What is the difference between an instance member of a class and a static member of a class?

An instance member belongs to a specific object of the class, while a static member belongs to the class itself.

Main differences:

• Access:
  • Instance members are accessed through an object of the class: ClassName object = new ClassName(); object.instanceVariable; object.instanceMethod();
  • Static members are accessed through the class name or through an object: ClassName.staticVariable; ClassName.staticMethod(); object.staticVariable; object.staticMethod(); (Accessing through an object is not recommended).
• Lifetime:
  • Instance members are created when each object of the class is created and destroyed when the object is no longer accessible (garbage collection).
  • Static members are created when the class is loaded into JVM memory and exist until the class is unloaded.
• Memory:
  • Each object of the class has its own copy of instance members, stored in the object's memory.
  • There is only one copy of each static member, shared among all objects of the class.
• Keyword:
  • Instance members do not use the static keyword.
  • Static members use the static keyword.
• Access from other members:
  • Static methods cannot directly access instance members without creating an object.
  • Instance methods can access both instance and static members.

Example:

class Example {
    int instanceVariable; // Instance member
    static int staticVariable = 0; // Static member

    // Instance method
    void instanceMethod() {
        System.out.println("Instance variable: " + this.instanceVariable);
        System.out.println("Static variable from instance method: " + staticVariable);
    }

    // Static method
    static void staticMethod() {
        System.out.println("Static variable from static method: " + staticVariable);
        // System.out.println("Instance variable from static method: " + instanceVariable); // Compilation error
    }
}