Java
Wrapper Classes in Java: Concept and Usage
Introduction to Wrapper Classes in Java
Java provides wrapper classes to convert primitive data types into objects. These classes are part of the java.lang package and offer various utility methods for type conversion, data manipulation, and object-oriented programming.
What Are Wrapper Classes in Java?
Wrapper classes in Java are used to encapsulate primitive data types within objects. Each primitive type has a corresponding wrapper class:
| Primitive Type | Wrapper Class |
| byte | Byte |
| short | Short |
| int | Integer |
| long | Long |
| float | Float |
| double | Double |
| char | Character |
| boolean | Boolean |
Importance of Wrapper Classes
- Object Representation: Converts primitive types into objects.
- Collection Framework Support: Used in Java Collections like ArrayList and HashMap.
- Utility Methods: Provides methods for parsing, conversion, and comparisons.
- Null Handling: Unlike primitive types, wrapper classes can store null values.
Java Primitive to Object Conversion
Using Wrapper Class Constructors (Deprecated in Java 9)
Before Java 9, wrapper classes had constructors to convert primitives into objects:
Integer obj = new Integer(10); // Deprecated
Using valueOf() Method
Instead of constructors, Java recommends using valueOf() for object creation:
Integer obj = Integer.valueOf(10);
Java Wrapper Class Methods
Wrapper classes provide several utility methods for type conversion and manipulation.
Commonly Used Methods
| Method | Description |
|---|---|
| parseInt(String s) | Converts a string to an int |
| valueOf(String s) | Converts a string to an object |
| toString() | Converts an object to a string |
| doubleValue() | Returns the double equivalent |
| intValue() | Returns the integer equivalent |
| compareTo(T obj) | Compares two objects |
Example:
String number = "100"; int result = Integer.parseInt(number); System.out.println(result); // Output: 100
Autoboxing and Unboxing in Java
What is Autoboxing in Java?
Autoboxing is the automatic conversion of a primitive type into its corresponding wrapper class.
int num = 50; Integer obj = num; // Autoboxing
What is Unboxing in Java?
Unboxing is the reverse process, where an object is converted back to a primitive type.
Integer obj = 100; int num = obj; // Unboxing
Why is Autoboxing and Unboxing Important?
- Reduces Boilerplate Code: No need for explicit conversion.
- Seamless Integration with Collections: Java collections work with objects, not primitives.
- Enhances Readability: Cleaner and more intuitive code.
Performance Considerations of Wrapper Classes
- Memory Overhead: Wrapper objects take more space than primitives.
- Garbage Collection: Frequent boxing/unboxing can impact performance.
