Declarations and Access Control (Part III)

Other Modifiers—Members :

• final methods cannot be overridden in a subclass.
• abstract methods are declared, with a signature, a return type, and an optional throws clause, but are not implemented.
• The synchronized modifier applies only to methods and code blocks.
• synchronized methods can have any access control and can also be marked final.
• The native modifier applies only to methods.
• The strictfp modifier applies only to classes and methods.

Methods with var-args :

• As of Java 5, methods can declare a parameter that accepts from zero to many arguments, a so-called var-arg method.
• A var-arg parameter is declared with the syntax type... name; for instance : doStuff(int... x) { }.
• A var-arg method can have only one var-arg parameter.
• In methods with normal parameters and a var-arg, the var-arg must come last.

Variable Declarations :

• Instance variables can have any access control and be marked final or transient.
• Instance variables can't be abstract, synchronized, native, or strictfp.
• It is legal to declare a local variable with the same name as an instance variable; this is called "shadowing."
• final variables cannot be reinitialized once assigned a value.
• final reference variables cannot refer to a different object once the object has been assigned to the final variable.
• final reference variables must be initialized before the constructor completes.
• There is no such thing as a final object. An object reference marked final does not mean the object itself is immutable.
• The transient modifier applies only to instance variables.
• The volatile modifier applies only to instance variables.

Array Declarations :

• Arrays can hold primitives or objects, but the array itself is always an object.
• When you declare an array, the brackets can be to the left or right of the variable name.
• It is never legal to include the size of an array in the declaration.

Static Variables and Methods :

• They are not tied to any particular instance of a class.
• No classes instances are needed in order to use static members of the class.
• There is only one copy of a static variable / class and all instances share it.
• static methods do not have direct access to non-static members.

Enums :

• An enum specifies a list of constant values that can be assigned to a particular type.
• An enum can be declared outside or inside a class, but NOT in a method.
• An enum declared outside a class must NOT be marked static, final, abstract, protected, or private.
• enum constructors can NEVER be invoked directly in code. They are always called automatically when an enum is initialized.
• The semicolon at the end of an enum declaration is optional.