In Java, a wrapper class is a class that wraps or encapsulates a primitive data type, providing it with a set of methods and behaviors that are not available to the primitive data type. Each primitive data type in Java has a corresponding wrapper class, as listed below:

• Byte for byte
• Short for short
• Integer for int
• Long for long
• Float for float
• Double for double
• Boolean for boolean
• Character for char

Wrapper classes are commonly used in situations where you need to work with primitive data types as objects, such as in collection classes like ArrayList and HashMap. They are also useful for adding additional functionality to primitive data types, such as parsing and formatting.

Wrapper classes can be instantiated in the same way as any other class in Java, using the new operator and the appropriate constructor. However, Java also provides a feature called autoboxing, which allows you to convert between primitive data types and their corresponding wrapper classes automatically. For example, you can assign an int value to an Integer variable without having to explicitly create an Integer object.

Wrapper classes also provide a range of useful methods for working with primitive data types, such as parseInt() and parseDouble() for converting strings to numerical values, and toString() for converting numerical values to strings.

Here is an example of using wrapper classes in Java:

Integer x = 10; // autoboxing from int to Integer
Double y = 10.5; // autoboxing from double to Double

int z = x.intValue(); // unboxing from Integer to int
double w = y.doubleValue(); // unboxing from Double to double

String s = "20";
int a = Integer.parseInt(s); // parsing a string to an int value

In this example, we use autoboxing to assign an int value to an Integer variable and a double value to a Double variable. We then use unboxing to convert the Integer and Double objects back to their corresponding primitive data types. Finally, we use the parseInt() method of the Integer class to parse a string to an int value.