1. What Is The Difference Between Serializable And Externalizable Interfaces?
Both interfaces are used for implement serialization. But, the basic difference is Serializable interface does not have any method (it’s a marker interface ) and Externalizable interface having 2 methods such as readExternal() and writeExternal(). Serializable interface is the super interface for Externalizable interface.
2. What Is An Abstract Method?
An abstract method is a method whose implementation is deferred to a subclass.
3. What Modifiers May Be Used With An Inner Class That Is A Member Of An Outer Class?
A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.
4. What Value Does Read() Return When It Has Reached The End Of A File?
The read() method returns -1 when it has reached the end of a file.
5. If A Variable Is Declared As Private, Where May The Variable Be Accessed?
A private variable may only be accessed within the class in which it is declared.
6. What Are The Types Of Class Loaders In Java?
As per my knowledge there are basically 3 types of class loader like bootstarp classloader,extension class loader and system class loader.
- Bootstrap Class Loader
- Bootstrap class loader loads java’s core classes like java.lang, java.util etc. These are classes that are part of java runtime environment. Bootstrap class loader is native implementation and so they may differ across different JVMs.
- Extensions Class Loader
- JAVA_HOME/jre/lib/ext contains jar packages that are extensions of standard core java classes. Extensions class loader loads classes from this ext folder. Using the system environment propery java.ext.dirs you can add ‘ext’ folders and jar files to be loaded using extensions class loader
- System Class Loader
- Java classes that are available in the java classpath are loaded using System class loader
7. Which Location Do You Want To Work In And Why?
Give your own choice. Also mention a valid reason for why you are interested for that location. The reason should be always positive and clear. Example :- you can support your family from this location,
8. What Restrictions Are Placed On Method Overloading?
Two methods may not have the same name and argument list but different return types.
9. What Is Downcasting ?
Downcasting is the casting from a general to a more specific type, i.e. casting down the hierarchy.
10. What Is Trient Variable?
Trient variable can’t be serialize. For example if a variable is declared as trient in a Serializable class and the class is written to an ObjectStream, the value of the variable can’t be written to the stream instead when the class is retrieved from the ObjectStream the value of the variable becomes null.
11. What Is Difference Between Iterator Access And Index Access?
Basically iterator access process the traverse operation through each element, where index access process access direct the element by using the index.
12. What Is Collection Api?
The Collection API is a set of classes and interfaces that support operation on collections of objects. These classes and interfaces are more flexible, more powerful, and more regular than the vectors, arrays, and hashtables if effectively replaces.
Example of classes: HashSet, HashMap, ArrayList, LinkedList, TreeSet and TreeMap.
Example of interfaces: Collection, Set, List and Map.
13. What Is Java Reflection Api?
Reflection is one of the most powerful api which help to work with classes, methods and variables dynamically. Basically it inspect the class attributes at runtime. Also we can say it provides a metadata about the class.
14. Describe A Problem You Faced And How You Deal With It ?
You can describe any issue you faced during your project work in the organization. And what the solution you have implemented for that issue.
15. Which Class Is Extended By All Other Classes?
The Object class is extended by all other classes.
16. What Is The % Operator?
It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.
17. Why Character Array Is Better Than String For Storing Password In Java?
Because, character array stores data in encrypted format which is not readable by human. But,the string stores the data in human readable format which is not secure.
18. How To Read And Write Image From A File ?
You can use ImageIo.read() and ImageIO.write() method of javax.imageio package.
19. What Is Daemon Thread In Java ?
A daemon thread is normally runs on background. And it does not prevent the JVM from exiting when the program finishes but the thread is still running.
20. How Many Bits Are Used To Represent Unicode, Ascii, Utf-16, And Utf-8 Characters?
Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.
21. Why Do You Want To Work In This Industry / Company?
First you should try to convince that this company gives huge opportunity in many aspect i.e. new technologies implementation, the policy of company suits you like professionalism. Also you can mention that you are big fan of this company and its your dream company. Basically show your all positive attitude towards company.
22. What Do You Understand By Private, Protected And Public?
These are accessibility modifiers. Private is the most restrictive, while public is the least restrictive. There is no real difference between protected and the default type (also known as package protected) within the context of the same package, however the protected keyword allows visibility to a derived class in a different package.
23. Can A Static Block Throw Exception?
Yes. We can throw checked exception.
24. When Can An Object Reference Be Cast To An Interface Reference?
An object reference be cast to an interface reference when the object implements the referenced interface.
25. What Is Casting?
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
26. What Is The Difference Between A Static And A Non-static Inner Class?
A non-static inner class may have object instances that are associated with instances of the class’s outer class. A static inner class does not have any object instances.
27. How Concurrenthashmap Works?
The basic design of ConcurrentHashMap is to handling threading. Basically it locks each of the box (by default 16) which can be locked independently and thread safe for operation. And it does not expose the internal lock process.
28. Which Non-unicode Letter Characters May Be Used As The First Character Of An Identifier?
The non-Unicode letter characters $ and _ may appear as the first character of an identifier.
29. What Restrictions Are Placed On The Location Of A Package Statement Within A Source Code File?
A package statement must appear as the first line in a source code file (excluding blank lines and comments).
30. Can A Byte Object Be Cast To A Double Value?
No, an object cannot be cast to a primitive value.