Difference: final, finally, finalize

• final is used to control whether a variable, method or class is "changeable".

  • variable:
    • primitive: the value can not change.
    • reference: the reference variable cannot point to any other object on the heap.
  • method: cannot be overriden
  • class: cannot be subclass

• finally is used in try/catch block to ensure a segment code is always executed.

  • always executed even if an exception is thrown or try to return/continue/break statement in the try block(except JVM exits from the try block)
  • often used to write the clean-up code. will be executed after the try and catch blocks, before return statement

• finalize() is called by Garbage Collector once it determines there is no more reference exists.

  

HashMap vs TreeMap vs LinkedHashMap

• HashMap: O(1) lookup & insertion. Implemented by an array of linked lists.
• TreeMap: O(log n) lookup & insertion. Implemented by a red-black tree.
• LinkedHashMap: O(1) lookup & insertion. Keys are ordered by their insertion order. Implemented by doubly-linked buckets.