Java Tutorials
Java ArrayList: How to Use, ArrayList Methods & Examples
What is ArrayList in Java? ArrayList in Java is a data structure that can be stretched to...
The static can be:
Let's look at static variables and static methods first.
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.
Syntax :
<class-name>.<variable-name>
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).
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.
Step 4) It is possible to access a static variable from outside the class using the syntax ClassName.Variable_Name. Uncomment line # 7 & 8 . Save , Compile & Run . Observe the output.
Value of a = 0 Value of b = 1 Value of a = 0 Value of b = 2 Value of a = 0 Value of b = 3Step 5) Uncomment line 25,26 & 27 . Save , Compile & Run.
error: non-static variable a cannot be referenced from a static context a++;
Step 6) Error = ? This is because it is not possible to access instance variable "a" from java static class method "increment".
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); } }
you will get following output of the program.
Value of a = 10 Value of b = 20
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