java importent studying questions

) A class is a template for multiple objects with similar features.

a)True

b)False

Ans: a.

4) What is mean by garbage collection?

Ans: When an object is no longer referred to by any variable, Java automatically reclaims memory used by that object. This is known as garbage collection.

5) What are methods and how are they defined?

Ans: Methods are functions that operate on instances of classes in which they are defined.Objects can communicate with each other using methods and can call methods in other classes.

Method definition has four parts. They are name of the method, type of object or primitive type the method returns, a list of parameters and the body of the method. A method's signature is a combination of the first three parts mentioned above.

6) What is calling method?

Ans: Calling methods are similar to calling or referring to an instance variable. These methods are accessed using dot notation.

Ex: obj.methodname(param1,param2)

7) Which method is used to determine the class of an object?

Ans: getClass( ) method can be used to find out what class the belongs to. This class is defined in the object class and is available to all objects.

8) All the classes in java.lang package are automatically imported when a program is compiled.

a)True

b)False

Ans: a.

9) How can class be imported to a program?

Ans: To import a class, the import keyword should be used as shown.;

import classname;

10) How can class be imported from a package to a program?

Ans: import java . packagename . classname (or) import java.package name.*;

11) What is a constructor?

Ans: A constructor is a special kind of method that determines how an object is initialized when created.

12) Which keyword is used to create an instance of a class?

Ans: new.

13) Which method is used to garbage collect an object?

Ans: finalize ().

14) Constructors can be overloaded like regular methods.

a)True

b)False

Ans: a.

15) What is casting?

Ans: Casting is bused to convert the value of one type to another.

16) Casting between primitive types allows conversion of one primitive type to another.

a)True

b)False

Ans: a.

17) Casting occurs commonly between numeric types.

a)True

b)False

Ans: a.

18) Boolean values can be cast into any other primitive type.

a)True

b)False

Ans: b.

19) Casting does not affect the original object or value.

a)True

b)False

Ans: a.

20) Which cast must be used to convert a larger value into a smaller one?

Ans: Explicit cast.

21) Which cast must be used to cast an object to another class?

Ans: Specific cast.

22) Which of the following features are common to both Java & C++?

A.The class declaration

b.The access modifiers

c.The encapsulation of data & methods with in objects

d.The use of pointers

Ans: a,b,c.

23) Which of the following statements accurately describe the use of access modifiers within a class definition?

a.They can be applied to both data & methods

b.They must precede a class's data variables or methods

c.They can follow a class's data variables or methods

d.They can appear in any order

e.They must be applied to data variables first and then to methods

Ans: a,b,d.

24) Suppose a given instance variable has been declared private. Can this instance variable be manipulated by methods out side its class?

a.yes

b.no

Ans: b.

25) Which of the following statements can be used to describe a public method?

a.It is accessible to all other classes in the hierarchy

b.It is accessablde only to subclasses of its parent class

c.It represents the public interface of its class

d.The only way to gain access to this method is by calling one of the public class

methods

Ans: a,c.

26) Which of the following types of class members can be part of the internal part of a class?

a.Public instance variables

b.Private instance variables

c.Public methods

d.Private methods

Ans: b,d.

27) You would use the ____ operator to create a single instance of a named class.

a.new

b.dot

Ans: a.

28) Which of the following statements correctly describes the relation between an object and the instance variable it stores?

a.Each new object has its own distinctive set of instance variables

b.Each object has a copy of the instance variables of its class

c.the instance variable of each object are seperate from the variables of other objects

d.The instance variables of each object are stored together with the variables of other objects

Ans: a,b,c.

29) If no input parameters are specified in a method declaration then the declaration will include __.

a.an empty set of parantheses

b.the term void

Ans: a.

30) What are the functions of the dot(.) operator?

a.It enables you to access instance variables of any objects within a class

b.It enables you to store values in instance variables of an object

c.It is used to call object methods

d.It is to create a new object

Ans: a,b,c.

31) Which of the following can be referenced by this variable?

a.The instance variables of a class only

b.The methods of a class only

c.The instance variables and methods of a class

Ans: c.

