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HiRecently at an interview I was asked the following question:Create a hashtable A, assign key value pairs to it and then set A to null. Will it be garbage collected?Please reply.
jimmy514in
- Oct 31st, 2010
Objects which have null references are garbage collected ..But you can just request the garbage collector algo to start..you cannot command it..so when it would be collected is not known..Also, a null reference attached to object is called as weak referenceAnd weak references are garbage collected.
vinaymudgil007
- Jun 11th, 2008
Yes the hashtable would be avaliable for garbage collection BUT when actually is would be collected that would depend on JVM garbage collection cycle.vinny
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What are the difference between java.sql package and javax.sql package
vijay
- May 18th, 2012
Javax.sql provides connection pooling ,distributed transaction,disconnected rowsets
sampra
- Feb 15th, 2008
Java.sql.* package is used for the basic jdbc connections.javax.sql.* package is used for the advance jdbc. Advance is connection pooling, rowsets...ect.
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What is the difference between Assertion and Exception?
raghuprasad
- Aug 25th, 2008
There is no concept called Assertion present in Java. Exception is the program error which arises due to uncontrolable condition. This condition can be arised automatically from to program code(Eg. Da...
raj_sharma
- Aug 22nd, 2008
Exception is a mechanism used by many programming language to describe what to do when something unexpected happens.Assertion is the way to test the certain assumptions about the logic of your program.
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SetEx setEx1 = new SetEx("Java");
String str1 = new String("Java");
String str2 = new String("Java");
s.add(setEx);
s.add(setEx1);
s.add(str1);
s.add(str2);
System.out.println("No Of elements in the Set is " + s.size());
}
What is the result and how?">Import java.util.*;public class SetEx { private String str; SetEx(String s) { str = s } public static void main(String[] ar) { Set s = new HashSet(); SetEx setEx = new SetEx("Java"); SetEx setEx1 = new SetEx("Java"); String str1 = new String("Java"); String str2 = new String("Java"); s.add(setEx); s.add(setEx1); s.add(str1); s.add(str2); System.out.println("No Of elements in the Set is " + s.size()); }What is the result and how?
james.vinett
- Aug 24th, 2009
The result is 3 even though you would want it to be 2.You MUST override equals() and hashCode() for proper use of add in HashSet.
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What is "JIT ENGINE" in Java?
james.vinett
- Aug 24th, 2009
The just-in-time compiler compiles byte code into native machine language when it first encounters it and then reuses that compiled code rather than recompiling it again. This give performance gains over the interpreter model which interprets the byte code every time it encounters it.
sampra
- Feb 14th, 2008
jit reads the whole byte code and exceute once where as interpretaor does it by line by line
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What types of variables we can access inside the static inner class?
Raju
- Sep 26th, 2007
Public variable
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Explain interthread communication.
Radhakrishna P
- May 11th, 2009
When threads are running in shared resources we can manage the threads by using native methods (wait(), notify(), notifyAll()) from Object class.This is inter process communication between the threads while sharing shared resources
AjayMukiri
- Apr 30th, 2008
Java provides a basic set of synchronisation methods within java.lang.Object, allowing threads to wait for notification from other threads. Using the wait() and notify() methods, threads can synchroni...
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Difference Between Collection and Legacy classes
What are the difference between Legacy classes and Collection other than Synchronized?
udaya.kumar
- Dec 12th, 2008
Legacy Classes : Previously Collection Frame Work was not part of java.util package. Later some of the classes were re-engineered Known as Legacy Classes. Legacy Classes are SYNCRONIZED(Ctrlng accessibility over the resource).Ex:Vector/Stack/Hashtable/Dictionary/Properties.
sampra
- Feb 11th, 2008
legacy class are syncronized by defult where as collection's member are not syncronized by deflt
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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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Illegal State of Exception
When does thread throws illegal state of exception?Explain with two scenarios?
mkgraumt
- Sep 27th, 2008
Any attempt to change the status after the thread has been started, throws an IllegalThreadstateException.Scenerio 1If a thread has already started and you try to call method setDaemon(boolean) on thr...
charankk
- Apr 29th, 2008
Hi,There are one scenario where we can use it as shown below.Two threads within the JVM both gain access to the same object. One thread invalidates the object and then the other thread attempts ...
