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In overriding, in super class we declared a method as protected & in sub class we declared that method as private. what happens?
vinaymudgil007
- Jun 4th, 2008
Well the answer to orignal question asked is -- compilation errorlogic --> In a subclass we can't make the method more restrictive than what is there in the super class.vinny
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How System.out.println() works?
RaviKiran_CH
- Mar 18th, 2008
System is Class in Java.lang package. And Out is an Object for that Class and Println() is a method defined in that class. So once you type System.out.println() the compiler will go to the System Class and Checks whether any println() method exists or not, if so it will execute the method
jas_vineet
- Mar 14th, 2008
System is a class where the System.out is a static refrence for the PrintStream Class , also the println() is the methord for the PrintStrem Class.System.out.println is working using the native code .
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Give the scenario where hashtable and hashmap is use ?
Saurav
- Jan 5th, 2017
Hi,
The question is not about HashTable or HashMap.The question is about technical or business scenario where
hash based implementation can be used.So rather than copy paste from internet please suggest something concrete if you really have worked on.tarunarora
- Dec 2nd, 2006
Hi...to understand the basic difference b/w the two..u shd know something abt synchronization...n im assuming u upderstand synchronization in java...Scenario can be a very simple one...consider P2P (P...
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Why return type is not a part of method signature?
Ashok
- Aug 3rd, 2017
Return Type is not part of a method signature..Kindly check again and dont put wrong answer on portal because it will confuse to other.
santh kumar
- Dec 19th, 2006
It's java's Specification that describes like that the return type is not a part of method signature, whether it is method overloading or overriding. U clearly know that the type of parameters can be...
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What is markup interface? What is the purpose of markup interface?
sunil_jsr123
- Aug 25th, 2008
In Java language programming, interfaces with no methods are known as marker interfaces. Marker interfaces are Serializable, Clonable, SingleThreadModel, Event listener. Marker Interfaces are implemented by the classes or their super classes in order to add some functionality.
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Run the Tomcat Server
Hi, Is it possible to run the 2 tomcat servers simultaneously with different ports.Some times it's working. some times its not running,Anybody can help me to solve this problem.Thxregards'Punitha.R
DVishwakarma
- Feb 24th, 2010
Multiple instances of tomcat server can be run on any machine using the following steps.Copy zip installer from Apache.orgunzip in C:/Tomcatset Environment variable as CATALINA_HOME C:/TomcatJDK_HOME ...
uncer
- Jan 17th, 2010
Follow these step;1. Set JAVA_HOME=C:/JDK2 SET CATALINA_HOME=C:/TOMCAT3. CLASSPATH=C:/servlet.jav;.;jsp.jar;Then go into tomcat folder search servlet.jar copy short cut paste at desktop and double click.
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Transient and Volatile.
What is the difference between Transient and Volatile. Does volatile variable is serialized and synchronised.
Sarje
- Aug 14th, 2009
Transient State of an object can be saved (write to any file) if the class implements java.io.Serializable interface. In this case all of the field's value will be saved. If we want any of the fie...
atmarammuduli
- Jun 17th, 2008
Volatile:Threads dont cache method copy of Volatile instance variables. Each time when the var is used the thread gets latest copy.Transient:instance var not serialized ever. After deserialization its value is null(object) or zero(primitive type).
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Convert string object to primitive Integer Type
How can i convert a string object to a primitive Integer type???????Thanks
maddy_me
- Sep 18th, 2009
class StringConver{ public static void main(String[] s) { //String s1 = "Hello"; If you try this you will get NumberFormatException ...
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Implement Interface using Polymorphism
How an interface can be implemented using polymorphism?Why multiple inheritence is not used in Java?
Sarje
- Aug 18th, 2009
I think your question is how to achieve Runtime Polymorphism using using interface.then the answer is :interface MyInf{ void show();}class A implements ...
shouvanik1979
- Mar 30th, 2009
Polymorphism means "one form many actions". Lets say, a class Test implements an interface ITest. Accordingly,public interface ITest{ public void testMethod();}//a class implemen...
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Inter Thread Communication
What are all the methods used for Inter Thread communication and what is the class in which these methods are defined?
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Editorial / Best Answer
maneesh.ce.2007- Member Since Nov-2008 | Dec 15th, 2008
There are three ways in which Threads communicate with each other :
wait: It tells the calling thread to give up the monitor until some other thread enters the same monitor an calls Notify or Notifyall...
notify: It wakes up the first thread that called Wait() on the same object...
NotifyAll: It allows all the threads that called Wait() on the same object.The thread having the highest priority will run first...chakry
- Nov 5th, 2011
Why we use 'wait()' inside a synchronized method
kutiarul
- Nov 21st, 2009
Three methods are used. They are1. wait() - makes one thread wait for some time till another thread is being executed2. notify() - makes one wait process into ready state process3. notifyall() - makes all the waiting processes into ready state processes
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Arrays/Linked List
When and on what conditions will you decide whether to use linked lists or arrays, also Which process is fastest and which is slowest in arrays as well as linked list i.e, sorting, searching, add, delete etc.
