Java

Final keyword

final has a different meaning depending on what it is applied to:

• Variable: Cannot be changed once initialized
• Method: Cannot be overridden by subclass
• Class: Cannot be subclassed

Finally keyword

finally is used in try/catch blocks and guarantee a section of code will execute regardless of whether an exception is thrown or not. Will be executed after try and catch statements, but before control is returned to the calling function.

This means that a return statement will still cause a finally block to be executed.

TODO: What happens if there is a return statement in a finally block?

Finalize method

The garbage collector calls the finalize method of an object just before actually destroying the object.

Overloading

Methods in Java can be overloaded, which means that the same method name exists but with different parameters (either number, argument classes, or both).

Overriding

Methods in Java can be overridden by subclasses, if the method has the same name and signature as a method in its parent class.

Garbage Collection

JVM uses a heap to create objects, and is usually allocated in advance by the OS.

Java keeps track of root objects including:

• Local Variables in the main thread
• All threads
• Static variables (unless their classes are garbage collected)

Java performs garbage collection by occasionally running through all roots and marking all reachable objects as In Use. All other objects are marked as Free and can be reused for future allocations.

Note that this means no explicit deletion, and no memory returned to the OS.

Method Parameters

Method parameters are passed by value, not reference. However, for Objects, the value is a pointer to that Object, so changing object fields can work, but reassigning the Object is impossible.

Hashcode / Equals

TODO