Wrapper class in Java

In Java, a wrapper class is a class that provides a way to represent primitive data types (int, char, boolean, etc.) as objects. The Java language specification requires that every primitive data type has a corresponding wrapper class. In this article, we will explore the concept of wrapper classes in Java and their usage.

Overview of Wrapper Classes

In Java, a wrapper class is a class that provides a way to represent primitive data types as objects. The following table shows the primitive data types and their corresponding wrapper classes:

Primitive Data Type	Wrapper Class
byte	Byte
short	Short
int	Integer
long	Long
float	Float
double	Double
char	Character
boolean	Boolean

Each wrapper class provides a set of methods that can be used to manipulate the wrapped primitive value. These methods include conversion methods, comparison methods, and mathematical operations.

Wrapper classes are immutable, meaning that their values cannot be changed once they are created. To change the value of a wrapper class, a new instance must be created with the new value.

Usage of Wrapper Classes

Wrapper classes are primarily used in situations where an object representation of a primitive value is needed. For example, Java collections (ArrayList, HashMap, etc.) can only store objects. Therefore, if we want to store primitive values in a collection, we need to use the corresponding wrapper class.

Wrapper classes are also useful when we want to pass primitive values as arguments to methods that expect objects. For example, the System.out.println() method expects an object argument. If we want to print a primitive value, we can use the corresponding wrapper class to create an object representation of the value.

Another usage of wrapper classes is in the implementation of generics. Generics are a way to create classes and methods that can work with any type of object. Since primitive data types are not objects, they cannot be used with generics. However, by using the corresponding wrapper class, we can create a generic class or method that can work with primitive values.

Autoboxing and Unboxing

Java provides a feature called autoboxing and unboxing that allows us to convert between primitive data types and their corresponding wrapper classes automatically. Autoboxing is the automatic conversion of a primitive value to its corresponding wrapper class, while unboxing is the automatic conversion of a wrapper class to its corresponding primitive value.

Here is an example of autoboxing:

int i = 10;
Integer integer = i; // autoboxing

In this example, the int value 10 is automatically converted to an Integer object.

Here is an example of unboxing:

Integer integer = 10;
int i = integer; // unboxing

In this example, the Integer object 10 is automatically converted to an int value.

Autoboxing and unboxing can be useful in situations where we need to work with both primitive values and their corresponding wrapper classes.

Conclusion

Wrapper classes are a fundamental concept in Java that provides a way to represent primitive data types as objects. They are useful in situations where an object representation of a primitive value is needed, such as in Java collections or when passing primitive values as arguments to methods that expect objects. Autoboxing and unboxing provide a convenient way to convert between primitive data types and their corresponding wrapper classes.