What's the difference between calling through and object vs class

Question

What's the difference between calling a method through an object vs a class.

for example the Class Bob

public class SecretNumber() {
    public static int secretNumber = 2;
    public static void changeSecretNumber(){
        secretNumber++;
    }
}

What would be the difference if i called it like an object

SecretNumber secretNumber = new SecretNumber();
secretNumber.changeSecretNumber();

vs calling it like this

SecretNumber.changeSecretNumber();

How would one method effect the other?

Answer 1

The result is the same.

You should call it by class name, not through the instance, because no dynamic dispatch happens.

Most compilers will give you a warning, if you do that, too. Some people argue that it should have been made a compile error.

Answer 2

In Java, unless a class method is "static", you can't call it except through an object instance.

Here's an example of a method where it would make sense to declare it "static":

• http://www.leepoint.net/notes-java/flow/methods/50static-methods.html

  public static double mean(int[] p) { int sum = 0; // sum of all the elements for (int i=0; i

http://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html

Answer 3

The second form isn't valid Java. You can only call methods on a class if they are declared static.

Answer 4

Calling a method through a class is a static method. Unless you declare the method a static method, the compiler will give you a compile error .