Interview Questions and Answers for 'Java' | Search Interview Question

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Q1171. Name few tools for probing Java Memory Leaks ?

Ans. JProbe, OptimizeIt

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Q1172. Which memory areas does instance and static variables use ?

Core Java

Ans. instance variables and objects are stored on heap and the references are stored on stack whereas static variables are stored in the method area of heap.

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Q1173. 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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Q1174. What are the components of J2EE ?

Ans. applets
Client component like Client side Java codes.
Web component like JSP, Servlet WAR
Enterprise JavaBeans like Session beans, Entity beans, Message driven beans
Enterprise application like WAR, JAR, EAR

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Q1175. Difference between SAX and DOM Parser ?

Xml

Ans. A DOM (Document Object Model) parser creates a tree structure in memory from an input document whereas A SAX (Simple API for XML) parser does not create any internal structure.

A SAX parser serves the client application always only with pieces of the document at any given time whereas A DOM parser always serves the client application with the entire document no matter how much is actually needed by the client.

A SAX parser, however, is much more space efficient in case of a big input document whereas DOM parser is rich in functionality.

Use a DOM Parser if you need to refer to different document areas before giving back the information. Use SAX is you just need unrelated nuclear information from different areas.

Xerces, Crimson are SAX Parsers whereas XercesDOM, SunDOM, OracleDOM are DOM parsers.

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Q1176. What is XSD ?

Xml

Ans. XSD or Xml Schema Definition is an extension of DTD. XSD is more powerful and extensible than DTD

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Q1177. What is JAXP ?

Xml

Ans. Stands for Java API for XML Processing. This provides a common interface for creating and using SAX, DOM, and XSLT APIs in Java regardless of which vendorâ€™s implementation is actually being used.

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Q1178. What is JAXB ?

Xml

Ans. Stands for Java API for XML Binding. This standard defines a mechanism for writing out Java objects as XML and for creating Java objects from XML structures.

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Q1179. 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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Q1180. What is unmarshalling ?

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

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Q1181. 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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Q1182. What is the difference between comparable and comparator in java.util pkg?

Core Java

Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.

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Q1183. Difference between socket and servlet ?

Java EE

Ans. servlet is a small, server-resident program that typically runs automatically in response to user input.
A network socket is an endpoint of an inter-process communication flow across a computer network.

We can think of it as a difference between door and gate. They are similar as they both are entry points but they are different as they are put up at different areas.

Sockets are for low-level network communication whereas Servlets are for implementing websites and web services

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Q1184. Difference Between this() and super() ?

Core Java

Ans. 1.this is a reference to the current object in which this keyword is used whereas super is a reference used to access members specific to the parent Class.

2.this is primarily used for accessing member variables if local variables have same name, for constructor chaining and for passing itself to some method whereas super is primarily used to initialize base class members within derived class constructor.

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Q1185. 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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Q1186. Difference between the jsp scriptlet tag and jsp declaration tag?

Java EE

Ans. The jsp scriptlet tag can only declare variables not methods whereas jsp declaration tag can declare variables as well as methods.

The declaration of scriptlet tag is placed inside the _jspService() method whereas The declaration of jsp declaration tag is placed outside the _jspService() method.

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Q1187. 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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Q1188. 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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Q1189. What is race condition ?

Operating System

Ans. A source of possible errors in parallel programming, where one thread can cause an error in another thread by changing some aspect of the state of the program that the second thread is depending on (such as the value of variable).

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Q1190. 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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Q1191. 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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Q1192. What is PermGen or Permanent Generation ?

Core Java

Ans. The memory pool containing all the reflective data of the java virtual machine itself, such as class and method objects. With Java VMs that use class data sharing, this generation is divided into read-only and read-write areas. The Permanent generation contains metadata required by the JVM to describe the classes and methods used in the application. The permanent generation is populated by the JVM at runtime based on classes in use by the application. In addition, Java SE library classes and methods may be stored here.

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Q1193. What is metaspace ?

Core Java

Ans. The Permanent Generation (PermGen) space has completely been removed and is kind of replaced by a new space called Metaspace. The consequences of the PermGen removal is that obviously the PermSize and MaxPermSize JVM arguments are ignored and you will never get a java.lang.OutOfMemoryError: PermGen error.

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Q1194. 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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Q1195. 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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Q1196. 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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Q1197. 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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Q1198. 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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Q1199. 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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Q1200. 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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