Comparator vs Comparable in Java

1) Comparator in Java is defined in java.util package while Comparable interface in Java is defined in java.lang package, which very much says that Comparator should be used as an utility to sort objects which Comparable should be provided by default.

2) Comparator interface in Java has method public int compare (Object o1, Object o2) which returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. While Comparable interface has method public int compareTo(Object o) which returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.

3) If you see then logical difference between these two is Comparator in Java compare two objects provided to him, while Comparable interface compares "this" reference with the object specified

4) Comparable in Java is used to implement natural ordering of object. In Java API String, Date and wrapper classes implements Comparable interface.Its always good practice to override compareTo() for value objects.

5) If any class implement Comparable interface in Java then collection of that object either List or Array can be sorted automatically by using  Collections.sort() or Arrays.sort() method and object will be sorted based on there natural order defined by CompareTo method.

6)Objects which implement Comparable in Java  can be used as keys in a SortedMap like TreeMap or elements in a SortedSet  for example TreeSet, without specifying any Comparator.

Vector vs ArrayList in Java

Vector vs ArrayList in Java

Now let's see some key difference between Vector and ArrayList in Java, this will decide when is the right time to use Vector over ArrayList and vice-versa. Differences are based upon properties like synchronization, thread safety, speed, performance , navigation and Iteration over List etc.

1) Synchronization and thread-safety

First and foremost difference between Vector and ArrayList is that Vector is synchronized and ArrayList is not, what it means is that all the method which structurally modifies Vector e.g. add () or remove () are synchronized which makes it thread-safe and allows it to be used safely in a multi-threaded and concurrent environment. On the other hand ArrayList methods are not synchronized thus not suitable for use in multi-threaded environment. 

2) Speed and Performance

ArrayList is way faster than Vector. Since Vector is synchronized and thread-safe it pays price of synchronization which makes it little slow. On the other hand ArrayList is not synchronized and fast which makes it obvious choice in a single-threaded access environment. 

3) Capacity

Whenever Vector crossed the threshold specified it increases itself by value specified in capacityIncrement field while you can increase size of ArrayList by calling ensureCapacity () method.

4) Enumeration and Iterator

Vector can return enumeration of items it hold by calling elements () method which is not fail-fast as opposed to Iterator and ListIterator returned by ArrayList.

5) Legacy

Another point worth to remember is Vector is one of those classes which comes with JDK 1.0 and initially not part of Collection framework but in later version it's been re-factored to  implement List interface so that it could become part of collection framework

Serialization in Java

Serialization is the process of converting a set of object instance that contain refenece to each other into a linear stream of bytes which can be sent through a soket  store in a file or simply manipulated as a stream of data 

Object Serialization in Java is a process used to convert Object into a binary format which can be persisted into disk or sent over network to any other running Java virtual machine. Java provides Serialization API for serializing and deserializing object which includes java.io.Serializable, java.io.Externalizable, ObjectInputStream and ObjectOutputStream etc.

Serializable is a marker interfaces that tells the JVM is can write out the state of the object to some stream (basically read all the members, and write out their state to a stream, or to disk or something). The default mechanism is a binary format. You can also use it to clone things, or keep state between invocations, send objects across the network etc