Example
The static keyword is used on a class, method, or field to make them work independently of any instance of the class.
- Static fields are common to all instances of a class. They do not need an instance to access them.
- Static methods can be run without an instance of the class they are in. However, they can only access static fields of that class.
- Static classes can be declared inside of other classes. They do not need an instance of the class they are in to be instantiated.
public class TestStatic
{
static int staticVariable;
static {
// This block of code is run when the class first loads
staticVariable = 11;
}
int nonStaticVariable = 5;
static void doSomething() {
// We can access static variables from static methods
staticVariable = 10;
}
void add() {
// We can access both static and non-static variables from non-static methods
nonStaticVariable += staticVariable;
}
static class StaticInnerClass {
int number;
public StaticInnerClass(int _number) {
number = _number;
}
void doSomething() {
// We can access number and staticVariable, but not nonStaticVariable
number += staticVariable;
}
int getNumber() {
return number;
}
}
}
// Static fields and methods
TestStatic object1 = new TestStatic();
System.out.println(object1.staticVariable); // 11
System.out.println(TestStatic.staticVariable); // 11
TestStatic.doSomething();
TestStatic object2 = new TestStatic();
System.out.println(object1.staticVariable); // 10
System.out.println(object2.staticVariable); // 10
System.out.println(TestStatic.staticVariable); // 10
object1.add();
System.out.println(object1.nonStaticVariable); // 15
System.out.println(object2.nonStaticVariable); // 10
// Static inner classes
StaticInnerClass object3 = new TestStatic.StaticInnerClass(100);
StaticInnerClass object4 = new TestStatic.StaticInnerClass(200);
System.out.println(object3.getNumber()); // 100
System.out.println(object4.getNumber()); // 200
object3.doSomething();
System.out.println(object3.getNumber()); // 110
System.out.println(object4.getNumber()); // 200
