Java Questions

What is the Difference between Enumeration and Iterator interface?

Enumeration and Iterator are the interface available in java.util package. The functionality of Enumeration interface is duplicated by the Iterator interface. New implementations should consider using Iterator in preference to Enumeration.

Iterators differ from enumerations in following ways:

Enumeration contains 2 methods namely

·        hasMoreElements()

·        nextElement()

whereas Iterator contains three methods namely

·        hasNext(),

·        next(),

·        remove().

Iterator adds an optional remove operation, and has shorter method names. Using remove() we can delete the objects but Enumeration interface does not support this feature.

Enumeration interface is used by legacy classes. Vector.elements() & Hashtable.elements() method returns Enumeration. Iterator is returned by all Java Collections Framework classes. java.util.Collection.iterator() method returns an instance of Iterator.

What are transient variables? What role do they play in Serialization process?

The transient keyword in Java is used to indicate that a field should not be serialized. Once the process of de-serialization is carried out, the transient variables do not undergo a change and retain their default value. Marking unwanted fields as transient can help you boost the serialization performance.

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