what happens when all methods are static in java code example

Example 1: do i have to use static methods in java main

Use a static method 
when you want to be able to access the method 
without an instance of the class

Example 2: static data and static methods in java

class JavaExample{
   private static String str = "BeginnersBook";

   //Static class
   static class MyNestedClass{
	//non-static method
	public void disp() {

	   /* If you make the str variable of outer class
	    * non-static then you will get compilation error
	    * because: a nested static class cannot access non-
	    * static members of the outer class.
	    */
	   System.out.println(str); 
	}

   }
   public static void main(String args[])
   {
       /* To create instance of nested class we didn't need the outer
	* class instance but for a regular nested class you would need 
	* to create an instance of outer class first
        */
	JavaExample.MyNestedClass obj = new JavaExample.MyNestedClass();
	obj.disp();
   }
}