Java Static Keywords

5 Key excerpts on "Java Static Keywords"

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  eBook - ePub

  Getting Skilled with Java

  Learn Java Programming from Scratch with Realistic Applications and Problem Solving Programmes (English Edition)

  • M Rashid Raza(Author)
  • 2022(Publication Date)
  • BPB Publications

    (Publisher)

  Class variables are those variables, which are declared at the class level and all the instances of that class are going to share the same variable with the same value. If any instance updates the value of a class variable, the same will be updated for all the instances of that class. It is not a good practice to update the value of any class variable by any program. The variables that have a fixed value should be declared as class variables. We declare the class variable using a static keyword. The static keyword ensures that only one instance of this variable will be created. The class variable is also known as static variable. Below is an example of variable declaration and assignation.

  static int age = 5;

  If you don’t assign any value in a static variable and further use that variable to perform some operation in your program, then it will give you the default value of that variable based on specified default values for that data type.

  Example 3.4 : Default value assignation by JVM

  For example: public class StaticVariable { static int age; public static void main(String[] args) { System.out.println(age); } }

  The preceding program will run successfully and print 0, which is the default value for int in Java.

  NOTE: Anything declared using static keyword gets loaded in the memory at the time the class gets loaded. Static is not dependent on object initialization. Hence, class variable is always declared as a static.

  Constant variable

  Constant variables are those variables that are fixed and once you assign a value to it, you cannot change it. It will remain the same always. If you try to reassign or update the value of the final variable, the compiler will generate an error message for you “The final field FinalVariable.XYZ cannot be assigned

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  eBook - ePub

  Java Professional Interview Guide

  Learn About Java Interview Questions and Practise Answering About Concurrency, JDBC, Exception Handling, Spring, and Hibernate

  • Mandar Maheshwar Jog(Author)
  • 2021(Publication Date)
  • BPB Publications

    (Publisher)

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Can I apply static anywhere apart from variables?

Certainly, apart from the variables, you can apply the static keyword at numerous locations. You can make any method as static. You can declare the static block, which executes before the main() method. Apart from this, there is a concept called as static instantiation block, which is executed just before the creation of an object. You can also use the static keyword with a class that is termed as a static class. But, you cannot make any class as static unless it is nested in some other class. Such class is called as a static nested inner class .

What is the use of this keyword?

The this keyword refers the current object. Normally, it is used to call another constructor of the same object. This is the only way to call the constructor of the same object. You can call a parameterized constructor from default or from default to a parameterized constructor using the this keyword.
Also, if there is any ambiguity with the local variables and instance variables, you can use the this keyword to denote the instance variables differently than the local variable.

Explain the significance of the super keyword

The super keyword refers to the super class. If you want to call the members of the super class explicitly from a subclass, then you can use this keyword. You can invoke data members or member functions of a super class. Not only that, you can also invoke the constructor of the super class explicitly from a subclass constructor.
Another use of the super keyword is done by JVM when it calls the default constructor of super class implicitly from the constructor of the subclass. The super keyword must be the first line of the constructor.

Why the super keyword must be located as the first line of the constructor?

When we say that we are in a subclass, it obviously contains some data members. Many times, the data members of the subclass are dependent on the data members of the super class. So, unless the data members of super classes are initialized, the subclass data members cannot be initialized. So, to make sure that the super class data members are initialized prior to any member of the subclass, the super keyword is placed as the first line of the constructor.