Java Collection Interview Questions and Answers

1. Difference between ArrayList and Vector?

• ArrayList is not Synchronized
• ArrayList Increases size only by half
• Vector is Synchronized
• Vector Increases size by double      

    2. Difference between ArrayList and LinkedList?

• Both implement the list interface
• Searching an element in ArrayList is easy but deletion is slow
• viceversa in LinkedList 
• Searching an element in LinkedList is slow but deletion is fast
• Insertion is easy in LinkedList and slow in ArrayList
• For Random access of data use ArrayList
• For Fast Insertion and Deletion use LinkedList 

    3. Difference between Iterator and ListIterator?

• Iterator Traverse only in forward direction
• ListIterator Traverse  in both direction
• Iterator is used with both List and Set
• ListIterator is used only with List
• Iterator not allows removal of an element while iterating it
• ListIterator allows removal of an element while iterating it

    4. Difference between List and Set?

• List allows duplicate values
• Set allows only unique values

   5. Difference between List and Map?

• List contains only values
• Map contains both key and value pairs

  6. Difference between Set and Map?

• Set contains only values
• Map contains both key and value pairs

 7. Difference between HashMapand TreeMap?

• HashMap doesn't maintain an order in which the elements are inside it
• TreeMap maintains an order in which the values are inserted in it

 8. Difference between HashMap and TreeMap

• HashMap is not synchronized.
• Hashtable is synchronized.
• HashMap can contain one null key and multiple null values.
• Hashtable cannot contain any null key or null value.