Let's look at static variables and static methods first.
What is Static Variable in Java?
Static variable in Java is variable which belongs to the class and initialized only once at the start of the execution. It is a variable which belongs to the class and not to object(instance ). Static variables are initialized only once, at the start of the execution. These variables will be initialized first, before the initialization of any instance variables.
A single copy to be shared by all instances of the class
A static variable can be accessed directly by the class name and doesn’t need any object
Syntax :
<class-name>.<variable-name>
What is Static Method in Java?
Static method in Java is a method which belongs to the class and not to the object. A static method can access only static data. It is a method which belongs to the class and not to the object(instance). A static method can access only static data. It cannot access non-static data (instance variables).
A static method can call only other static methods and can not call a non-static method from it.
A static method can be accessed directly by the class name and doesn’t need any object
A static method cannot refer to "this" or "super" keywords in anyway
Syntax :
<class-name>.<method-name>
Note: main method is static, since it must be accessible for an application to run, before any instantiation takes place.
Lets learn the nuances of the static keywords by doing some excercises!
Example: How to call static variables & methods
Step 1) Copy the following code into a editor
public class Demo{
public static void main(String args[]){
Student s1 = new Student();
s1.showData();
Student s2 = new Student();
s2.showData();
//Student.b++;
//s1.showData();
}
}
class Student {
int a; //initialized to zero
static int b; //initialized to zero only when class is loaded not for each object created.
Student(){
//Constructor incrementing static variable b
b++;
}
public void showData(){
System.out.println("Value of a = "+a);
System.out.println("Value of b = "+b);
}
//public static void increment(){
//a++;
//}
}
Step 2) Save & Compile the code. Run the code as, java Demo.
Step 3) Expected output show below Following diagram shows, how reference variables & objects are created and static variables are accessed by the different instances.
What is Static Block in Java?
The static block is a block of statement inside a Java class that will be executed when a class is first loaded into the JVM. A static block helps to initialize the static data members, just like constructors help to initialize instance members.
class Test{
static {
//Code goes here
}
}
Following program is the example of java static block.
Example: How to access static block
public class Demo {
static int a;
static int b;
static {
a = 10;
b = 20;
}
public static void main(String args[]) {
System.out.println("Value of a = " + a);
System.out.println("Value of b = " + b);
}
}
