Before you learn about Java Type Casting, make sure you know about Java Data Types.
Type Casting
The process of converting the value of one data type (int, float, double, etc.) to another data type is known as typecasting.
In Java, there are 13 types of type conversion. However, in this tutorial, we will only focus on the major 2 types.
1. Widening Type Casting
2. Narrowing Type Casting
To learn about other types of type conversion, visit Java Type Conversion (official Java documentation).
Widening Type Casting
In Widening Type Casting, Java automatically converts one data type to another data type.
Example: Converting int to double
class Main {
public static void main(String[] args) {
// create int type variable
int num = 10;
System.out.println("The integer value: " + num);
// convert into double type
double data = num;
System.out.println("The double value: " + data);
}
}
Output
The integer value: 10 The double value: 10.0
In the above example, we are assigning the int type variable named num to a double type variable named data.
Here, the Java first converts the int type data into the double type. And then assign it to the double variable.
In the case of Widening Type Casting, the lower data type (having smaller size) is converted into the higher data type (having larger size). Hence there is no loss in data. This is why this type of conversion happens automatically.
Note: This is also known as Implicit Type Casting.
Narrowing Type Casting
In Narrowing Type Casting, we manually convert one data type into another using the parenthesis.
Example: Converting double into an int
class Main {
public static void main(String[] args) {
// create double type variable
double num = 10.99;
System.out.println("The double value: " + num);
// convert into int type
int data = (int)num;
System.out.println("The integer value: " + data);
}
}
Output
The double value: 10.99 The integer value: 10
In the above example, we are assigning the double type variable named num to an int type variable named data.
Notice the line,
int data = (int)num;
Here, the int keyword inside the parenthesis indicates that that the num variable is converted into the int type.
In the case of Narrowing Type Casting, the higher data types (having larger size) are converted into lower data types (having smaller size). Hence there is the loss of data. This is why this type of conversion does not happen automatically.
Note: This is also known as Explicit Type Casting.
Let's see some of the examples of other type conversions in Java.
Example 1: Type conversion from int to String
class Main {
public static void main(String[] args) {
// create int type variable
int num = 10;
System.out.println("The integer value is: " + num);
// converts int to string type
String data = String.valueOf(num);
System.out.println("The string value is: " + data);
}
}
Output
The integer value is: 10 The string value is: 10
In the above program, notice the line
String data = String.valueOf(num);
Here, we have used the valueOf() method of the Java String class to convert the int type variable into a string.
Example 2: Type conversion from String to int
class Main {
public static void main(String[] args) {
// create string type variable
String data = "10";
System.out.println("The string value is: " + data);
// convert string variable to int
int num = Integer.parseInt(data);
System.out.println("The integer value is: " + num);
}
}
Output
The string value is: 10 The integer value is: 10
In the above example, notice the line
int num = Integer.parseInt(data);
Here, we have used the parseInt() method of the Java Integer class to convert a string type variable into an int variable.
Note: If the string variable cannot be converted into the integer variable then an exception named NumberFormatException occurs.
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