Java Interview Questions 1

Question: Parsers? DOM vs SAX parser

Answer: parsers are fundamental xml components, a bridge between XML
documents and applications that process that XML. The parser is responsible for
handling xml syntax, checking the contents of the document against constraints
established in a DTD or Schema.



Question: What is a platform?

Answer: A platform is the hardware or software environment in which a
program runs. Most platforms can be described as a combination of the operating
system and hardware, like Windows 2000/XP, Linux, Solaris, and MacOS.



Question: What is the main difference between Java platform and other
platforms?

Answer: The Java platform differs from most other platforms in that it's a
software-only platform that runs on top of other hardware-based platforms. The
Java platform has two components:



1. The Java Virtual Machine (Java VM)

2. The Java Application Programming Interface (Java API)

Question: What is the Java Virtual Machine?

Answer: The Java Virtual Machine is a software that can be ported onto
various hardware-based platforms.

Question: What is the Java API?

Answer: The Java API is a large collection of ready-made software components
that provide many useful capabilities, such as graphical user interface (GUI)
widgets.

Question: What is the package?

Answer: The package is a Java namespace or part of Java libraries. The Java
API is grouped into libraries of related classes and interfaces; these libraries
are known as packages.

Question: What is native code?

Answer: The native code is code that after you compile it, the compiled code
runs on a specific hardware platform.

Question:  Is Java code slower than native code?
 

Answer: Not really. As a platform-independent environment, the Java platform
can be a bit slower than native code. However, smart compilers, well-tuned
interpreters, and just-in-time bytecode compilers can bring performance close to
that of native code without threatening portability.

Question: What is the serialization? 

Answer: The serialization is a kind of mechanism that makes a class or a
bean persistence by having its properties or fields and state information saved
and restored to and from storage.

Question: How to make a class or a bean
serializable?

Answer: By implementing either the java.io.Serializable interface, or the
java.io.Externalizable interface. As long as one class in a class's inheritance
hierarchy implements Serializable or Externalizable, that class is serializable.

Question:  How many methods in the Serializable
interface?

Answer:There is no method in the Serializable interface. The Serializable
interface acts as a marker, telling the object serialization tools that your
class is serializable.

Question: . How many methods in the
Externalizable interface?

Answer: There are two methods in the Externalizable interface. You have to
implement these two methods in order to make your class externalizable. These
two methods are readExternal() and writeExternal().

Question:  What is the difference between
Serializalble and Externalizable interface? 

Answer: When you use Serializable interface, your class is serialized
automatically by default. But you can override writeObject() and readObject()
two methods to control more complex object serailization process. When you use
Externalizable interface, you have a complete control over your class's
serialization process.

Question: What is a transient variable?

Answer: A transient variable is a variable that may not be serialized. If
you don't want some field to be serialized, you can mark that field transient or
static.

Question:  Which containers use a border layout
as their default layout?

Answer: The Window, Frame and Dialog classes use a border layout as their
default layout.

Question: . How are Observer and Observable
used?

Answer: Objects that subclass the Observable class maintain a list of
observers. When an Observable object is updated it invokes the update() method
of each of its observers to notify the observers that it has changed state. The
Observer interface is implemented by objects that observe Observable objects.

Question:  What is synchronization and why is it
important?

Answer: With respect to multithreading, synchronization is the capability to
control the access of multiple threads to shared resources. Without
synchronization, it is possible for one thread to modify a shared object while
another thread is in the process of using or updating that object's value. This
often causes dirty data and leads to significant errors.

Question:  What are synchronized methods and
synchronized statements?

Answer: Synchronized methods are methods that are used to control access to
an object. A thread only executes a synchronized method after it has acquired
the lock for the method's object or class. Synchronized statements are similar
to synchronized methods. A synchronized statement can only be executed after a
thread has acquired the lock for the object or class referenced in the
synchronized statement.

Question: How are Observer and Observable used?

Answer: Objects that subclass the Observable class maintain a list of
observers. When an Observable object is updated it invokes the update() method
of each of its observers to notify the observers that it has changed state. The
Observer interface is implemented by objects that observe Observable objects.

Question:  What is synchronization and why is it
important? 

Answer:  With respect to multithreading, synchronization is the capability
to control the access of multiple threads to shared resources. Without
synchronization, it is possible for one thread to modify a shared object while
another thread is in the process of using or updating that object's value. This
often causes dirty data and leads to significant errors.