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Q631. Whats the purpose of marker interfaces ?

Ans. They just tell the compiler that the objects of the classes implementing the interfaces with no defined methods need to be treated differently.

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Q632. Difference between yield() and sleeping()?

Ans. When a task invokes yield(), it changes from running state to runnable state. When a task invokes sleep(), it changes from running state to waiting/sleeping state.

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Usually asked only to fresh graduates and less experienced developers.

Q633. What is a daemon thread? Give an Example ?

Ans. These are threads that normally run at a low priority and provide a basic service to a program or programs when activity on a machine is reduced. garbage collector thread is daemon thread.

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Q634. What is the difference between AWT and Swing?

Ans. Swing provides both additional components like JTable, JTree etc and added functionality to AWT-replacement components.

Swing components can change their appearance based on the current â€œlook and feelâ€ library thatâ€™s being used.

Swing components follow the MVC paradigm, and thus can provide a much more flexible UI.

Swing provides extras for components, such as icons on many components, decorative borders for components, tool tips for components etc.

Swing components are lightweight than AWT.

Swing provides built-in double buffering ,which means an off-screen buffer is used during drawing and then the resulting bits are copied onto the screen.

Swing provides paint debugging support for when you build your own component.

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Q635. What is the order of method invocation in an applet?

Ans. public void init()
public void start()
public void stop()
public void destroy()

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Q636. Name few tools for probing Java Memory Leaks ?

Ans. JProbe, OptimizeIt

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Q637. What is J2EE? What are J2EE components and services?

Ans. J2EE or Java 2 Enterprise Edition is an environment for developing and deploying enterprise applications. The J2EE platform consists of J2EE components, services, Application Programming Interfaces (APIs) and protocols that provide the functionality for developing multi-tiered and distributed Web based applications.

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Q638. What is marshalling ?

Xml

Ans. Its the process of creating XML structures out of Java Objects which is used to traverse information across the network.

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Q639. What is unmarshalling ?

Ans. Its the process of creating Java Objects out of XML structures.

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Q640. Which load testing tools have you used ?

Ans. Rational Robot, JMeter, LoadRunner

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Q641. What are LDAP servers used for ?

Java EE

Ans. LDAP servers are typically used in J2EE applications to authenticate and authorise users. LDAP servers are hierarchical and are optimized for read access, so likely to be faster than database in providing read access.

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Q642. What are different modules of spring ?

Spring

Ans. There are seven core modules in spring

Spring MVC
The Core container
O/R mapping
DAO
Application context
Aspect Oriented Programming or AOP
Web module

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Q643. What is Spring configuration file?

Spring

Ans. Spring configuration file is an XML file. This file contains the classes information and describes how these classes are configured and introduced to each other.

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Q644. Q: What is default scope of bean in Spring framework?

Spring

Ans. The default scope of bean is Singleton.

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Very Frequently asked Spring question.

Q645. What is bean auto wiring?

Spring

Ans. The Spring container is able to autowire relationships between collaborating beans. This means that it is possible to automatically let Spring resolve collaborators (other beans) for your bean by inspecting the contents of the BeanFactory without using and elements.

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Q646. What are the phases of the JSP life cycle ?

Java EE

Ans. Translation of JSP PageCompilation of JSP PageClassloading (class file is loaded by the classloader)Instantiation (Object of the Generated Servlet is created).Initialization ( jspInit() method is invoked by the container).Reqeust processing ( _jspService() method is invoked by the container).Destroy ( jspDestroy() method is invoked by the container).

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Q647. What are JSP directives ? What are different types of directives ?

Java EE

Ans. The jsp directives are messages that tells the web container how to translate a JSP page into the corresponding servlet.

There are three types of directives -

page directive
include directive
taglib directive

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Q648. What is a Listener ?

Design

Ans. In GUI programming, an object that can be registered to be notified when events of some given type occur. The object is said to listener? for the events.

