Java Questions 2

1. What is the natural order for sorting objects?
   
   Answer:
   For a collection of String objects, the natural order is alphabetical. For Integer objects, the natural order is by numeric value.

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2. What are all 3 list implementations ordered by?
   
   Answer:
   All 3 list implementations are ordered by index position, a position that you determine either by setting an object at a specific index or by adding it without specifying position,
   in which case the object is added to the end.

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3. What is the difference between an ArrayList and a LinkedList?
   
   Answer:
   In a LinkedList the elements are doubly-linked to one another.

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4. What is characterisitc of the Set Interface?
   
   Answer:
   A set cares about uniqueness and does not allow duplicates.

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5. When should you use the HashSet class?
   
   Answer:
   Use this class when you want a collection with no duplicates and you do not care about order when you iterate through it.

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6. When should you use the LinkedHashSet?
   
   Answer:
   
   1. Use this class instead of HashSet when you care about the iteration order.
   2. A LinkedHashSet lets you iterate through the elements in the order in which they were inserted.

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7. What set does TreeSet implement?
   
   Answer:
   As of Java 6, TreeSet implements NavigableSet.

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8. Which method do Maps rely on to determine whether two keys are the same or different?
   
   Answer:
   equals()

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9. When should you use a HashMap?
   
   Answer:
   When you need a Map and do not care about the order (when you iterate through it), then you should select HashMap.

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10. What are the key differences between HashMap and Hashtable?
    
    Answer:
    Hashtable is the synchronized counterpart to HashMap.
    When we say Vector and Hashtable are synchronized, we mean that the key methods of the class are synchronized.
    A HashMap lets you have null values as well as one null key, a Hashtable does not allow anything that is null.