Java Type Casting

Type casting means converting one data type into another. For example, turning an int into a double.

In Java, there are two main types of casting:

Widening Casting (automatic) - converting a smaller type to a larger type size
byte -> short -> char -> int -> long -> float -> double
Narrowing Casting (manual) - converting a larger type to a smaller type size
double -> float -> long -> int -> char -> short -> byte

Widening Casting

Widening casting is done automatically when passing a smaller size type into a larger size type.

This works because there is no risk of losing information. For example, an int value can safely fit inside a double:

Example

public class Main {
  public static void main(String[] args) {
    int myInt = 9;
    double myDouble = myInt; // Automatic casting: int to double

    System.out.println(myInt);    // Outputs 9
    System.out.println(myDouble); // Outputs 9.0
  }
}

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Narrowing Casting

Narrowing casting must be done manually by placing the type in parentheses () in front of the value.

This is required because narrowing may result in data loss (for example, dropping decimals when converting a double to an int):

Example

public class Main {
  public static void main(String[] args) {
    double myDouble = 9.78d;
    int myInt = (int) myDouble; // Manual casting: double to int

    System.out.println(myDouble); // Outputs 9.78
    System.out.println(myInt);    // Outputs 9
  }
}

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Real-Life Example

Here is a real-life example of type casting. We calculate the percentage of a user's score in relation to the maximum score in a game.

We use type casting to make sure that the result is a floating-point value, rather than an integer:

Example

// Set the maximum possible score in the game to 500
int maxScore = 500;

// The actual score of the user
int userScore = 423;

/* Calculate the percentage of the user's score in relation to the maximum available score.
Convert userScore to double to make sure that the division is accurate */
double percentage = (double) userScore / maxScore * 100.0d;

System.out.println("User's percentage is " + percentage);

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