Static vs instance members

Inside a class definition, variables and methods can be declared either asinstance members (the default) or asstatic members (using the static keyword). Understanding how the runtime handles memory for each is critical to writing bug-free object-oriented software.

Every time you create an object using new Student(), a fresh set of instance variables is allocated on the heap. If you instantiate 100 Student objects:

• There are 100 independent copies of name and studentId in RAM.
• Mutating the name of student 1 has zero effect on student 2.
• Instance methods are invoked using an object reference: student1.getGrade().

A member marked with the static keyword belongs to the class itself rather than any individual instance:

• Single shared copy: Only one copy of a static variable exists in memory, regardless of whether you instantiate zero, one, or 10,000 objects.
• Global counters / IDs: A classic use case is an auto-incrementing ID generator:

  public class Student {
      private static int nextId = 1000; // Shared class counter
      private int id;                  // Unique per student
  
      public Student() {
          this.id = nextId++;          // Assign and increment shared counter
      }
  }

• Utility functions: Methods that perform mathematical calculations without needing object state are declared static (e.g. Math.pow(2, 8), Integer.parseInt("42")).