Java Interview Questions-1
JAVA INTERVIEW QUESTIONS
- What do you know about Java?
Java is a high-level programming language originally developed by Sun Microsystems and
released in 1995. Java runs on a variety of platforms, such as Windows, Mac OS, and the various
versions of UNIX.
2. What are the supported platforms by Java Programming Language?
Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of
UNIX/Linux like HP-Unix, Sun Solaris, Redhat Linux, Ubuntu, CentOS, etc.
3. List any five features of Java?
Some features include Object Oriented, Platform Independent, Robust, Interpreted, Multi-threaded
4. Why is Java Architectural Neutral?
It’s compiler generates an architecture-neutral object file format, which makes the compiled code
to be executable on many processors, with the presence of Java runtime system.
5. How Java enabled High Performance?
Java uses Just-In-Time compiler to enable high performance. Just-In-Time compiler is a program
that turns Java bytecode, which is a program that contains instructions that must be interpreted
into instructions that can be sent directly to the processor.
6. Why Java is considered dynamic?
It is designed to adapt to an evolving environment. Java programs can carry extensive amount of
run-time information that can be used to verify and resolve accesses to objects on run-time.
7. What is Java Virtual Machine and how it is considered in context of Java’s platform independent
When Java is compiled, it is not compiled into platform specific machine, rather into platform
independent byte code. This byte code is distributed over the web and interpreted by virtual
Machine JVM on whichever platform it is being run.
8. List two Java IDE’s?
Netbeans, Eclipse, etc.
9. List some Java keywordsunlikeC, C + + keywords?
Some Java keywords are import, super, finally, etc.
10. What do you mean by Object?
Object is a runtime entity and it’s state is stored in fields and behavior is shown via methods.
Methods operate on an object’s internal state and serve as the primary mechanism for object-toobject
11. Define class?
A class is a blue print from which individual objects are created. A class can contain fields and
methods to describe the behavior of an object.
12. What kind of variables a class can consist of?
A class consist of Local variable, instance variables and class variables.
13. What is a Local Variable?
Variables defined inside methods, constructors or blocks are called local variables. The variable
will be declared and initialized within the method and it will be destroyed when the method has
14. What is a Instance Variable?
Instance variables are variables within a class but outside any method. These variables are
instantiated when the class is loaded.
15. What is a Class Variable?
These are variables declared with in a class, outside any method, with the static keyword.
16. What is Singleton class?
Singleton class control object creation, limiting the number to one but allowing the flexibility to
create more objects if the situation changes.
17. What do you mean by Constructor?
Constructor gets invoked when a new object is created. Every class has a constructor. If we do not
explicitly write a constructor for a class the java compiler builds a default constructor for that class.
18. List the three steps for creating an Object for a class?
An Object is first declared, then instantiated and then it is initialized.
19. What is the default value of byte datatype in Java?
Default value of byte datatype is 0.
20. What is the default value of float and double datatype in Java?
Default value of float and double datatype in different as compared to C/C++. For float its 0.0f and
for double it’s 0.0d
21. When a byte datatype is used?
This data type is used to save space in large arrays, mainly in place of integers, since a byte is four
times smaller than an int.
22. What is a static variable?
Class variables also known as static variables are declared with the static keyword in a class, but
outside a method, constructor or a block.
23. What do you mean by Access Modifier?
Java provides access modifiers to set access levels for classes, variables, methods and
constructors. A member has package or default accessibility when no accessibility modifier is
24. What is protected access modifier?
Variables, methods and constructors which are declared protected in a superclass can be
accessed only by the subclasses in other package or any class within the package of the protected
25. What do you mean by synchronized Non Access Modifier?
Java provides these modifiers for providing functionalities other than Access Modifiers,
synchronized used to indicate that a method can be accessed by only one thread at a time.
26. According to Java Operator precedence, which operator is considered to be with highest
Postfix operators i.e  . is at the highest precedence.
27. Variables used in a switch statement can be used with which datatypes?
Variables used in a switch statement can only be a byte, short, int, or char.
28. When parseInt method can be used?
This method is used to get the primitive data type of a certain String.
29. Why is String class considered immutable?
The String class is immutable, so that once it is created a String object cannot be changed. Since
String is immutable it can safely be shared between many threads ,which is considered very
important for multithreaded programming.
30. Why is StringBuffer called mutable?
The String class is considered as immutable, so that once it is created a String object cannot be
changed. If there is a necessity to make alot of modifications to Strings of characters then
StringBuffer should be used.
31. What is the difference between StringBuffer and StringBuilder class?
Use StringBuilder whenever possible because it is faster than StringBuffer. But, if thread safety is
necessary then use StringBuffer objects.
32. Which package is used for pattern matching with regular expressions?
java.util.regex package is used for this purpose.
java.util.regex consists of which classes?
java.util.regex consists of three classes − Pattern class, Matcher class and PatternSyntaxException
33. What is finalize method?
It is possible to define a method that will be called just before an object’s final destruction by the
garbage collector. This method is called finalize, and it can be used to ensure that an object
34. What is an Exception?
An exception is a problem that arises during the execution of a program. Exceptions are caught by
handlers positioned along the thread’s method invocation stack.
35. What do you mean by Checked Exceptions?
It is an exception that is typically a user error or a problem that cannot be foreseen by the
programmer. For example, if a file is to be opened, but the file cannot be found, an exception
occurs. These exceptions cannot simply be ignored at the time of compilation.
36. Explain Runtime Exceptions?
It is an exception that occurs that probably could have been avoided by the programmer. As
opposed to checked exceptions, runtime exceptions are ignored at the time of compliation.
37. Which are the two subclasses under Exception class?
The Exception class has two main subclasses : IOException class and RuntimeException Class.
38. When throws keyword is used?
If a method does not handle a checked exception, the method must declare it using the
throwskeyword. The throws keyword appears at the end of a method’s signature.
39. When throw keyword is used?
An exception can be thrown, either a newly instantiated one or an exception that you just caught,
by using throw keyword.