Java Type Casting
Converting between different data types in Java
🔄 What is Type Casting?
Type casting is converting a variable from one data type to another. Java supports automatic conversion (widening) and manual conversion (narrowing) between compatible data types.
// Automatic casting (widening)
int number = 100;
double decimal = number; // int to double
// Manual casting (narrowing)
double price = 19.99;
int dollars = (int) price; // double to int
Output:
number: 100
decimal: 100.0
price: 19.99
dollars: 19
Types of Type Casting
Widening Casting
Automatic conversion to larger type
int num = 50;
double result = num; // AutomaticNarrowing Casting
Manual conversion to smaller type
double num = 50.7;
int result = (int) num; // ManualString Conversion
Convert numbers to strings
int age = 25;
String ageText = String.valueOf(age);Parse Methods
Convert strings to numbers
String text = "123";
int number = Integer.parseInt(text);🔹 Widening Casting (Automatic)
Java automatically converts smaller data types to larger ones:
// Widening casting examples
byte smallNum = 10;
short mediumNum = smallNum; // byte to short
int regularNum = mediumNum; // short to int
long bigNum = regularNum; // int to long
float floatNum = bigNum; // long to float
double doubleNum = floatNum; // float to double
System.out.println("Original byte: " + smallNum);
System.out.println("As double: " + doubleNum);Output:
Original byte: 10
As double: 10.0
🔹 Narrowing Casting (Manual)
You must manually cast when converting to smaller data types:
// Narrowing casting examples
double originalValue = 123.456;
float floatValue = (float) originalValue;
long longValue = (long) originalValue;
int intValue = (int) originalValue;
short shortValue = (short) originalValue;
byte byteValue = (byte) originalValue;
System.out.println("Original: " + originalValue);
System.out.println("As int: " + intValue);
System.out.println("As byte: " + byteValue);Output:
Original: 123.456
As int: 123
As byte: 123
🔹 String Conversions
Converting between strings and numbers:
// Number to String
int age = 25;
double price = 19.99;
boolean isActive = true;
String ageText = String.valueOf(age);
String priceText = String.valueOf(price);
String statusText = String.valueOf(isActive);
// String to Number
String numberText = "42";
String decimalText = "3.14";
int parsedInt = Integer.parseInt(numberText);
double parsedDouble = Double.parseDouble(decimalText);
System.out.println("Age as text: " + ageText);
System.out.println("Parsed number: " + parsedInt);Output:
Age as text: 25
Parsed number: 42
🔹 Common Casting Scenarios
Practical examples of type casting:
// Calculating average (int division problem)
int total = 100;
int count = 3;
double average = (double) total / count; // Cast to get decimal result
// Getting whole dollars from price
double productPrice = 29.99;
int wholeDollars = (int) productPrice;
// Converting user input
String userInput = "25";
int userAge = Integer.parseInt(userInput);
System.out.println("Average: " + average);
System.out.println("Whole dollars: " + wholeDollars);
System.out.println("User age: " + userAge);Output:
Average: 33.333333333333336
Whole dollars: 29
User age: 25
Important Notes:
- Narrowing casting may lose precision or data
- Always cast when going from larger to smaller types
- Use parse methods carefully - they can throw exceptions
- Widening casting is always safe