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Q649. What is the following code doing ?

private static final String[] COLORS = new String[] { "Red", "Green", "Blue" };

Core Java

Ans. We are initializing a static and constant string array named as COLORS using Strings "Red","Green" and "Blue".

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Q650. What is unicode ?

Core Java

Ans. A way of encoding characters as binary numbers. The Unicode character set includes
characters used in many languages, not just English. Unicode is the character set that is
used internally by Java.

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Q651. What is ThreadFactory ?

Core Java

Ans. ThreadFactory is an interface that is meant for creating threads instead of explicitly creating threads by calling new Thread(). Its an object that creates new threads on demand. Using thread factories removes hardwiring of calls to new Thread, enabling applications to use special thread subclasses, priorities, etc.

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Q652. What is the benefit of inner / nested classes ?

Core Java

Ans. You can put related classes together as a single logical group.

Nested classes can access all class members of the enclosing class, which might be useful in certain cases.

Nested classes are sometimes useful for specific purposes. For example, anonymous inner classes are useful for writing simpler event-handling code with AWT/Swing.

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Q653. Explain Static nested Classes ?

Ans. The accessibility (public, protected, etc.) of the static nested class is defined by the outer class.

A static nested class is not an inner class, it's a top-level nested class.

The name of the static nested class is expressed with OuterClassName.NestedClassName syntax.

When you define an inner nested class (or interface) inside an interface, the nested class is declared implicitly public and static.

Static nested classes can be declared abstract or final.

Static nested classes can extend another class or it can be used as a base class.

Static nested classes can have static members.

Static nested classes can access the members of the outer class (only static members, obviously).

The outer class can also access the members (even private members) of the nested class through an object of nested class. If you don't declare an instance of the nested class, the outer class cannot access nested class elements directly.

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Q654. Explain Inner Classes ?

Core Java

Ans. The accessibility (public, protected, etc.) of the inner class is defined by the outer class.

Just like top-level classes, an inner class can extend a class or can implement interfaces.

Similarly, an inner class can be extended by other classes, and an inner interface can be implemented or extended by other classes or interfaces.

An inner class can be declared final or abstract.Inner classes can have inner classes, but you will have a hard time reading or understanding such complex nesting of classes.

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Q655. Explain Method Local Inner Classes ?

Core Java

Ans. You can create a non-static local class inside a body of code. Interfaces cannot have local classes, and you cannot create local interfaces.

Local classes are accessible only from the body of the code in which the class is defined. The local classes are completely inaccessible outside the body of the code in which the class is defined.

You can extend a class or implement interfaces while defining a local class.

A local class can access all the variables available in the body of the code in which it is defined. You can pass only final variables to a local inner class.

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Q656. Explain about anonymous inner classes ?

Core Java

Ans. Anonymous classes are defined in the new expression itself, so you cannot create multiple objects of an anonymous class.

You cannot explicitly extend a class or explicitly implement interfaces when defining an anonymous class.

An anonymous inner class is always created as part of a statement; don't forget to close the statement after the class definition with a curly brace. This is a rare case in Java, a curly brace followed by a semicolon.

Anonymous inner classes have no name, and their type must be either a subclass of the named type or an implementer of the named interface

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Q657. What will happen if class implement two interface having common method?

Ans. That would not be a problem as both are specifying the contract that implement class has to follow.
If class C implement interface A & interface B then Class C thing I need to implement print() because of interface A then again Class think I need to implement print() again because of interface B, it sees that there is already a method called test() implemented so it's satisfied.

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Q658. What is the advantage of using arrays over variables ?

Ans. Arrays provide a structure wherein multiple values can be accessed using single reference and index. This helps in iterating over the values using loops.

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Q659. Difference between Class#getInstance() and new operator ?

Ans. Class.getInstance doesn't call the constructor whereas if we create an object using new operator , we need to have a matching constructor or copiler should provide a default constructor.

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Q660. Can we create an object if a Class doesn't have any constructor ( not even the default provided by constructor ) ?

Ans. Yes , using Class.getInstance.

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