Java Interview Questions 4

16: Can a vector contain heterogenous objects?
A: Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.

17: Can a ArrayList contain heterogenous objects?
A: Yes a ArrayList can contain heterogenous objects. Because a ArrayList stores everything in terms of Object.

18: What is an enumeration?
A: An enumeration is an interface containing methods for accessing the underlying data structure from which the enumeration is obtained. It is a construct which collection classes return when you request a collection of all the objects stored in the collection. It allows sequential access to all the elements stored in the collection.

19: Considering the basic properties of Vector and ArrayList, where will you use Vector and where will you use ArrayList?
A: The basic difference between a Vector and an ArrayList is that, vector is synchronized while ArrayList is not. Thus whenever there is a possibility of multiple threads accessing the same instance, one should use Vector. While if not multiple threads are going to access the same instance then use ArrayList. Non synchronized data structure will give better performance than the synchronized one.

20: Can a vector contain heterogenous objects?
A: Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.