Type conversion in Java with Examples

When you assign value of one data type to another, the two types might not be compatible with each other. If the data types are compatible, then Java will perform the conversion automatically known as Automatic Type Conversion and if not then they need to be casted or converted explicitly. For example, assigning an int value to a long variable.

Widening or Automatic Type Conversion

Widening conversion takes place when two data types are automatically converted. This happens when:

• The two data types are compatible.
• When we assign value of a smaller data type to a bigger data type.

For Example, in java the numeric data types are compatible with each other but no automatic conversion is supported from numeric type to char or boolean. Also, char and boolean are not compatible with each other.

Example:

class Test
{
    public static void main(String[] args)
    {
        int i = 100; 
        
        //automatic type conversion
        long l = i; 
        
        //automatic type conversion
        float f = l; 
        System.out.println("Int value "+i);
        System.out.println("Long value "+l);
        System.out.println("Float value "+f);
    }
}

Output:

Int value 100
Long value 100
Float value 100.0

Narrowing or Explicit Conversion

If we want to assign a value of larger data type to a smaller data type we perform explicit type casting or narrowing.

• This is useful for incompatible data types where automatic conversion cannot be done.
• Here, target-type specifies the desired type to convert the specified value to.

char and number are not compatible with each other. Let’s see when we try to convert one into other.

//Java program to illustrate incompatible data 
// type for explicit type conversion
public class Test
{
  public static void main(String[] argv)
  {
    char ch = 'c';
    int num = 88;
    ch = num;
  }
}

Error:

7: error: incompatible types: possible lossy conversion from int to char
    ch = num;
         ^
1 error

How to do Explicit Conversion?
Example:

//Java program to illustrate explicit type conversion
class Test
{
    public static void main(String[] args)
    {
        double d = 100.04; 
        
        //explicit type casting
        long l = (long)d;
        
        //explicit type casting 
        int i = (int)l; 
        System.out.println("Double value "+d);
        
        //fractional part lost
        System.out.println("Long value "+l); 
        
        //fractional part lost
        System.out.println("Int value "+i); 
    } 
}

Output:

Double value 100.04
Long value 100
Int value 100

While assigning value to byte type the fractional part is lost and is reduced to modulo 256(range of byte).
Example:

//Java program to illustrate Conversion of int and double to byte
class Test
{
    public static void main(String args[]) 
    { 
        byte b; 
        int i = 257; 
        double d = 323.142;
        System.out.println("Conversion of int to byte."); 
        
        //i%256
        b = (byte) i; 
        System.out.println("i = " + i + " b = " + b);
        System.out.println("\nConversion of double to byte.");
        
        //d%256
        b = (byte) d; 
        System.out.println("d = " + d + " b= " + b);
    }
}

Output:

Conversion of int to byte.
i = 257 b = 1

Conversion of double to byte.
d = 323.142 b = 67

Type promotion in Expressions

While evaluating expressions, the intermediate value may exceed the range of operands and hence the expression value will be promoted. Some conditions for type promotion are:

1. Java automatically promotes each byte, short, or char operand to int when evaluating an expression.
2. If one operand is a long, float or double the whole expression is promoted to long, float or double respectively.

Example:

//Java program to illustrate Type promotion in Expressions 
class Test
{ 
    public static void main(String args[]) 
    { 
        byte b = 42; 
        char c = 'a'; 
        short s = 1024;
        int i = 50000;
        float f = 5.67f;
        double d = .1234;
        
        // The Expression
        double result = (f * b) + (i / c) - (d * s);
        
        //Result after all the promotions are done
        System.out.println("result = " + result);
    } 
}

Output:

Result = 626.7784146484375

Explicit type casting in Expressions

While evaluating expressions, the result is automatically updated to larger data type  of the operand. But if we store that result in any smaller data type it generates compile time error, due to which we need to type cast the result.
Example:

//Java program to illustrate type casting int to byte
class Test
{ 
    public static void main(String args[]) 
    { 
        byte b = 50; 
        
        //type casting int to byte
        b = (byte)(b * 2); 
        System.out.println(b);
    }
}

Output

 100

NOTE- In case of single operands the result gets converted to int and then it is type casted accordingly.
Example:

//Java program to illustrate type casting int to byte
class Test
{ 
    public static void main(String args[]) 
    { 
        byte b = 50; 

        //type casting int to byte
        b = (byte)(b * 2); 
        System.out.println(b);
    }
} 

Output

100

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