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Overriding Methods
Suppose a Super Class method throws an exception and this method is Overriden in the subclass with no exception. Now if you create a super class reference that has a subclass object. This throws a compile time error, Why?
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bharathnav- Member Since Oct-2008 | Oct 13th, 2008
"Suppose a Super Class method throws an exception and this method is Overriden in the subclass with no exception. Now if you create a super class reference that has a subclass object. This throws a compileLatest Answer: Because at run time, the super class will compiled first, so it will gives the run time error. ..."
if the object has been created to the subclass and both the methods are non static then the method we overriden doesn't produce any errors or exceptions.sampra
- Mar 6th, 2012
If the object has been created to the subclass and both the methods are non static then the method we overriden doesnt produce any errors or exceptions.
techbuz
- Dec 23rd, 2011
throws exception in super class doesnt affest over-riding:code eg as follows: "java public class Ride{ void clay(){ System.out.println("am in base class"); } public static voi...
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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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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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Find the Output
class A{ public static void main(String[] a){ System.out.print(String.valueOf(1)+String.valueOf(2)); String s1="s1"; String s2=s1.toString(); System.out.print(","+(s1==s2)); }}
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Which one is better when compare with Interface and Abstract class ?
muralidhar.9e
- Oct 30th, 2010
I prefer to Interface. Because the same feature can have different implementations in different Objects.And can also support for multiple Inheritance through Interfaces.If you go for Abstarct Classes ...
salman138
- Oct 29th, 2010
Both Interface and Abstract class have different usages. Interface is used to define that an object support a certain kind of functionality like any class that implements Comparable interface has the ...
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ReadLine() Function
Explain readLine function in Core Java.
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omkar.raj- Member Since Jul-2010 | Jul 8th, 2010
ReadLine() function is used to take the input from user in string format.
muralidhar.9e
- Sep 8th, 2010
Actually the readLine() method will reads the data through the bufferdReader object. It reads only one line of data through keyboard. We can't enter the multiple lines of data at runtime.This is the main functionality of the readLine() method.
sailendra.n.jena
- Aug 26th, 2010
It will read the data from the keyboard but line by line not character by character.
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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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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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Serialization Process
Explain the use of serialization process in real time projects?
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Sarje- Member Since Aug-2009 | Aug 28th, 2009
Serialization is the process of writing the state of an object to a byte stream. This is useful when you want to save the state of the object (content of the object) to a persistent storage area, such a file.
For example if you want to maintain record of the temprature on a particular place at every hour then you can serialize your object and save the temprature at every hour in a file.
Only an object that implements the java.io.Serializable interface can be saved.dh_maan
- Jun 6th, 2010
The use of serialization process in real time project is to transfer the object over the network.
winoth4
- Oct 28th, 2009
Serialization is writing the state of the object to a byte stream. This is useful when you want to save the state of the object in a persistent ?storage such as file.
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Will there be a performance penalty if you make a method synchronized? If so, can you make any design changes to improve the performance
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Answered by: Faisal Ghauri
- Jul 24th, 2005
Performance does take a hit when using synchronization. I think the way to reduce this hit is to synchronize only a block of code that will be accessed by threads and not synchronize the entire method.
sumeesudha
- Feb 6th, 2010
There is degradation in performance when you make a method synchronized. Even when a program contains only a single thread running on a single processor, a synchronized method call is still slow...
sripatnaiky
- Feb 4th, 2010
The Synchronization may be useful in avoiding the deadlock, helpful in maintaining the consistent object state etc,. Only one thread will be accessed at a time by acquiring lock on the synchronized bl...
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What is the Output of the following Java Program
public interface I1{Static String x="inside I1";public void someMethod();}class A implements I1{ public static void main(String args[[]){ System.out.println("Calling I1 var ..."+I1.x);}}
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abuthahir.d- Member Since Jan-2008 | Apr 14th, 2008
Compilation error due to 2 reasons.
1. All variables defined in the Interfaces are implicitly public static final. So need not specify "Static" in interface.
