static is a non-access modifier in Java which is applicable for the following:
- blocks
- variables
- methods
- nested classes
To create a static member(block,variable,method,nested class), precede its declaration with the keyword static. When a member is declared static, it can be accessed before any objects of its class are created, and without reference to any object. For example, in below java program, we are accessing static method m1() without creating any object of Test class.
// Java program to demonstrate that a static member // can be accessed before instantiating a class class Test { // static method static void m1() { System.out.println("from m1"); } public static void main(String[] args) { // calling m1 without creating // any object of class Test m1(); } } |
Output:
from m1
Static blocks
If you need to do computation in order to initialize your static variables, you can declare a static block that gets executed exactly once, when the class is first loaded. Consider the following java program demonstrating use of static blocks.
// Java program to demonstrate use of static blocks class Test { // static variable static int a = 10; static int b; // static block static { System.out.println("Static block initialized."); b = a * 4; } public static void main(String[] args) { System.out.println("from main"); System.out.println("Value of a : "+a); System.out.println("Value of b : "+b); } } |
Output:
Static block initialized. from main Value of a : 10 Value of b : 40
For Detailed article on static blocks, see static blocks
Static variables
When a variable is declared as static, then a single copy of variable is created and shared among all objects at class level. Static variables are, essentially, global variables. All instances of the class share the same static variable.
Important points for static variables :-
- We can create static variables at class-level only. See here
- static block and static variables are executed in order they are present in a program.
Below is the java program to demonstrate that static block and static variables are executed in order they are present in a program.
// java program to demonstrate execution // of static blocks and variables class Test { // static variable static int a = m1(); // static block static { System.out.println("Inside static block"); } // static method static int m1() { System.out.println("from m1"); return 20; } // static method(main !!) public static void main(String[] args) { System.out.println("Value of a : "+a); System.out.println("from main"); } } |
Output:
from m1 Inside static block Value of a : 20 from main
Static methods
When a method is declared with static keyword, it is known as static method. The most common example of a static method is main( ) method.As discussed above, Any static member can be accessed before any objects of its class are created, and without reference to any object.Methods declared as static have several restrictions:
- They can only directly call other static methods.
- They can only directly access static data.
- They cannot refer to this or super in any way.
Below is the java program to demonstrate restrictions on static methods.
// java program to demonstrate restriction on static methods class Test { // static variable static int a = 10; // instance variable int b = 20; // static method static void m1() { a = 20; System.out.println("from m1"); // Cannot make a static reference to the non-static field b b = 10; // compilation error // Cannot make a static reference to the // non-static method m2() from the type Test m2(); // compilation error // Cannot use super in a static context System.out.println(super.a); // compiler error } // instance method void m2() { System.out.println("from m2"); } public static void main(String[] args) { // main method } } |
When to use static variables and methods?
Use the static variable for the property that is common to all objects. For example, in class Student, all students shares the same college name. Use static methods for changing static variables.
Consider the following java program, that illustrate the use of static keyword with variables and methods.
// A java program to demonstrate use of // static keyword with methods and variables // Student class class Student { String name; int rollNo; // static variable static String cllgName; // static counter to set unique roll no static int counter = 0; public Student(String name) { this.name = name; this.rollNo = setRollNo(); } // getting unique rollNo // through static variable(counter) static int setRollNo() { counter++; return counter; } // static method static void setCllg(String name){ cllgName = name ; } // instance method void getStudentInfo(){ System.out.println("name : " + this.name); System.out.println("rollNo : " + this.rollNo); // accessing static variable System.out.println("cllgName : " + cllgName); } } //Driver class public class StaticDemo { public static void main(String[] args) { // calling static method // without instantiating Student class Student.setCllg("XYZ"); Student s1 = new Student("Alice"); Student s2 = new Student("Bob"); s1.getStudentInfo(); s2.getStudentInfo(); } } |
Output:
name : Alice rollNo : 1 cllgName : XYZ name : Bob rollNo : 2 cllgName : XYZ
Static nested classes : We can not declare top-level class with a static modifier, but can declare nested classes as static. Such type of classes are called Nested static classes. For static nested class, see static nested class in java
This article is contributed by Gaurav Miglani. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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