32) The this reference is used in conjunction with ___methods.

a.static

b.non-static

Ans: b.

33) Which of the following operators are used in conjunction with the this and super references?

a.The new operator

b.The instanceof operator

c.The dot operator

Ans: c.

34) A constructor is automatically called when an object is instantiated

a. true

b. false

Ans: a.

35) When may a constructor be called without specifying arguments?

a. When the default constructor is not called

b. When the name of the constructor differs from that of the class

c. When there are no constructors for the class

Ans: c.

36) Each class in java can have a finalizer method

a. true

b.false

Ans: a.

37) When an object is referenced, does this mean that it has been identified by the finalizer method for garbage collection?

a.yes

b.no

Ans: b.

38) Because finalize () belongs to the java.lang.Object class, it is present in all ___.

a.objects

b.classes

c.methods

Ans: b.

39) Identify the true statements about finalization.

a.A class may have only one finalize method

b.Finalizers are mostly used with simple classes

c.Finalizer overloading is not allowed

Ans: a,c.

40) When you write finalize() method for your class, you are overriding a finalizer inherited from a super class.

a.true

b.false

Ans: a.

41) Java memory management mechanism garbage collects objects which are no longer referenced

a true

b.false

Ans: a.

42) are objects referenced by a variable candidates for garbage collection when the variable goes out of scope?

a yes

b. no

Ans: a.

43) Java's garbage collector runs as a ___ priority thread waiting for __priority threads to relinquish the processor.

a.high

b.low

Ans: a,b.

44) The garbage collector will run immediately when the system is out of memory

a.true

b.false

Ans: a.

45) You can explicitly drop a object reference by setting the value of a variable whose data type is a reference type to ___

Ans: null

46) When might your program wish to run the garbage collecter?

a. before it enters a compute-intense section of code

b. before it enters a memory-intense section of code

c. before objects are finalized

d. when it knows there will be some idle time

Ans: a,b,d

47) For externalizable objects the class is solely responsible for the external format of its contents

a.true

b.false

Ans: a

48) When an object is stored, are all of the objects that are reachable from that object stored as well?

a.true

b.false

Ans: a

49) The default__ of objects protects private and trancient data, and supports the __ of the classes

a.evolution

b.encoding

Ans: b,a.

50) Which are keywords in Java?

a) NULL

b) sizeof

c) friend

d) extends

e) synchronized

Ans : d and e

51) When must the main class and the file name coincide?

Ans :When class is declared public.

52) What are different modifiers?

Ans : public, private, protected, default, static, trancient, volatile, final, abstract.

53) What are access modifiers?

Ans : public, private, protected, default.

54) What is meant by "Passing by value" and " Passing by reference"?

Ans : objects – pass by referrence

Methods - pass by value

55) Is a class a subclass of itself?

Ans : A class is a subclass itself.

56) What modifiers may be used with top-level class?

Ans : public, abstract, final.

57) What is an example of polymorphism?

Inner class
Anonymous classes
Method overloading
Method overriding
Ans : c

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Packages and interface
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.

26) How to declare an interface example?

Ans : access class classname implements interface.

27) Can you achieve multiple interface through interface?

a)True

b) false

Ans : a.

28) Can variables be declared in an interface ? If so, what are the modifiers?

Ans : Yes. final and static are the modifiers can be declared in an interface.

29) What are the possible access modifiers when implementing interface methods?

Ans : public.

30) Can anonymous classes be implemented an interface?

Ans : Yes.

31) Interfaces can’t be extended.

a)True

b)False

Ans : b.

32) Name interfaces without a method?

Ans : Serializable, Cloneble & Remote.

33) Is it possible to use few methods of an interface in a class ? If so, how?

Ans : Yes. Declare the class as abstract.

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Exception Handling
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)

Ans :

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

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Multi Threading
1) What are the two types of multitasking?

Ans :

1.process-based

2.Thread-based

2) What are the two ways to create the thread?

Ans :

1.by implementing Runnable

2.by extending Thread

3) What is the signature of the constructor of a thread class?

Ans : Thread(Runnable threadob,String threadName)

4) What are all the methods available in the Runnable Interface?

