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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 serialization? Explain with example?



Serialization involves saving the current state of an object to a stream, and restoring an equivalent object from that stream.

For an object to be serialized, it must be an instance of a class that implements either the Serializable or Externalizable interface. Both interfaces only permit the saving of data associated with an object's variables.
They depend on the class definition being available to the Java Virtual Machine at reconstruction time in order to construct the object.
The Serializable interface relies on the Java runtime default mechanism to save an object's state.
Writing an object is done via the writeObject() method in the ObjectOutputStream class (or the ObjectOutput interface).
Writing a primitive value may be done through the appropriate write<datatype>() method.
Reading the serialized object is accomplished using the readObject() method of the ObjectInputStream class, and primitives may be read using the various read<datatype>() methods.

The Externalizable interface specifies that the implementing class will handle the serialization on its own, instead of relying on the default runtime mechanism.
This includes which fields get written (and read), and in what order.
The class must define a writeExternal() method to write out the stream, and a corresponding readExternal() method to read the stream.
Inside of these methods the class calls ObjectOutputStream writeObject(), ObjectInputStream readObject(), and any necessary write<datatype>() and read<datatype>() methods, for the desired fields.

class DataOrder implements Serializable{
String apples, peaches, pears, cardnum, custID;
double icost;
int itotal;
}

Saving the current state of an object to a stream
DataOrder orders = new DataOrder();
FileOutputStream fos =
new FileOutputStream(orders);
ObjectOutputStream oos =
new ObjectOutputStream(fos);
oos.writeObject(order);

restoring an equivalent object from that stream
FileInputStream fis =
new FileInputStream(orders);
ObjectInputStream ois =
new ObjectInputStream(fis);
order = (DataOrder)ois.readObject();

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