Java Quick Reference - Declarations and Access Control

Language Fundamentals

Operators and Assignments

Flow Control and Exceptions

Declarations and Access Control

Garbage Collection

Overloading and Overriding

Threads

The java.lang Package

The java.util Package

The java.awt Package

The java.io Package

References

Miscellaneous Notes

Tips & Traps

Mock Exams

Declarations and Access Control - Special Modifiers

Modifier	Used with	Description
abstract	Classes Interfaces Methods	Declares a Class or Method that is incomplete. All Interfaces are implicitly abstract so the modifier is redundant. A Class which has an abstract Method must be declared abstract.
final	Classes Field variables Methods Method parameters Local variables	Indicates a definition is complete and cannot be changed. Classes may not be extended. Field variables may not be modified once a value is assigned. Methods cannot be overridden. Required for Method parameters and Local variables if they are to be used by an Inner Class. Note: A Class may not be both final and abstract.
native	Methods	Indicates a platform-specific method written in another language. Note: a method cannot be both native and abstract
static	Initializers Methods Variables	Indicates an initializer, method or variable belongs to a class vs an instance (object) of the class. Static initializers are processed once, when the class is loaded. Static methods are used to access static variables. They may not be used to access non-static variables unless they specify an instance of the class.
synchronized	Methods	Indicates a method acquires a lock on an object before it executes. Used to control access to objects shared by multiple threads.
transient	Variables	Indicates the variable is not part of the permanent state of an object and may not be serialized (written to a stream).
volatile	Variables	Indicates a variable may be changed by more than one thread. Each thread has it's own copy of a working variable. Volatile ensures the variable is compared to the master copy each time it is accessed.