Shallow Cloning and Deep Cloning in Java

Cloning is of 2 Types:

1. Shallow Cloning  2. Deep Cloning

Whenever clone() method is used 2 different objects are created in 2 different memory locations. So
separate memory is occupied.

If a class contains  X, Y variable and clone is applied two different objects are created in two different situations.

In Shallow Cloning  main problem is instance variables are common for both objects , so if one object is modifed then automatically second object is also modified.

In deep cloning 2 different objects are created in 2 different memory locations , if in case original object is modified then also its duplicate object won't effect , why because there is  no relation between original and duplicate object.

KNOWLEDGE HUB: How many ways can you create an object in Java

KNOWLEDGE HUB: How many ways can you create an object in Java

different ways to create an object in Java

There are 4 ways of creating objects in Java.

1. Using new operator

Employee emp = new Employee();

Here , we are creating Employee class object  'emp' using new operator.

2. Using factrory methods:

NumberFormat nf  = NumberFormat.getNumberInstace();

Here, we are creatig NumberFormat object using the factory method getNumberInstacne().

3. Using newInstance() method .

(a) First,store the class name  'Employee' as string into an  object. For this purpose , factory method
forName() of the class 'Class' will be useful.

Class c = Class.forName("Employee");

Note: class with the name 'Class' in java.lang package.
(b) create another object to the class whose name is in the object c . For this purpose , we need
newInstance()  method of the class 'Class' . as:

Employee obj = (Employee)c.newInstance();

4. By cloning an already available object, we can create another object . Creating exact copy of an
existing object is called 'cloning':

Employee obj1 = new Employee();
Employee obj2 = (Employee)obj1.clone();

Constructor VS Method in Java

Constructor	Method
A constructor is used to initialize the instance variables of a class.	A Method is used for any general purpose processing or calculations.
A constructors name and class name should be same.	A method’s name and class name can be same or different.
A constructor is called at the time of creating the object.	A method can be called after creating the object.
A Constructor  is called only once per object.	A method can be called several times on the object.
A constructor is called and executed automatically.	A method is executed only when we call it.

Difference between Set and List in Java

Set:

1. A set represents a collection of elements . Order of the elements may change in the set.
2. Set will not allow duplicate values to be stored.
3. Accessing elements by their index(position number) is not possible in case of sets.
4.Sets will not allow null elements.

List:

1. A List represents ordered collection of elements . List preserves the order of elements in
which they are entered.
2. List will allow duplicate value.
3.Accessing elements by index is possible in lists.
4. Lists allow null elements to be stored.

Difference between HashMap and Hashtable in Java

HashMap:

1. HashMap object is not synchronized by default.
2. In case of a single thread , using HashMap is faster than the Hashtable.
3. HashMap allows null keys and null values to be stored.
4. Iterator in the HashMap is fail-fast . This means iterator will produce exception if concurrent
updates are made to the HashMap.
5. We can make HashMap object synchronied using synchronizedMap() method as:

Collections.synchronizedMap(new HashMap())

Hashtable:

1. Hashtable object is synchronized by default.
2.In case fo multiple threads , using Hashtable is advisable. With a single thread, Hashtable
becomes slow.
3.Hashtable does not allow null keys or values.
4.Enumeration for the Hashtable is not fail-fast. This means even if concurrent updations
are done to to Hashtable, there will not be any incorrect results produced by the Enumeration.

Difference between ArrayList and Vector in Java

ArrayList:
---------------
1.Array List object is not synchronized by default.
2.In case of a single thread ,using ArrayList is faster than the vector.
3.ArrayList increases its size every time by 50 percent(half).

4. We can synchronize Arraylist using synchronizedList() mehtod as:

List  l = Collections.SynchronizedList(new ArrayList());

Vector:
--------
1.Vector object is synchronized by default.
2. In case of multiple threads, using Vector is advisable. With a single  thread,
   Vector becomes slow.
3. Vector increases its size every time by doubling it.