In the Java programming language, a keyword is one of 51 reserved words that have a predefined meaning in the language; because of this, programmers cannot use keywords as names for variables, methods, classes, or as any other identifier.

But some important keywords should known as java developer,

There are,

Final

Static

This

super

static

Synchronize

volatile

Final keyword in java

It is used to make a variable as a constant, Restrict method overriding, Restrict inheritance. It is used at variable level, method level and class level. In java language final keyword can be used in following way.

•   Final at variable level

•   Final at method level

•   Final at class level

Static keyword in java

The static keyword is used in java mainly for memory management. It is used with variables, methods, blocks and nested class. It is a keyword that are used for share the same variable or method of a given class. This is used for a constant variable or a method that is the same for every instance of a class. The main method of a class is generally labeled static.

No object needs to be created to use static variable or call static methods, just put the class name before the static variable or method to use them. Static method can not call non-static method.

In java language static keyword can be used for following

•   variable (also known as class variable)

•   method (also known as class method)

•   block

•   nested class

Difference between static and final keyword

static keyword always fixed the memory that means that will be located only once in the program where as final keyword always fixed the value that means it makes variable values constant.

Note: As for as real time statement there concern every final variable should be declared the static but there is no compulsion that every static variable declared as final.

This keyword in java

this is a reference variable that refers to the current object. It is a keyword in java language represents current class object

Usage of this keyword

•    It can be used to refer current class instance variable.

•    this() can be used to invoke current class constructor.

•    It can be used to invoke current class method (implicitly)

•    It can be passed as an argument in the method call.

•    It can be passed as argument in the constructor call.

•    It can also be used to return the current class instance.

Why use this keyword in java ?

The main purpose of using this keyword is to differentiate the formal parameter and data members of class, whenever the formal parameter and data members of the class are similar then jvm get ambiguity (no clarity between formal parameter and member of the class)

To differentiate between formal parameter and data member of the class, the data member of the class must be preceded by "this".

"this" keyword can be use in two ways.

•    this . (this dot)

•    this() (this off)

this . (this dot)

which can be used to differentiate variable of class and formal parameters of method or constructor.

"this" keyword are used for two purpose, they are

•    It always points to current class object.

•    Whenever the formal parameter and data member of the class are similar and JVM gets an ambiguity (no clarity between formal parameter and data members of the class).

Super keyword in java

Super keyword in java is a reference variable that is used to refer parent class object. Super is an implicit keyword create by JVM and supply each and every java program for performing important role in three places.

•    At variable level

•    At method level

•    At constructor level

Need of super keyword:

Whenever the derived class is inherits the base class features, there is a possibility that base class features are similar to derived class features and JVM gets an ambiguity. In order to differentiate between base class features and derived class features must be preceded by super keyword.

Synchronized Keyword in Java

Synchronized Keyword is used for when we want to allowed only one thread at a time then use Synchronized modifier. If a method or block declared as a Synchronized then at a time only one thread is allowed to operate on the given object.

Synchronized is a Modifier which is applicable for the method or block, we can not declare class or variable with this modifier.

Advantage of Synchronized

The main advantage of Synchronized keyword is we can resolve data inconsistency problem.

Dis-Advantage of Synchronized

The main dis-advantage of Synchronized keyword is it increased the waiting time of thread and effect performance of the system, Hence if there is no specific requirement it is never recommended to use synchronized keyword.

Volatile Keyword in Java

If the variable keep on changing such type of variables we have to declare with volatile modifier. Volatile is a modifier applicable only for variables but not for method and class.

If a variable declared as volatile then for every thread a separate local copy will be created. Every intermediate modification performed by that thread will takes place in local copy instead of master copy. Once the value got finalized just before terminating the thread the master copy value will be updated with local stable value.

Advantage of Volatile

The main advantage of Volatile keyword is we can resolve data inconsistency problems.

Dis-Advantage of Volatile

The main dis-advantage of Volatile keyword is, crating and maintaining a separate copy for every thread, increases complexity of the programming and effects performance of the system. Hence if there is no specific requirement it is never recommended to use volatile keyword, and it is almost outdated keyword.

Note: Volatile variable means its value keep on changing where as final variable means its value never changes. Hence final-Volatile combination is illegal combination for variables.