What is wrapper class and why we need them?

A wrapper class in Java is an object representation of primitive data types. Wrapper classes allow primitive types (e.g., int, double) to be treated as objects.

Examples of Wrapper Classes:

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

Why Do We Need Wrapper Classes?

Object Requirement:
- Many Java classes (e.g., Collections framework) work only with objects, not primitives. Wrapper classes allow you to use primitive values as objects.
List<Integer> numbers = new ArrayList<>(); // Works with Integer, not int numbers.add(10); // Autoboxing converts int to Integer

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List<Integer> numbers = new ArrayList<>(); // Works with Integer, not int
numbers.add(10); // Autoboxing converts int to Integer
Utility Methods:
- Wrapper classes provide useful utility methods like parsing strings to numbers.
int number = Integer.parseInt("123"); // Converts string to int

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int number = Integer.parseInt("123"); // Converts string to int
Default Values in Generics:
- Generic types in Java can only accept objects. Wrapper classes allow you to use primitives in generics.
List<Double> list = new ArrayList<>(); // Double instead of double

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List<Double> list = new ArrayList<>(); // Double instead of double
Null Representation:
- Primitives cannot hold null, but wrapper objects can.
Integer nullableValue = null; // Works

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Integer nullableValue = null; // Works
Type Conversion:
- Wrapper classes allow easy conversion between types.
Integer i = 10; double d = i.doubleValue(); // Convert Integer to double

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Integer i = 10;
double d = i.doubleValue(); // Convert Integer to double
Immutability:
- Wrapper objects are immutable, ensuring safety in multi-threaded environments.

Key Features:

Autoboxing and Unboxing:
- Autoboxing automatically converts primitives to their wrapper objects.
- Unboxing automatically converts wrapper objects back to primitives.
Integer obj = 10; // Autoboxing int primitive = obj; // Unboxing

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Integer obj = 10; // Autoboxing
int primitive = obj; // Unboxing
String Parsing:
- Converting strings to numbers or vice versa is simplified.
int num = Integer.parseInt("42"); // String to int String str = Integer.toString(42); // int to String

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int num = Integer.parseInt("42"); // String to int
String str = Integer.toString(42); // int to String

Example Code:

public class WrapperExample {
    public static void main(String[] args) {
        // Autoboxing
        Integer num = 5; // int to Integer
        System.out.println("Wrapper Object: " + num);

        // Unboxing
        int primitive = num; // Integer to int
        System.out.println("Primitive Value: " + primitive);

        // Utility method: Parsing a String
        String str = "123";
        int parsedNum = Integer.parseInt(str);
        System.out.println("Parsed Number: " + parsedNum);

        // Storing primitive types in a collection
        List&lt;Double&gt; doubles = new ArrayList&lt;&gt;();
        doubles.add(3.14); // Autoboxing
        doubles.add(2.71);
        System.out.println("List of Doubles: " + doubles);
    }
}

public class WrapperExample {

public static void main(String[] args) {

// Autoboxing

Integer num = 5; // int to Integer

System.out.println("Wrapper Object: " + num);

// Unboxing

int primitive = num; // Integer to int

System.out.println("Primitive Value: " + primitive);

// Utility method: Parsing a String

String str = "123";

int parsedNum = Integer.parseInt(str);

System.out.println("Parsed Number: " + parsedNum);

// Storing primitive types in a collection

List<Double> doubles = new ArrayList<>();

doubles.add(3.14); // Autoboxing

doubles.add(2.71);

System.out.println("List of Doubles: " + doubles);

}

Conclusion:

Wrapper classes bridge the gap between primitives and objects in Java. They are essential for working with frameworks, collections, and generics that require objects. They also provide additional utility methods for parsing, type conversion, and more.

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