what is difference between declaring variable out of main method and inside main method?

Question

When I was reading book about Java , I saw one example written like this. And I am wondering can I declare variable in outside of main method ? What is difference between declaring variable outside and inside main method? what is " static" 's role in here ? Please some one explain to me? I am new in java.

public class Printstuff {
      static int an_integer = 0;
        public static void main(String[] args) {
          int an_integer = 2;
          String[] some_strings = {"Shoes", "Suit", "Tie" };
          an_integer = an_integer - 1;
          some_strings[an_integer] = some_strings[an_integer] +"+++";
          for (int i = 0; i < some_strings.length; i++)
            System.out.println(some_strings[Printstuff.an_integer]);
        }
    }

Best regards.

Answer 1

Declaring a variable in the main method will make it available only in the main. Declaring a variable outside will make it available to all the methods of the class, including the main method.

Example :

public class Foo {
   private String varOne = "Test";

   public void testOne() {
     System.out.println(varOne);
     System.out.println(varTwo); // Error, this variable is available in the testTwo method only
   }

   public void testTwo() {
     String varTwo = "Bar";
     System.out.println(varOne); // Will display "Test"
     System.out.println(varTwo); // Will display "Bar"
   }
}

Answer 2

1) Inside vs Outside:

If you declare your object inside a method, it will be visible only in this method. Basically, if you put brackets around it, it's only visible/accessible from within these brackets.

If you declare your object outside the method (inside the class), it depends on the access modifier.
By default, it's visible/accessible from within that class and the whole package.

2) Static

Static means, that static methods / variables belongs to the class itself, and not to its objects (instances of that class).

Example:

public class Members {

  static int memberCount;

  public Members() {
     memberCount++;
  }
}

memberCount exists only once, no matter how many Objects of the class exists. (even before any object is created!)

Every time you create a new Object of Members, memberCount is increased. Now you can access it like this: Members.memberCount