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Is it bad practice to, in the class which contains the main method, declare all members of that class as static? If so, why? Is it better to, in the main method, create a new instance of the enclosing class, and run the program from the constructor so to speak?

EDIT: (clarification) I know the concept about static and singletons and generally when to use it. But this question regards specifically the main-class of a program. @Andrew Tobilko (who apparently removed his answer..) seems to have best understood my question judging from his answer. In my case, my main-class is about 200 LOC, and it uses two other small class (< 100 LOC each), so it's a small program. The main-class contains creating a Swing GUI and some running logic, nothing which there needs to be several instances of, so I thought I might just make everything static, to be able to use everything from the static main-method. Is this motivated? A friend who codes in C# told me using a lot of static would mean death penalty in C#. Can there be some memory problems with it or something?

Jonathan Andersson
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    It depends on what you are doing... –  Nov 19 '15 at 19:16
  • Why not create separate classes for functionality - and instantiate objects from the main as required? – TR1 Nov 19 '15 at 19:16
  • `static` access modifier is used for class instances. If you require a single instance of that member, then you could assign it as static. It is on the requirement – Rohit Batta Nov 19 '15 at 19:17
  • the only draw back of making everything static is that variables will have the same value across all instances of the class. – Paul Nov 19 '15 at 19:17
  • Do you need multiple instances? There's your answer. – Sam McCreery Nov 19 '15 at 19:18

4 Answers4

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It's not 'better' - it depends on what you need to do. Declaring all the members of a class as static (including methods) simply turns the class into a singleton. If that's your use-case, then yes.

Declaring an attribute as static means that there is only one copy of this attribute which is shared by all the instances of the class.

If your use-case requires creating multiple instances, and each one of these objects should have its own "private copy" of an attribute then you shouldn't declare that attribute as static.

It's recommended to read more about the topic before you continue implementing.

Nir Alfasi
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Static Variables:

The static key word is used to create variables that will exist independently of any instances created for the class. Only one copy of the static variable exists regardless of the number of instances of the class.

Static variables are also known as class variables. Local variables cannot be declared static.

Static Methods:

The static key word is used to create methods that will exist independently of any instances created for the class.

Static methods do not use any instance variables of any object of the class they are defined in. Static methods take all the data from parameters and compute something from those parameters, with no reference to variables.

Class variables and methods can be accessed using the class name followed by a dot and the name of the variable or method. static modifier are for class members. It should be only used when you want to get a single copy of instance through out the program.

Below is example to explain it, 

public class InstanceCounter {

   private static int numInstances = 0;

   protected static int getCount() {
      return numInstances;
   }

   private static void addInstance() {
      numInstances++;
   }

   InstanceCounter() {
      InstanceCounter.addInstance(); 
   }

   public static void main(String[] arguments) {
      System.out.println("Starting with " +
      InstanceCounter.getCount() + " instances");
      for (int i = 0; i < 500; ++i){
         new InstanceCounter();
      }
      System.out.println("Created " +
      InstanceCounter.getCount() + " instances");
   }
}

This would produce the following result:

Started with 0 instances
Created 500 instances

You could check this DuplicateQuestion for your reference

Community
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Rohit Batta
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Static entity can give a call to or interact with static entities i.e. a static method can call only a static method or interact with a static variable. That is the property of static methods. Main class in java is mostly declared as "public static void main", which makes main a static method. Hence, the functions it calls are to be static.

Rubal
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  • Generally class used for constants will hold all final static variables.
  • Utility classes holds all static methods.Eg - Math class in Java
bkakran
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