Static member variables
or class variables belong to the class. Unlike instance variable values, each
object does not get its own unique value. A class variable belong to the class
and sense there is only one class there is only one copy. When writing a class
variable you must add the key word static. Later when accessing that class
variable, you must use the (class_name. variable_name.)
A static method also uses
the key word (static method_name.) You can access a static method by using the (class_name.method_name.)
Static methods can access static variables in the class, but they can’t access
instance variables.
A static method can be
used if you have a method that doesn’t deal with instance data of the class.
Another typical use of static method is when you access a constants. We can
make or own constant variable by using the key words final and static. When
making a constant variable you must set its value in the class, and it will
remain constant. This mean you cannot reassign that variable later on. Below
shows examples of static variables, static methods, and constants.
class Thing {
public String name;
public static String description;
public final static int LUCKY_NUMBER = 7;
public static int count = 0;
public int id;
public Thing(){
id = count;
count++;
}
public void showName(){
System.out.println("object
id; " + id + description + ":" + name);
}
public static void showInfo(){
System.out.println(description);
}
}
public class App {
public static void main(String[] args) {
Thing.description = "I am a
thing";
Thing.showInfo();
System.out.println("Before
creating objects, count is: " + Thing.count);
Thing
thing1 = new Thing();
Thing
thing2 = new Thing();
System.out.println("After
creating objects, count is: " + Thing.count);
thing1.name = "bob";
thing2.name = "sue";
thing1.showName();
thing2.showName();
System.out.println(Math.PI);
System.out.println(Thing.LUCKY_NUMBER);
}
}
