting Matters

• Prevents unnecessary code
• Improves readability
• Safe and compiler-controlled

2. Explicit Type Casting (Narrowing)

What Is Explicit Casting?

• Done manually by the programmer
• Converts larger data type to smaller data type
• Possible data loss
• Requires casting operator

Syntax

targetType variable = (targetType) value;
          

Example

double d = 10.75;
int i = (int) d;
          

Output: i = 10 (decimal part lost)

More Examples

int i = 130;
byte b = (byte) i;  // overflow
          

Result: b = -126

Type Casting with char

char ch = 'A';
int x = ch;        // implicit
char c = (char) x; // explicit
          

Data Loss in Explicit Casting

• Decimal truncation
• Overflow or underflow
• Unexpected results

int num = 300;
byte b = (byte) num;
          

Type Casting Rules (Important)

• Implicit casting → safe
• Explicit casting → programmer responsibility
• boolean cannot be cast to or from any other type
• Casting does not change original variable

Type Casting vs Type Conversion

• Casting → done by programmer
• Conversion → automatic (compiler-driven)

Common Beginner Mistakes

• Assuming explicit casting rounds values
• Ignoring overflow scenarios
• Casting boolean values
• Forgetting parentheses
• Confusing casting with parsing

Interview-Ready Answers

Short Answer

Type casting in Java is converting one data type into another, either implicitly or explicitly.

Detailed Answer

Java supports implicit type casting where smaller data types are automatically converted to larger types, and explicit type casting where larger data types are manually converted to smaller types using casting operators, which may cause data loss.

Key Takeaway

Implicit casting is safe and automatic, while explicit casting is powerful but risky. Always be cautious of data loss and overflow when performing explicit type casting.