java basics static method

Question

can a static method be invoked before even a single instances of the class is constructed?

• Brian: When learning java, one of your first encounters with static concepts is the use of System.out.println(). It is an interesting bit of code, in particular System and System.out; let alone the implementations of println().

Answer 1

absolutely, this is the purpose of static methods:

class ClassName {
 public static void staticMethod() {
 }
}

In order to invoke a static method you must import the class:

import ClassName;
// ...
ClassName.staticMethod();

or using static imports (Java 5 or above):

import static ClassName.staticMethod;
// ...
staticMethod();

Answer 2

As others have already suggested, it is definitely possible to call a static method on a class without (previously) creating an instance--this is how Singletons work. For example:

import java.util.Calendar;
public class MyClass 
{
 // the static method Calendar.getInstance() is used to create 
 // [Calendar]s--note that [Calendar]'s constructor is private
 private Calendar now = Calendar.getInstance();
}

If you mean, "is it possible to automatically call a specific static method before the first object is initialized?", see below:

public class MyClass
{
 // the static block is garanteed to be executed before the
 // first [MyClass] object is created.
 static {
 MyClass.init();
 }
 private static void init() {
 // do something ...
 }
}

Answer 3

Yes, that is exactly what static methods are for.

ClassName.staticMethodName();

Answer 4

Yes, because static methods cannot access instance variables, so all the JVM has to do is run the code.

Answer 5

Static methods are meant to be called without instantiating the class.

Answer 6

Yes, you can access it by writing ClassName.methodName before creating any instance.

Answer 7

Not only can you do that, but you should do it.

Answer 8

In fact, there are a lot of "utility classes", like Math, Collections, Arrays, and System, which are classes that cannot be instantiated, but whose whole purpose is to provide static methods for people to use.

Answer 9

Yes, that's definitely possible. For example, consider the following example...

class test {
 public static void main(String arg[]) {
 System.out.println("hello");
 }
 }

...if then we run it, it does execute, we never created a instance of the class test. In short, the statement public static void main(String arg[]) means execute the main method without instantiating the class test.