What are wrapper classes in Java?

In Java, wrapper classes are classes that 'wrap' primitive data types, providing object form for primitives. For example, Integer for int, Boolean for boolean, etc.

This is useful when primitives need to be used in collections or other object-only structures.

Example:

int a = 5;
Integer wrapperA = Integer.valueOf(a); // boxing

int b = wrapperA.intValue(); // unboxing

Since Java 5, auto-boxing and auto-unboxing automatically convert between primitives and their wrappers:

Integer wrapperB = 10; // auto-boxing
int c = wrapperB;       // auto-unboxing