OCJP Certification Sample Question Set-5

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    OCJP Certification Sample Question Set-5
    OCJP Certification Sample Question Set-5

    OCJP Certification Sample Question Set-5:

    Exception Handling Related:

    1) What is the difference between ‘throw’ and ‘throws’ ?And it’s application?
    Ans : Exceptions that are thrown by java runtime systems can be handled by Try and catch blocks. With throw exception we can handle the exceptions thrown by the program itself. If a method is capable of causing an exception that it does not
    handle, it must specify this behavior so the callers of the method can guard
    against that exception.

    2) What is the difference between ‘Exception’ and ‘error’ in java?
    Ans : Exception and Error are the subclasses of the Throwable class. Exception class is used for exceptional conditions that user program should catch. With exception class we can subclass to create our own custom exception.
    Error defines exceptions that are not excepted to be caught by you program. Example is Stack Overflow.

    3) What is ‘Resource leak’?
    Ans : Freeing up other resources that might have been allocated at the beginning of a method.

    4)What is the ‘finally’ block?
    Ans : Finally block will execute whether or not an exception is thrown. If an exception is thrown, the finally block will execute even if no catch statement match the exception. Any time a method is about to return to the caller from inside try/catch block, via an uncaught exception or an explicit return statement, the finally clause is also execute.

    5) Can we have catch block with out try block? If so when?
    Ans : No. Try/Catch or Try/finally form a unit.

    6) What is the difference between the following statements?
    Catch (Exception e),
    Catch (Error err),
    Catch (Throwable t)

    7) What will happen to the Exception object after exception handling?
    Ans : It will go for Garbage Collector. And frees the memory.

    8) How many Exceptions we can define in ‘throws’ clause?
    Ans : We can define multiple exceptions in throws clause.
    Signature is..
    type method-name (parameter-list) throws exception-list

    9) The finally block is executed when an exception is thrown, even if no catch matches it.
    True/False
    Ans : True

    10) The subclass exception should precede the base class exception when used within the catch clause.
    True/False
    Ans : True

    11) Exceptions can be caught or rethrown to a calling method.
    True/False
    Ans : True

    12) The statements following the throw keyword in a program are not executed.
    True/False
    Ans : True

    13) The toString ( ) method in the user-defined exception class is overridden.
    True/False
    Ans : True
    x

    Package Related

    1) What are packages ? what is use of packages ?
    Ans :The package statement defines a name space in which classes are stored.If you omit the package, the classes are put into the default package.
    Signature… package pkg;
    Use: * It specifies to which package the classes defined in a file belongs to. * Package is both naming and a visibility control mechanism.

    2) What is difference between importing “java.applet.Applet” and “java.applet.*;” ?
    Ans :”java.applet.Applet” will import only the class Applet from the package java.applet
    Where as “java.applet.*” will import all the classes from java.applet package.

    3) What do you understand by package access specifier?
    Ans : public: Anything declared as public can be accessed from anywhere
    private: Anything declared in the private can’t be seen outside of its class.
    default: It is visible to subclasses as well as to other classes in the same package.

    4) What is interface? What is use of interface?
    Ans : It is similar to class which may contain method’s signature only but not bodies.
    Methods declared in interface are abstract methods. We can implement many interfaces on a class which support the multiple inheritance.

    5) Is it is necessary to implement all methods in an interface?
    Ans : Yes. All the methods have to be implemented.

    6) Which is the default access modifier for an interface method?
    Ans : public.

    7) Can we define a variable in an interface ?and what type it should be ?
    Ans : Yes we can define a variable in an interface. They are implicitly final and static.

    8) What is difference between interface and an abstract class?
    Ans : All the methods declared inside an Interface are abstract. Where as abstract class must have at least one abstract method and others may be concrete or abstract.
    In Interface we need not use the keyword abstract for the methods.

    9) By default, all program import the java.lang package.
    True/False
    Ans : True

    10) Java compiler stores the .class files in the path specified in CLASSPATH
    environmental variable.
    True/False
    Ans : False

    11) User-defined package can also be imported just like the standard packages.
    True/False
    Ans : True

    12) When a program does not want to handle exception, the ______class is used.
    Ans : Throws

    13) The main subclass of the Exception class is _______ class.
    Ans : RuntimeException

    14) Only subclasses of ______class may be caught or thrown.
    Ans : Throwable

    15) Any user-defined exception class is a subclass of the _____ class.
    Ans : Exception

    16) The catch clause of the user-defined exception class should ______ its
    Base class catch clause.
    Ans : Exception

    17) A _______ is used to separate the hierarchy of the class while declaring an
    Import statement.
    Ans : Package

    18) All standard classes of Java are included within a package called _____.
    Ans : java.lang

    19) All the classes in a package can be simultaneously imported using ____.
    Ans : *

    20) Can you define a variable inside an Interface. If no, why? If yes, how?
    Ans.: YES. final and static

    21) How many concrete classes can you have inside an interface?
    Ans.: None

    22) Can you extend an interface?
    Ans.: Yes

    23) Is it necessary to implement all the methods of an interface while implementing the interface?
    Ans.: No

    24) If you do not implement all the methods of an interface while implementing , what specifier should you use for the class ?
    Ans.: abstract

    25) How do you achieve multiple inheritance in Java?
    Ans: Using interfaces.

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