1.What is
garbage collection? What is the process that is responsible for doing that in
java?
Ans: Reclaiming the unused memory by the invalid objects. Garbage collector
is responsible for this process
2.What kind
of thread is the Garbage collector thread?
Ans: It is a daemon thread.
3.What is a
daemon thread?
Ans: These are the threads which can run without user intervention.
The JVM can exit when there are daemon thread by killing them abruptly.
4.How will
you invoke any external process in Java?
Ans: Runtime.getRuntime().exec(….)
5.What is
the finalize method do?
Ans: Before the invalid objects get garbage collected, the
JVM give the user a chance to clean up some resources before it got garbage
collected.
6.What is
mutable object and immutable object?
Ans: If a object value is changeable then we
can call it as Mutable object. (Ex., StringBuffer, …) If you are not allowed to
change the value of an object, it is immutable object. (Ex., String, Integer,
Float, …)
7.What is
the basic difference between string and stringbuffer object?
Ans: String is an
immutable object. StringBuffer is a mutable object.
8. What is
the purpose of Void class?
Ans: The Void class is an uninstantiable placeholder
class to hold a reference to the Class object representing the primitive Java
type void.
9.What is
reflection?
Ans: Reflection allows programmatic access to information about the
fields, methods and constructors of loaded classes, and the use reflected fields,
methods, and constructors to operate on their underlying counterparts on
objects, within security restrictions.
10.What is
the base class for Error and Exception?
Ans: Throwable
11.What is
the byte range?
Ans: 128 to 127
12.What is
the implementation of destroy method in java.. is it native or java code?
Ans: This method is not implemented.
13.What is a
package?
Ans: To group set of classes into a single unit is known as packaging.
Packages provides wide namespace ability.
14.What are
the approaches that you will follow for making a program very efficient?
Ans: By
avoiding too much of static methods avoiding the excessive and unnecessary use
of synchronized methods Selection of related classes based on the application
(meaning synchronized classes for multiuser and non-synchronized classes for
single user) Usage of appropriate design patterns Using cache methodologies for
remote invocations Avoiding creation of variables within a loop and lot more.
15.What is a
DatabaseMetaData?
Ans: Comprehensive information about the database as a whole.
16.What is
Locale?
Ans: A Locale object represents a specific geographical, political, or
cultural region
17.How will
you load a specific locale?
Ans: Using ResourceBundle.getBundle(…);
18.What is
JIT and its use?
Ans: Really, just a very fast compiler… In this incarnation,
pretty much a one-pass compiler — no offline computations. So you can’t look at
the whole method, rank the expressions according to which ones are re-used the
most, and then generate code. In theory terms, it’s an on-line problem.
19.Is JVM a
compiler or an interpreter?
Ans: Interpreter
20. When you
think about optimization, what is the best way to findout the time/memory
consuming process? – Using profiler
21.What is
the purpose of assert keyword used in JDK1.4.x?
Ans: In order to validate certain
expressions. It effectively replaces the if block and automatically throws the
AssertionError on failure. This keyword should be used for the critical
arguments. Meaning, without that the method does nothing.
22.How will
you get the platform dependent values like line separator, path separator,
etc., ?
Ans: Using Sytem.getProperty(…) (line.separator, path.separator, …)
23.What is
skeleton and stub? what is the purpose of those?
Ans: Stub is a client side
representation of the server, which takes care of communicating with the remote
server. Skeleton is the server side representation. But that is no more in use…
it is deprecated long before in JDK.
24.What is
the final keyword denotes?
Ans: final keyword denotes that it is the final
implementation for that method or variable or class. You can’t override that
method/variable/class any more.
25.What is
the significance of ListIterator?
Ans: You can iterate back and forth.
26.What is
the major difference between LinkedList and ArrayList?
Ans: LinkedList are meant
for sequential accessing. ArrayList are meant for random accessing.
27.What is
nested class?
Ans: If all the methods of a inner class is static then it is a
nested class.
28.What is
inner class?
Ans: If the methods of the inner class can only be accessed via the
instance of the inner class, then it is called inner class.
29.What is
composition?
Ans: Holding the reference of the other class within some other class
is known as composition.
30. What is
aggregation?
Ans: It is a special type of composition. If you expose all the
methods of a composite class and route the method call to the composite method
through its reference, then it is called aggregation.
31. What are
the methods in Object?
Ans: clone, equals, wait, finalize, getClass, hashCode,
notify, notifyAll, toString
32.Can you
instantiate the Math class?
Ans: You can’t instantiate the math class. All the
methods in this class are static. And the constructor is not public.
33.What is
singleton?
Ans: It is one of the design pattern. This falls in the creational
pattern of the design pattern.
There will be only one instance for that entire
JVM. You can achieve this by having the private constructor in the class. For
eg., public class Singleton { private static final Singleton s = new Singleton();
private Singleton() { } public static Singleton getInstance() { return s; } //
all non static methods … }
34.What is
DriverManager?
Ans: The basic service to manage set of JDBC drivers.
35. What is
Class.forName() does and how it is useful?
Ans: It loads the class into the
ClassLoader. It returns the Class. Using that you can get the instance (
“class-instance”.newInstance() ).