Ans : run()

5) What is the data type for the method isAlive() and this method is available in which class?

Ans : boolean, Thread

6) What are all the methods available in the Thread class?

Ans :

1.isAlive()

2.join()

3.resume()

4.suspend()

5.stop()

6.start()

7.sleep()

8.destroy()

7) What are all the methods used for Inter Thread communication and what is the class in which these methods are defined?

Ans :

1. wait(),notify() & notifyall()

2. Object class

8) What is the mechanisam defind by java for the Resources to be used by only one Thread at a time?

Ans : Synchronisation

9) What is the procedure to own the moniter by many threads?

Ans : not possible

10) What is the unit for 1000 in the below statement?

ob.sleep(1000)

Ans : long milliseconds

11) What is the data type for the parameter of the sleep() method?

Ans : long

12) What are all the values for the following level?

max-priority

min-priority

normal-priority

Ans : 10,1,5

13) What is the method available for setting the priority?

Ans : setPriority()

14) What is the default thread at the time of starting the program?

Ans : main thread

15) The word synchronized can be used with only a method.

True/ False

Ans : False

16) Which priority Thread can prompt the lower primary Thread?

Ans : Higher Priority

17) How many threads at a time can access a monitor?

Ans : one

18) What are all the four states associated in the thread?

Ans : 1. new 2. runnable 3. blocked 4. dead

19) The suspend()method is used to teriminate a thread?

True /False

Ans : False

20) The run() method should necessary exists in clases created as subclass of thread?

True /False

Ans : True

21) When two threads are waiting on each other and can't proceed the programe is said to be in a deadlock?

True/False

Ans : True

22) Which method waits for the thread to die ?

Ans : join() method

23) Which of the following is true?

1) wait(),notify(),notifyall() are defined as final & can be called only from with in a synchronized method

2) Among wait(),notify(),notifyall() the wait() method only throws IOException

3) wait(),notify(),notifyall() & sleep() are methods of object class

1
2
3
1 & 2
1,2 & 3
Ans : D

24) Garbage collector thread belongs to which priority?

Ans : low-priority

25) What is meant by timeslicing or time sharing?

Ans : Timeslicing is the method of allocating CPU time to individual threads in a priority schedule.

26) What is meant by daemon thread? In java runtime, what is it's role?

Ans : Daemon thread is a low priority thread which runs intermittently in the background doing the garbage collection operation for the java runtime system.

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Inheritance
1) What is the difference between superclass & subclass?

Ans : A super class is a class that is inherited whereas subclass is a class that does the inheriting.

2) Which keyword is used to inherit a class?

Ans : extends

3) Subclasses methods can access superclass members/ attributes at all times?

True/False

Ans : False

4) When can subclasses not access superclass members?

Ans : When superclass is declared as private.

5) Which class does begin Java class hierarchy?

Ans : Object class

6) Object class is a superclass of all other classes?

True/False

Ans : True

7) Java supports multiple inheritance?

True/False

Ans : False

8) What is inheritance?

Ans : Deriving an object from an existing class. In the other words, Inheritance is the process of inheriting all the features from a class

9) What are the advantages of inheritance?

Ans : Reusability of code and accessibility of variables and methods of the superclass by subclasses.

10) Which method is used to call the constructors of the superclass from the subclass?

Ans : super(argument)

11) Which is used to execute any method of the superclass from the subclass?

Ans : super.method-name(arguments)

12) Which methods are used to destroy the objects created by the constructor methods?

Ans : finalize()

13) What are abstract classes?

Ans : Abstract classes are those for which instances can’t be created.

14) What must a class do to implement an interface?

Ans: It must provide all of the methods in the interface and identify the interface in its implements clause.

15) Which methods in the Object class are declared as final?

Ans : getClass(), notify(), notifyAll(), and wait()

16) Final methods can be overridden.

True/False

Ans : False

17) Declaration of methods as final results in faster execution of the program?

True/False

Ans: True

18) Final variables should be declared in the beginning?

True/False

Ans : True

19) Can we declare variable inside a method as final variables? Why?

