Data Type Casting in Java

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Casting in Java refers to converting a variable from one data type to another. Java supports both implicit (automatic) and explicit (manual) casting.

Implicit Casting (Automatic)

Implicit casting happens when you assign a value of smaller data type to a larger data type. For example, assigning an int to a long:

int smallNumber = 10;
long largeNumber = smallNumber; // implicit casting

Explicit Casting (Manual)

Explicit casting is required when you are assigning a value of larger data type to a smaller data type. For example, assigning a double to an int:

double decimalNumber = 10.5;
int wholeNumber = (int) decimalNumber; // explicit casting

Here is a full example, including both implicit and explicit casting, using various data types:

public class DataTypeCasting {

    public static void main(String[] args) {

        // Implicit Casting
        char aChar = 'A'; // size: 16-bit
        int aInt = aChar; // size: 32-bit
        System.out.println("Implicit Casting: char to int: " + aInt); // 65 (ASCII value of 'A')

        long aLong = aInt; // size: 64-bit
        System.out.println("Implicit Casting: int to long: " + aLong); // 65

        float aFloat = aLong; // size: 32-bit
        System.out.println("Implicit Casting: long to float: " + aFloat); // 65.0

        double aDouble = aFloat; // size: 64-bit
        System.out.println("Implicit Casting: float to double: " + aDouble); // 65.0


        // Explicit Casting
        aFloat = 65.65f; // size: 32-bit
        aLong = (long) aFloat; // size: 64-bit
        System.out.println("Explicit Casting: float to long: " + aLong); // 65

        aInt = (int) aLong; // size: 32-bit
        System.out.println("Explicit Casting: long to int: " + aInt); // 65

        aChar = (char) aInt; // size: 16-bit
        System.out.println("Explicit Casting: int to char: " + aChar); // A

        byte aByte = (byte) aInt; // size: 8-bit
        System.out.println("Explicit Casting: int to byte: " + aByte); // 65
    }
}

In this example:

  • We implicitly cast from char to int to long to float to double, each being of a larger data type.
  • We explicitly cast back down from float to long to int to char and finally to byte, each being of a smaller data type.
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