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Generating ppt through java
I am trying to generate ppt through Java using Apache POI API. I am able to create table, bulleted text etc using this API. Please answer the following two questions, if anyone is aware of this. 1. How to split text across two slides, if the row had to be broken across 2 slides because the row is so big that it can only be accommodated in 2 slide ? 2. How to re-size table cell , if the text...
ashishthakran
- Jul 28th, 2014
A list of few more Java interview questions like
1. By default, Java is pass by reference or pass by value. How does it handle?
2. In which scenario, you will use custom exceptions in Java.
3. How does garbage collection work in JavaOmen
- Nov 8th, 2013
Try this Java Library, i hope it will solve your problem:
http://www.aspose.com/java/powerpoint-component.aspx -
Serialization Process
Explain the use of serialization process in real time projects?
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Editorial / Best Answer
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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J2EE Code Standards
What are the code standard used in J2EE project in real time?
thimothyarani
- Sep 16th, 2010
Give proper name for the variable, it has to describe it functions or process. Follow coding standards
Sriram_Geek
- Aug 15th, 2010
1) Give meaningful comments.2) Give meaning variable names.3) Use lazy initialization of variables that is declare them as and when needed. Need not declare variables upfront like in C.4) Make sure yo...
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Downcasting - Superclass Reference
Explain what is superclass reference to subclass object? Why do we go for downcasting?
muralidhar.9e
- Oct 29th, 2010
Downcasting means using the super class object into the subclass.And we are cating to our sub class object.Like let's assume super and sub classesclass BaseClass{ ---...
manoj.muthavarapu
- Oct 27th, 2010
We extend a class to provide a more specialized behavior for it in the subclass. For example, consider the class "Vehicle" and imagine a subclass "Bus". All vehicle objects are cap...
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Garbage Collector
How does garbage collector decide which objects are to be removed? Can garbage collector be forced?
nishant.mca2010
- Dec 17th, 2010
Garbage collector is used to collect those objects in the Heap memory which is not referenced by any reference variable by calling System.gc() method. The purpose of GC is to delete objects that can't be reached. Only the JVM decides when to run the GC, you can only suggest it.
KhyatiK
- Nov 12th, 2010
Garbage collector removes those objects from heap memory which are no longer referred by any other objects.Using System.gc() you can call garbage collector but its not neccesary that it will run.JVM decides when the Garbage Collector will run.
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Multiple Interface
Why do we need interface concept instead of multiple inheritance? What is the drawback when we use the multiple inheritance?
sampra
- Mar 7th, 2012
Java doesnt support multiple inheritance still if we want to inheritate the one method in more than one class we can define it abstract in interface and we can use it in our class by simply implementing that interface. In this we make our class loosely coupled...
Amol
- Sep 29th, 2011
But then need to implements all methods of interface.
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Hashmap and Hashtable
which one is better and faster between hashmap and hashtable? Explain the situation where you would use them ?
sampra
- Mar 13th, 2012
HashMap is Faster then Hashtable because Hashtable has synchronized method so use Hashtable when you want synchronization other wise prefer HashMap
Naga Sudheer
- Jul 28th, 2011
Hashmap is not synchronized where as HashTable is synchronized. HashMap is faster than HashTable at the cost of synchronization and there is no point of null and value pairs in HashTable where as in HashMap it exists..so HashMap is faster than HashTable
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What is the difference between ArrayList and LinkedList
sampra
- Mar 13th, 2012
Both are similar, though slightly different in terms of goal and implementation. In a LinkedList, each element is linked to its previous and next element making it easier to delete or insert in the mi...
javagek
- Aug 28th, 2011
Arraylist: -> implements list interface hence can just behave like list. -> is more faster in situations were we want to iterate through the elements. -> uses an array as the underlying data structure...
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Abstract body
can we declare abstract body ? Explain with simple example and the situation you would use ?
krishna
- Jan 19th, 2012
Here, a ; (semicolon) is given after the method header of the first display method (with parameter). And for the second display method, keyword abstract is not stated in the header and it doesn?...
Core Java Interview Questions
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