Question

Explain how class (static) variables and methods differ from their instance counterparts. Give an example of a class that contains at least one class variable and at least one class method. Explain why using a class variable and method rather than an instance variable and method would be the correct choice in the example you select.

Answer 1

Static Variables and methods are part of heap memory. The static variables and methods can be accessed by the objects and can be accessed without even creating an object.

In order to use any instance variables or methods, you must create an object. It is impossible to use an instance variable or call an instance method without creating a method.

But, static variables or methods are not like that. You can call those either using an object and without even creating an object. It plays a very important role in different scenarios.

Let me explain it with an example:
public class Student{

public static void main(String []args){
// There are 10 student objects are being created.
Student obj[] = new Student[10] ;
for(int i = 0; i < 10; i++) {
obj[i].getMarks();
obj[i].display();
}
}
}

If you see the example, I created an array of 10 student objects. We need to display college code which is common for all the students. If we do not have a static variable, you need to allocate 10 memory space for 10 student objects. If we have 1000 objects then 1000 memory space. This problem can be avoided by using a static variable college code which can be accessed by all the objects.

public class Student{

public static void main(String []args){
// There are 10 student objects are being created.
Student obj[] = new Student[10] ;
// static
static int collegeCode = "123";
for(int i = 0; i < 10; i++) {
obj[i].getMarks();
obj[i].display();
}
System.out.println("Hello World");
}
}

Similary, the static method would be useful, if you want to display some generic information. You don't need to create an object for the same.

Please do comment for any doubts or modifications!