Wrapper Classes in Java

Wrapper classes convert primitive data types into objects.

Primitive to Wrapper Mapping

• int → Integer
• char → Character
• double → Double
• boolean → Boolean

Why Wrapper Classes Are Needed

• Collections store objects only
• Useful in frameworks
• Supports utility methods
• Required for generics

Real-World Example

ArrayList cannot directly store primitive int values, so Integer objects are used.

import java.util.*;

public class Main {
    public static void main(String[] args) {
        ArrayList<Integer> list = new ArrayList<>();

        list.add(10);
        list.add(20);

        System.out.println(list);
    }
}

Autoboxing

Automatic conversion of primitive to wrapper object.

Integer x = 100;

Unboxing

Automatic conversion of wrapper object to primitive.

int y = x;

Useful Methods

• Integer.parseInt()
• Double.parseDouble()
• Boolean.valueOf()
• Character.isDigit()

Interview Questions

• Why are wrapper classes required?
• What is autoboxing?
• Difference between int and Integer?
• Why collections cannot store primitive types?