Master Core Java Programming From Scratch

What is Type Conversion?

Type conversion is the process of converting a value from one data type to another data type.

Java supports both implicit and explicit type conversion. The conversion performed depends on the relationship between the source and target data types.

Types of Type Conversion

int number = 100;

long value = number;

double price = 99.99;

int value = (int) price;

1. Widening Conversion

Widening conversion occurs when a value is converted from a type with a smaller range to a type with a larger range.

For compatible primitive numeric types, Java can perform this conversion automatically.

int number = 100;

long value = number;

System.out.println(value);

Common Numeric Widening Path

byte
  ↓
short
  ↓
int
  ↓
long
  ↓
float
  ↓
double

Widening Example

public class DataTypes {

    public static void main(String[] args) {

        byte a = 10;

        short b = a;

        int c = b;

        long d = c;

        float e = d;

        double f = e;

        System.out.println(f);

    }

}

2. Narrowing Conversion

Narrowing conversion converts a value from a larger numeric type to a smaller numeric type.

Because information can be lost, Java requires an explicit cast.

double number = 100.75;

int value = (int) number;

System.out.println(value);

Explicit Casting

Explicit casting is performed by placing the target type in parentheses before the value.

double salary = 45000.75;

int roundedValue = (int) salary;

The general syntax is:

targetType variableName = (targetType) value;

Data Loss During Conversion

Narrowing conversion can cause data loss because the target type may not be able to represent the complete source value.

double value = 123.987;

int result = (int) value;

System.out.println(result);

Output:

123

Integer Overflow During Narrowing

If a value is outside the range of the target integer type, narrowing can produce a value that differs significantly from the original value.

int number = 130;

byte value = (byte) number;

System.out.println(value);

char and Numeric Conversion

A char can participate in numeric conversions because it is an unsigned 16-bit integral type.

char letter = 'A';

int code = letter;

System.out.println(code);

The output is:

65

Integer Division

Type conversion is particularly important when performing arithmetic operations involving integers.

int a = 5;

int b = 2;

double result = a / b;

The result is 2.0, not 2.5, because the division is performed using integer operands before the result is assigned to the double.

To obtain a floating-point result, convert one operand:

int a = 5;

int b = 2;

double result = (double) a / b;

System.out.println(result);

Converting Values to String

Java provides several ways to create a string representation of a value.

int number = 100;

String text = String.valueOf(number);

System.out.println(text);

Converting String to Number

Wrapper classes provide parsing methods for converting text into primitive numeric values.

String text = "123";

int number = Integer.parseInt(text);

System.out.println(number + 10);

Output:

133

String to Double

String text = "45.75";

double value = Double.parseDouble(text);

System.out.println(value);

String to Boolean

String text = "true";

boolean value = Boolean.parseBoolean(text);

System.out.println(value);

Primitive and Wrapper Types

Java provides wrapper classes for primitive types.

Autoboxing

Autoboxing automatically converts a primitive value into its corresponding wrapper object when required.

int number = 100;

Integer object = number;

Unboxing

Unboxing converts a wrapper object back into its corresponding primitive type.

Integer object = 100;

int number = object;

Type Conversion Quick Reference

Common Mistakes