We usually think that GC collects and removes the unreferenced objects. Instead, GC in Java tracks live objects and marks all unreferenced objects as garbage.

The heap area of the memory is where objects are allocated dynamically. We should allocate heap memory to JVM before running the application. Allocating heap to JVM in advance has a couple of consequences:

• Improves object creation rate because JVM doesn't need to communicate with the OS to get memory for each new object. Once the JVM allocates memory to an object, JVM moves the pointer toward the next available memory. 
• Garbage collectors collect the object when there is no object reference and reuse its memory for new object allocation. As the garbage collector doesn't delete the object, no memory is returned to the OS.

Until the objects are being referenced, JVM considers them live objects. When an object is no longer referenced and is not reachable by the application code, the garbage collector removes it and reclaims its memory. We get a question in our mind, who is the first reference in the tree of objects, right? Let's see the object tree and its roots.