Core Java,Struts,Spring,Hibernate,EJB,JDBC,AWT,Servlet,JSP Objective,Subjective and interview Questions with Answer
500 Java Objective Questions and Answer
Core Java Interview Questions and Answers
Q13:What are different types of access modifiers?
Ans:There are following four types of access modifiers
public: Any thing declared as public can be accessed from anywhere.
private: Any thing declared as private can’t be seen outside of its class.
protected: Any thing declared as protected can be accessed by classes in the same package and subclasses in the other packages.
default modifier : Can be accessed only to classes in the same package.
Q14 : When we can
declare a method as abstract method ?
Ans: When we have to want child class to implement the behavior of
the method.
Q15: Can We call a abstract method from a non abstract method ?
Ans : Yes, We can call a abstract method from a Non abstract method
in a Java abstract class
500 Java Objective Questions and Answer
1.Sun JAVA2 Certification Program ( Objective Questions & Answers )
2.Sun JAVA2 Certification Program (Objective Questions & Answers)
3.
Sun JAVA2 Certification Program (Objective Questions & Answers)
4.Declarations
and Access Control (Objective Questions & Answers)
5.Operator
and assignments (Objective Questions & Answers)
6.Language
fundamentals (Objective Questions & Answers)
7.Object
Oriented programming (Objective Questions & Answers)
8.Flow
Control and Exception handling (Objective Questions & Answers)
9.Fundamental
classes (Objective Questions & Answers)
10
Garbage Collection & Object Lifetime (Objective Questions & Answers)
11.Inner
classes (Objective Questions & Answers)
12.Layout
Manager (Objective Questions & Answers)
13.Threads(Objective
Questions & Answers)
14.Files
& Streams (Objective Questions & Answers)
15.Collections(Objective
Questions & Answers)
Q16: What is the difference between an Abstract class and Interface ?
And can you explain when you are using an Abstract classes ?
Ans: Abstract classes let you define some behaviors; they force
your subclasses to provide others. These abstract classes will provide the
basic functionality of your application, child class which inherited this
class will provide the functionality of the abstract methods in abstract
class. When base class calls this method, Java calls the method defined by
the child class. An Interface can only declare constants and
instance methods, but cannot implement default behavior.
Interfaces provide a form of multiple inheritance. A class can extend only
one other class.
Interfaces are limited to public methods and constants with no
implementation. Abstract classes can have a partial implementation,
protected parts, static methods, etc.
A Class may implement several interfaces. But in case of abstract class, a
class may extend only one abstract class.Interfaces are slow as it
requires extra indirection to find corresponding method in the actual
class. Abstract classes are fast.
Q17: What is user-defined exception in java ?
Ans: User-defined expectations are the exceptions defined by the
application developer which are errors related to specific application.
Application Developer can define the user defined exception by inherited
the Exception class as shown below. Using this class we can throw new
exceptions for this we have use throw keyword .
Example of user define exception Java Example :
1.Create an class which extends Exception:-
public class greaterVlaueException extends Exception {
}
2.Throw an exception using a throw statement:
public class Fund {
...
public Object getFunds() throws greaterVlaueException {
if (id>2000) throw new greaterVlaueException();
...
}
}
User-defined exceptions should usually be checked.
Q18 : What is the difference between checked and Unchecked Exceptions
in Java ?
Ans: All predefined exceptions in Java are either a checked exception
or an unchecked exception. Checked exceptions must be caught using try ..
catch() block or we should throw the exception using throws clause. If you
don't, compilation of program will fail. All exceptions in
RuntimeExcetption and Error class are unchecked exception.
Q19: Explain garbage collection ?
Ans: Garbage collection is an important part of Java's security
strategy. Garbage collection is also called automatic memory management as
JVM automatically removes the unused variables/objects from the memory.
The name "garbage collection" implies that objects that are no longer
needed by the program are "garbage" and this object will destroy by
garbage collector. A more accurate and up-to-date metaphor might be
"memory recycling." When an object is no longer referenced by the program,
the heap space it occupies must be recycled so that the space is available
for subsequent new objects. The garbage collector must somehow determine
which objects are no longer referenced by the program and make available
the heap space occupied by such unreferenced objects. In the process of
freeing unreferenced objects, the garbage collector must run any
finalizers of objects being freed.
Q20 : How you can force the garbage collection ?
Ans: Garbage collection automatic process and can't be forced. We
can call garbage collector in Java by calling System.gc() and
Runtime.gc(), JVM tries to recycle the unused objects, but there is no
guarantee when all the objects will garbage collected.
Q21 : What are the static fields & static Methods ?
Ans: If a field or method defined as a static, there is only one
copy for entire class, rather than one copy for each instance of class.
static method cannot access non-static field or call non-static method
Q22:What are the Final fields & Final Methods ?
Ans: Fields and methods can also be declared final. Final method:
A final method cannot be overridden in a subclass.
Final field: A final field is like a constant: once it has been
given a value, it cannot be assigned to again.
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500 Java Objective Questions and Answer
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