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Java Interview Questions and Answers asked in Oracle India Pvt Ltd
Company Name : Oracle
Sent By: Naresh Kumar
Interview Questions:
Concrete class: A class of only Concrete methods is called Concrete Class. For this, object instantiation is possible directly. A class can extends one class and implements many interfaces.
Abstract class:
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Interface:
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*A class of only
Concrete or only Abstract or both.
*Any java class can extend only one abstract class.
*It won’t force
the programmer to implement/override
all its methods.
*It takes less
execution time than interface.
* It allows constructor.
This class can’t be
instantiated directly.
A class must be abstract when it
consist at least one abstract method.
It gives less scope
than an Interface.
It allows both
variable & constants
declaration.
It allows methods
definitions or declarations
whenever we want.
It gives reusability
hence it can’t be declared as
“final”.
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only abstract methods.
A class can implements any no. of interfaces
(this gives multiple
interface inheritance )
It forces the
programmer to implement all its
methods
Interface takes more
execution time due to its complex
hierarchy.
* It
won’t allow any constructor.
It can’t be instantiated but it can refer to its subclass objects.
It gives more scope
than an abstract class.
By default, methods are public
abstract variables are public
static final.
It allows methods
declarations whenever we want . But it
involves complexity.
Since they give reusability hence they must not be declared as “final”.
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Yes, by making the class as final and its data members as private, final.
3) Name some struts supplied tags?
- struts_html.tld
- struts_bean.tld
- struts_logic.tld
- struts_nested.tld
- struts_template.tld
- struts_tiles.tld.
List list=new ArrayList();
list.add(“element1”);
list.add(“element2”);
list.add(“element3”);
Iterator iterator=list.iterator();
while(iterator.hasNext()){
String str=(String)itr.next();
s.o.p(string);
}
List<String> list=new ArrayList<String>();
list.add(“element1”);
list.add(“element2”);
list.add(“element3”);
for(String str:list) {
s.o.p(str);
}
5) What are versions of your current project technologies?
Java 5.0; Servlets 2.4, Jsp 2.0; struts 1.3.4 ; spring 2.0; Hibernate 3.2, Oracle 9i. weblogic 8.5.
6) What is “Quality”?
It is a Measure of excellence.state of being free from defects, deficiencies, and significant variations.
A product or service that bears its ability to satisfy stated or implied needs."
7) Can I take a class as “private”?
Yes, but it is declare to inner class, not to outer class.If we are declaring "private" to outer class nothing can be accessed from that outer class to inner class.
8) How can you clone an object?
A a1=new ();
B a11=a1.clone();
9) What methods are there in Cloneable interface?
Since Cloneable is a Marker/Tag interface, no methods present.When a class implements this interface that class obtains some special behavior and that will be realized by the JVM.
10) What is the struts latest version?
Struts 2.0
11) How are you using “Statement” like interface methods even without knowing their implementations classes in JDBC?
12) Which JSP methods can be overridden?
jspInit() & jspDestroy().
13) Explain the JSP life-cycle methods?
- Page translation: The page is parsed & a Java file containing the corresponding servlet is created
- Page compilation: The Java file is compiled.
- Load class: The compiled class is loaded.
- Create instance: An instance of the servlet is created.
- Call jspInit():This method is called before any other ethod to allow initialization.
- Call _jspService():This method is called for each request. (can’t be overridden)
- Call jspDestroy(): The container calls this when it decides take the instance out of service.It is the last method called n the servlet instance.