What are wrappers (Wrapper classes) in Java?

Wrapper classes in Java are special classes that represent reference data types for primitive types. They allow working with primitives as objects.

Main features and purposes:

• Objects for primitives: Each primitive type (byte, short, int, long, float, double, boolean, char) has a corresponding wrapper class (Byte, Short, Integer, Long, Float, Double, Boolean, Character).
• Inheritance from Object: All wrapper classes are descendants of the Object class, which allows their use in collections (such as ArrayList, HashMap, HashSet) and other APIs that work with objects.
• Fields and methods: Wrapper classes contain useful methods for working with the corresponding primitive values (e.g., string parsing, comparison). They also contain constants (e.g., Integer.MAX_VALUE, Integer.MIN_VALUE).
• Autoboxing and unboxing: Java mechanisms that automatically convert between primitive types and their wrappers.

  // Autoboxing
  Integer numObject = 10; // primitive int is automatically boxed into Integer
  
  // Unboxing
  int numPrimitive = numObject; // Integer object is automatically unboxed into primitive int
  

• Immutability: Wrapper class objects are immutable. Their value cannot be changed after creation.

  Integer a = 5;
  Integer b = a; // b references the same object
  a = 10; // a now references a new object with value 10, the object with 5 remains
  

Applications:

• Working with Java collections.
• Using in Stream API.
• Nullable values (the wrapper object can be null, primitive — no).
• Helper methods for type conversion and constants.
• In generics, which cannot work directly with primitive types.