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What is difference between protected static method and protected method? For example demo and demo2 in Data2 respectively

Data.java:

package pack1;

import pack2.*;

public class Data extends Data2 {

    public static void main(String args[]){
        System.out.println("From main class");
        Data d=new Data();
        d.first(); 
    }

    void first(){
        Data2 d2=new Data2();

        d2.demo();
        d2.demo2();
    }
}

Data2.java:

package pack2;

public class Data2 {
    protected static void demo(){
        System.out.println("In method demo");
    }

    protected void demo2(){
        System.out.println("In method demo2");
    }
}

closed as unclear what you're asking by gnat, GlenH7, user40980, Kilian Foth, jwenting Sep 29 '14 at 11:19

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  • 3
    You posted your code, but you forgot to ask a question. – Philipp Feb 17 '14 at 10:09
5

A static method is a method which doesn't belong to a particular instance of a class. It belongs to the class itself.

You could write Demo2.demo() to call the static method directly on the class without creating an instance. But you couldn't call Demo2.demo2() because demo2 isn't static and thus can only be called on an instance you created with the new keyword.

Because a static method is not (necessarily) bound to a specific instance of a class, it can only access static variables (the value of static variables is shared between all instances of a class while the value of a non-static variable is different for each instance you create with the new keyword).

You might wonder "what's the reason for a static protected method, considering that it's impossible to call it from anywhere except from an instance of that class?". Usually there isn't much reason to declare a private or protected method as static. Static methods are usually public. But when the behavior of a method does not affect or is affected by the state of the current instance, declaring it static can be a way to document this fact.

  • +1 for mentioning that code artifacts can be a form of documentation and not necessarily functionality. – Brandon Feb 17 '14 at 15:23
  • So how would you call a static protected method from an imported api or jar – ford prefect Oct 23 '14 at 15:21
  • 1
    You said: "it's impossible to call it from anywhere except from an instance of that class" but that's not exactly right since it can be called by other classes in the same package. In which case package visibility may be more appropriate. – regjo Jan 21 '16 at 14:35

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