2. If any of the member functions of a Interface is not Overriden , a compilation error will be thrownshanu_rastogi
- Feb 3rd, 2010
It is right that you dont need to explicitly define a varible static but if you do so then it will not give compliler error..
sarojmohanty
- Nov 19th, 2009
Compilation error will come because you must have to override the abstract method of the implememted interface. After the implementation of the abstract method the program will compile and run properly and print "inside l1".
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Marker Interface
When there is no methods in the marker interface, then what is the use of marker interface. What is the functionality of the interface. Why do we need to implement marker interface?
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Saroj_mi2- Member Since Sep-2009 | Sep 14th, 2009
Marker interface is an interface with out having any implementation methods.
By implementing this interfaces, we will specify some special behaviour to implemented class.
Examples: Serializable, Cloneable
For example if we want to create a clone for a an object of class using clone()(clone()-- which is an object class method), then class need to implement Cloneable interface.
This mark is to JVM to handle the interface.If you are implimenting this interface the compliler will know some specific job need to be done.
For Cloneable interface even it does not have any methode the JVM looks for clone() method to execute. But the complier will not fail if the clone() meth is not implimented.
Narotam
- Jan 19th, 2010
Marker interface do not have any method. It is used only to inform JVM that?such class can do some special function like clone, serialize.
uncer
- Jan 15th, 2010
When you need to perform some behavioral function on any class without implementing method in implemented interface we implement an interface such interface called marker interface for exmple serializabe, cloneable.
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Null keyword
Is null a keyword? if not what is it?
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interviewprep9- Member Since Jun-2008 | Jun 14th, 2008
Capital N, Null is not a keyword or a reserved word.
All small letters, null is not a keyword either. but, it's a reserved word. you cannot use null as follows:
String null = "a";
null means that a reference is not pointing to any object.
Sarje
- Aug 17th, 2009
Null is not a keyword but null is reserved literal. null is the default value for instance variable.String str = null;means instance variable str does not hold reference of any object.
varmasuman
- Sep 13th, 2008
Null?means showing nothingWhenever one object reference refers null i.e? ServletConfig application=null;Then there is nothing in the object reference application.
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Difference between throw and throws
What exactly is the difference between between throw and throws? If both are used for the same purpose then why are both needed instead of one?
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vegetto- Member Since Jun-2008 | Jun 15th, 2008
hi there,
throw:the throw keyword is used to throw the exception manually,that is when you feel a particular line in your code, when executed is capable of having some exception then you use throw keyword as:
throw new MyException(arguments if any);
this leads to instantiating of the MyException class and exception is thrown
throws: this is to be used when you are not using the try catch statement in your code but you know that this particular class is capable of throwing so and so exception(only checked exceptions).in this you do not use try catch block but write using the throw clause at appropriate point in you code and the exception is thrown to caller of the method and is handeled by it. eg:
void trouble()throws IOException,any other exceptions just separate them with commas.......
{
/* throw statement at appropriate step,
no need to use try catch here,exception would be thrown to caller and u should provide try catch block to handle exception there else this process cotinues further till
appropriately it is handeled or prog terminates abruptly */
}
this is called as HANDLE OR DECLARE RULE i.e either u handle exceptions using try catch block or by declaring them
vegetto
- Jun 15th, 2008
hi there, throw:the throw keyword is used to throw the exception manually,that is when you feel a particular line in your ...
krishna_kanth83
- Jun 14th, 2008
they are not same."throws" declares that your method is capable of throwing an exception."throw" actually does the work , of throwing the exception.example :public void...
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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 to catch an Error occurred in a class
Can we catch an Error occurred in a class by extending that class with Throwable Since, Exception and error is the sub class of throwable.If yes/no- why?
sampra
- Feb 20th, 2008
We can handle the exception but we cabt handle error super call of both is throwable
onelastman
- Jan 8th, 2008
yes...u can handle that error by extending with our class with throwable...but it is not recommended to do...pls don't consider errors as same to the exceptions..both are different...Errors ...
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What is difference between string and stringtokenizer?
prasanna_b2001@yahoo.com
- Dec 16th, 2005
String and stringtokenizer serves different string operations. there is no point in comparing these two.
katam
- Nov 14th, 2005
stringtokeniser can devide the the string into tokens.where string is group of characters within " ">
Core Java Interview Questions
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