Object Member vs Static Member

With this class:

class ObjectMemberVsStaticMember {

    static int staticCounter = 0;
    int memberCounter = 0;

    void increment() {
        staticCounter ++;
        memberCounter++;
    }
}

the following code snippet:

final ObjectMemberVsStaticMember o1 = new ObjectMemberVsStaticMember();
final ObjectMemberVsStaticMember o2 = new ObjectMemberVsStaticMember();

o1.increment();

o2.increment();
o2.increment();

System.out.println("o1 static counter " + o1.staticCounter);
System.out.println("o1 member counter " + o1.memberCounter);
System.out.println();

System.out.println("o2 static counter " + o2.staticCounter);
System.out.println("o2 member counter " + o2.memberCounter);
System.out.println();

System.out.println("ObjectMemberVsStaticMember.staticCounter = " + ObjectMemberVsStaticMember.staticCounter);

// the following line does not compile. You need an object
// to access its members
//System.out.println("ObjectMemberVsStaticMember.staticCounter = " + ObjectMemberVsStaticMember.memberCounter);

produces this output:

o1 static counter 3
o1 member counter 1

o2 static counter 3
o2 member counter 2

ObjectMemberVsStaticMember.staticCounter = 3

Note: You should not call static members on objects, but on classes. While it does not make a difference for the JVM, human readers will appreciate it.

static members are part of the class and exists only once per class. Non-static members exist on instances, there is an independent copy for each instance. This also means that you need access to an object of that class to access its members.

Found a mistake? Have a question or improvement idea? Let me know.

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