Wrapper classes in Java provide object representations of primitive data types. They are useful when working with Java features that require objects, such as collections and generics.
- Each wrapper class encapsulates a corresponding primitive value inside an object (e.g., Integer for int, Double for double).
- Java provides wrapper classes for all eight primitive data types to support object-based operations.
Example: Converting Primitive to Wrapper (Autoboxing)
Java
class Geeks {
public static void main(String[] args) {
int b = 357;
// Autoboxing: primitive int -> Integer object
Integer a = b;
System.out.println("The primitive int b is: " + b);
System.out.println("The Integer object a is: " + a);
}
}
OutputThe primitive int b is: 357
The Integer object a is: 357
Explanation: Here, the primitive int value is automatically converted into an Integer object by Java. This automatic conversion is called autoboxing.
Need Of Wrapper Classes
Wrapper classes are required in Java for the following reasons:
- Java collections (ArrayList, HashMap, etc.) store only objects, not primitives.
- Wrapper objects allow primitives to be used in object-oriented features like methods, synchronization, and serialization.
- Objects support null values, while primitives do not.
- Wrapper classes provide utility methods such as compareTo(), equals(), and toString().
Autoboxing and Unboxing
1. Autoboxing
The automatic conversion of primitive types to the object of their corresponding wrapper classes is known as autoboxing. For example: conversion of int to Integer, long to Long, double to Double, etc.
Java
import java.util.ArrayList;
class Geeks {
public static void main(String[] args) {
char ch = 'a';
// Autoboxing: char -> Character
Character c = ch;
ArrayList<Integer> list = new ArrayList<>();
// Autoboxing: int -> Integer
list.add(25);
System.out.println(list.get(0));
}
}
2. Unboxing
Unboxing is the automatic conversion of a wrapper class object back into its corresponding primitive type.
Java
import java.util.ArrayList;
class Geeks {
public static void main(String[] args) {
Character ch = 'a';
// Unboxing: Character -> char
char c = ch;
ArrayList<Integer> list = new ArrayList<>();
list.add(24);
// Unboxing: Integer -> int
int num = list.get(0);
System.out.println(num);
}
}
Java Wrapper Classes Example
Java
class Geeks {
public static void main(String[] args) {
byte b = 1;
Byte byteObj = Byte.valueOf(b);
int i = 10;
Integer intObj = Integer.valueOf(i);
float f = 18.6f;
Float floatObj = Float.valueOf(f);
double d = 250.5;
Double doubleObj = Double.valueOf(d);
char c = 'a';
Character charObj = c; // autoboxing
System.out.println("Wrapper Objects:");
System.out.println(byteObj);
System.out.println(intObj);
System.out.println(floatObj);
System.out.println(doubleObj);
System.out.println(charObj);
// Unboxing
byte bv = byteObj;
int iv = intObj;
float fv = floatObj;
double dv = doubleObj;
char cv = charObj;
System.out.println("\nUnwrapped values:");
System.out.println(bv);
System.out.println(iv);
System.out.println(fv);
System.out.println(dv);
System.out.println(cv);
}
}