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Editorial / Best Answer
Aqan12- Member Since Apr-2010 | Jun 13th, 2010
Memory:
When you create an array you allocate all the memory while initializing the array, so if you had an array of 1000 Objects, you'd allocate space to hold 1000 object references as soon as you initialize the array.LinkedList on the other hand extends dynamically as the objects are added to the linked list.
Accessing Elements:
Arrays are useful if you are going to access elements using the index. if you need to access the 100th element you can directly access it by a[100].To access 100th element in a LinkedList you'll have to traverse 99 elements to reach the 100th element.
LinkedList can handle addition/deletion of elements better then arrays and that's one of the most powerful feature of LL over arrays.
Adding/Inserting Elements:
Array is fixed size; to add a number of elements greater then the size of the array you'd have to copy the array into a new bigger array.To insert an element in the middle of an array all the elements after the inserted element would have to moved up one index.
LinkedList can grow dynamically.
Deleting Elements:
To delete an element from Array you'd have to move down all the elements after the deleted element.LinkedList elements can be deleted dynamically.
To summarize, LinkedList can handle manipulation of data structure much better and efficiently manage memory but arrays have better accessibility when accessing elements by index.
Search and Sort would be similar performance on both.jamesjohnney
- Aug 12th, 2010
In all way Linked list is best then Arrays, since its a next level of Array 1. Linked list is dynamic allocation where as Arrays are not 2. We can get and set the value with the use of get, set method...
Anubhavs
- Aug 6th, 2010
Linked list is best under the feature of the manipulation e.g. insertion, deletion etc. In the other way the array will go through a good way if we focus on the accessibility.
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When will we go for abstract class and when will we go for interface?
Praveen Kumar Singh
- Mar 13th, 2012
When you have some methods to be implemented as common and some methods you want to keep abstract, that time we will go for abstract class. You want to provide contract between class and object. And you don't want to implement any method as common that time we will go for interface.
sampra
- Mar 6th, 2012
Correct ans would be:Whenever there is need of having same common features among all subclasses of super class, we have to go for an abstract class.
Whenever there is no common features for subclasses of super class, we have to go for an interface.
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What do you like most with Ant
koti.tirumala
- Jan 5th, 2012
Memory leaks are caused by writting poor program design where Object reference are long lived and the garbage collector is unable to reclaim those objects..
javagek
- Aug 27th, 2011
I guess the best thing about ANT is that it's easier to learn and works cross platform and cross programming language - which is a real bonus.
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What is the difference between an object and an instance? And give me a real time example to differentiate these two?
Sarje
- Aug 15th, 2009
object and instance both are sameI think you want know the difference between reference and object.If so thenreference of any class type is a variable that can hold the reference(more or less we can s...
pravinsharma
- Oct 15th, 2008
An object is part of a process/thread which demands processor time through the JVM.The act of creating the object from a class is called instantiation.In literary sense an instance is existance/occurrence of an object.In this case a duplicate copy(instance) of an object is still the same object.
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Explain working of Java Virtual Machine (JVM)
nishant.mca2010
- Dec 17th, 2010
Java Virtual Machine is the heart of entire java program execution process. It is?responsible?for taking the .class file and converting each byte code instruction into the machine language instruct...
ramakrishnankt
- Apr 20th, 2009
* Creation of bytecode* Verifying the byte code* Linking the code with?library* Maintaining garbage collection
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In Execption handling What is exactly difference between throws and throw?
Karuna Reddy
- Jun 1st, 2008
Throw: We can use our own exceptions ie User Defined Exceptions.Throws: we can raise the exceptions more than one at a time
vinaymudgil007
- May 29th, 2008
Throw -- used to throw an exception explicitlyThorws -- indiacates the calling method that the called method my throw specified exceptionVinny
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Let say there are two interfaces like the followinginterface int1{int meth1();}interface int22{int meth1();}ok theni am implementing both of them in a calss as followsclass mycl implements int1,int2{}now as the rule says, if a class implements an interface it must complete its signature.now my questions is that if i define meth1(), as that method is in both interface, may i know how can i define both of that methods.please answer me
sujatham
- Aug 12th, 2007
Yes?.? int meth1()?in?both interfaces share the same implementataion in the class.
sandhya
- Apr 1st, 2007
Hi !???yes! I have chcd the above program and not giving any errors in the sense that we can use the same method in the two diff interfaces but the implementation is in the main class so this will really work ! and the expected output is printed
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What is difference between & and && in java
nehagarg2822
- Jun 1st, 2011
It depends on the type of the arguments:- For integer arguments, the single ampersand ("&")is the "bit-wise AND" operator. The double ampersand ("&&") does not mean anything as it is not defined f...
raju g
- Mar 24th, 2011
The Boolean && operator is used for determining two relational expressions and returns true if only if both returns true, otherwise returns falseThe Boolean & operator is used to perform B...
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What does the System, out, means in this statement System.out.println()?
sampra
- Mar 13th, 2012
Ystem class has a varible out 9public final static PrintStream out)and PrintStreem has a method println
Ramanjaneyulu
- Sep 3rd, 2011
println() is a method to print the messages on the screen and it is present in printStream class to access this method we need to create object of printStream class the object of printstream class cre...
Core Java Interview Questions
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