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Java interview questions

  • How to retrieve a key and Value from a map ? view answer
  • Why can an interface supertype call methods that belong to Object class? view answer
  • Q. What is difference between shallow copy and deep copy ? view answer
  • Q.Why to override equals() and hashCode()? and How i can implement both equals() and hashCode() for Set ? view answer
  • Q.How to sort list of objects ( User Defined) using comparator? in Descending Order. view answer
  • Q. How to sort list of objects ( User Defined) using comparator? view answer
  • What is the difference between int and Interger? view answer
  • Singleton Double-checked locking in Java? view answer
  • What are the parameters to follow Creating and Destroying Objects in Java? view answer
  • Q.What are the different scopes for Java variables? view answer
  • Q.What method must be implemented by all threads? view answer
  • Q.Can an unreachable object become reachable again? view answer
  • Q.What are the steps in the JDBC connection? view answer
  • Q.How are this() and super() used with constructors? view answer
  • Q.What is the difference between static and non-static variables? view answer
  • Q.What is the purpose of finalization? view answer
  • Q.Does garbage collection guarantee that a program will not run out of memory? view answer
  • Q.What is synchronization and why is it important? view answer
  • Q.What is daemon thread and which method is used to create the daemon thread? view answer
  • Q.What are synchronized methods and synchronized statements? view answer
  • Q.If I write System.exit (0); at the end of the try block, will the finally block still execute? view answer
  • Q.If I write return at the end of the try block, will the finally block still execute? view answer
  • Q.Is it necessary that each try block must be followed by a catch block? view answer
  • Q.What is the basic difference between the 2 approaches to exception handling. 1> try catch block and 2> specifying the candidate exceptions in the throws clause? When should you use which approach? view answer
  • Q.What are the different ways to handle exceptions? view answer
  • Q.What is the difference between error and an exception? view answer
  • Q: What is wrapper class? Explain with example? view answer
  • Q.What is serialization? Explain with example? view answer
  • Q.What one should take care of while serializing the object? view answer
  • Q. When you serialize an object, what happens to the object references included in the object? view answer
  • Q.What happens to the static fields of a class during serialization? view answer
  • Q. Objects are passed by value or by reference? view answer
  • Q. Primitive data types are passed by reference or pass by value? view answer
  • Q. What type of parameter passing does Java support? view answer
  • Q.Can a top level class be private or protected? view answer
  • Q.What is the default value of an object reference declared as an instance variable? view answer
  • Q.What is the difference between declaring a variable and defining a variable? view answer
  • Q. What are different types of inner classes? view answer
  • Q. What is Overriding? view answer
  • Q.What are Checked and UnChecked Exception? view answer
  • Q. What is final? view answer
  • Q.What is static in java? view answer
  • What is an abstract class? view answer
  • Q. What are the modifiers in Java ? view answer
  • Q.Difference between HashMap and HashTable? view answer
  • Q.Difference between Vector and ArrayList? view answer
  • Q.Difference between ArrayList and LinkedList? view answer
  • Q.What are pass by reference and passby value in Java? view answer
  • Q. When we go for Abstract and Interface in Java? view answer
  • Q.What is the difference between interface and abstract class? view answer
  • Q.What are the Garbage collection algorithms in Java? view answer
  • Q.What is garbage collection and the purpose of garbage collection in Java? view answer
  • Q. What is the difference between an Interface and an Abstract class? view answer

!!! Java interview questions !!!

Q. What is difference between shallow copy and deep copy ?



Only instances of classes that implement the Cloneable interface can be cloned. Trying to clone an object that does not implement the Cloneable interface throws a CloneNotSupportedException. Both shallow copy and deep copy object nedd to implement Cloneable Interface.

Shallow copy :

The java.lang.Object root superclass defines a clone() method.
default behavior of clone() is to return a shallow copy of the object. This means that the values of all of the original object?s fields are copied to the fields of the new object.
If a shallow copy is performed on obj1, then it is copied but its contained objects are not.
For Example:
Public class Emp
{
Private Address address;
}
Emp emp1 = new Emp();
Address add = new Address();
emp1. address= add.

If we clone
Emp emp2 = emp1.clone();
Then emp2.addess reference to the same Address object which emp1 refer.


Deep Copy :

A deep copy occurs when an object is copied along with the objects to which it refers.
A deep copy makes a distinct copy of each of the object?s fields, recursing through the entire graph of other objects referenced by the object being copied. The Java API provides no deep-copy equivalent to Object.clone(). One solution is to simply implement your own custom method (e.g., deepCopy()) that returns a deep copy of an instance of one of your classes.
Your Object Class should implements Serializable and Cloneable interface. .
public static Object copy(Object orig) {

Object obj = null;

try {

// Write the object out to a byte array

ByteArrayOutputStream bo = new ByteArrayOutputStream();

ObjectOutputStream out = new ObjectOutputStream(bo);

out.writeObject(orig);

out.flush();

out.close();

// Make an input stream from the byte array and read

// a copy of the object back in.

ObjectInputStream in = new ObjectInputStream(

new ByteArrayInputStream(bos.toByteArray()));

obj = in.readObject();

}

catch(IOException e) {

e.printStackTrace();

}

catch(ClassNotFoundException cnfe) {

cnfe.printStackTrace();

}

return obj;

}

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