What is null in Java?

There is also a special null type, the type of the expression null, which has no name. Because the null type has no name, it is impossible to declare a variable of the null type or to cast to the null type. The null reference is the only possible value of an expression of null type. The null reference can always be cast to any reference type. In practice, the programmer can ignore the null type and just pretend that null is merely a special literal that can be of any reference type.

Autoboxing and Unboxing

Review Wish list:
built in types >> primitive data type
hexadecimal and octal numbers
stacks and cues
operators >> assignment
escape sequences: \n \” \
boolean algebra
STATIC (everything)
try catch exceptions (throwing exceptions)
INHERITANCE
POLYMORPHISM
type compatibility (down casting abstract classes)
Wrapper class
syntax for arrays vs array list
2d array syntax
tracing recursive methods
SORTS >> selection, insertion, merge, quick
SEARCHES >> binary, sequential
Big O Notation