Ans : Cannot because, local variable cannot be declared as final variables.

20) Can an abstract class may be final?

Ans : An abstract class may not be declared as final.

21) Does a class inherit the constructors of it's super class?

Ans: A class does not inherit constructors from any of it's super classes.

22) What restrictions are placed on method overloading?

Ans: Two methods may not have the same name and argument list but different return types.

23) What restrictions are placed on method overriding?

Ans : Overridden methods must have the same name , argument list , and return type. The overriding method may not limit the access of the method it overridees.The overriding method may not throw any exceptions that may not be thrown by the overridden method.

24) What modifiers may be used with an inner class that is a member of an outer class?

Ans : a (non-local) inner class may be declared as public, protected, private, static, final or abstract.

25) How this() is used with constructors?

Ans: this() is used to invoke a constructor of the same class

26) How super() used with constructors?

Ans : super() is used to invoke a super class constructor

27) Which of the following statements correctly describes an interface?

a)It's a concrete class

b)It's a superclass

c)It's a type of abstract class

Ans: c

28) An interface contains __ methods

a)Non-abstract

b)Implemented

c)unimplemented

Ans:c

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String Handling
1) Which package does define String and StringBuffer classes?

Ans : java.lang package.

2) Which method can be used to obtain the length of the String?

Ans : length( ) method.

3) How do you concatenate Strings?

Ans : By using " + " operator.

4) Which method can be used to compare two strings for equality?

Ans : equals( ) method.

5) Which method can be used to perform a comparison between strings that ignores case differences?

Ans : equalsIgnoreCase( ) method.

6) What is the use of valueOf( ) method?

Ans : valueOf( ) method converts data from its internal format into a human-readable form.

7) What are the uses of toLowerCase( ) and toUpperCase( ) methods?

Ans : The method toLowerCase( ) converts all the characters in a string from uppercase to

lowercase.

The method toUpperCase( ) converts all the characters in a string from lowercase to

uppercase.

8) Which method can be used to find out the total allocated capacity of a StrinBuffer?

Ans : capacity( ) method.

9) Which method can be used to set the length of the buffer within a StringBuffer object?

Ans : setLength( ).

10) What is the difference between String and StringBuffer?

Ans : String objects are constants, whereas StringBuffer objects are not.

String class supports constant strings, whereas StringBuffer class supports growable, modifiable strings.

11) What are wrapper classes?

Ans : Wrapper classes are classes that allow primitive types to be accessed as objects.

12) Which of the following is not a wrapper class?

String
Integer
Boolean
Character
Ans : a.

13) What is the output of the following program?

public class Question {

public static void main(String args[]) {

String s1 = "abc";

String s2 = "def";

String s3 = s1.concat(s2.toUpperCase( ) );

System.out.println(s1+s2+s3);

}

}

abcdefabcdef
abcabcDEFDEF
abcdefabcDEF
None of the above
ANS : c.

14) Which of the following methods are methods of the String class?

delete( )
append( )
reverse( )
replace( )
Ans : d.

15) Which of the following methods cause the String object referenced by s to be changed?

s.concat( )
s.toUpperCase( )
s.replace( )
s.valueOf( )
Ans : a and b.

16) String is a wrapper class?

True
False
Ans : b.

17) If you run the code below, what gets printed out?

String s=new String("Bicycle");

int iBegin=1;

char iEnd=3;

System.out.println(s.substring(iBegin,iEnd));

Bic
ic
icy
error: no method matching substring(int,char)
Ans : b.

18) Given the following declarations

String s1=new String("Hello")

String s2=new String("there");

String s3=new String();

Which of the following are legal operations?

s3=s1 + s2;
s3=s1 - s2;
s3=s1 & s2
s3=s1 && s2
Ans : a.

19) Which of the following statements are true?

a)The String class is implemented as a char array, elements are addressed using the stringname[] convention

b) Strings are a primitive type in Java that overloads the + operator for concatenation

c) Strings are a primitive type in Java and the StringBuffer is used as the matching wrapper type

d) The size of a string can be retrieved using the length property.

Ans : b.