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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?...
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How would you avoid deadlocks in Java ?
prameelrian
- Nov 28th, 2011
synchronization can cause deadlocks when two threads are waiting on each other to do something. Also synchronized code has the overhead of acquiring lock, which can adversely affect the performance. ...
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Final method
having said a final method can be overloaded(default in d same class) plz explain me if there is anything missing in this code ?
class Base {
public final doSomething(Object o) {
System.out.println("Object");
}
}
class Derived extends Base {
public doSomething(Integer i) {
System.out.println("Int");santhosh
- Feb 23rd, 2012
In the main method,you simply change the "base d" as "Derived d" you get "object" and "int" as a output.also returned type is required.
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Explain When Java Application can run out of memory ?
Anon
- Apr 12th, 2012
If you have an infinite loop that keeps on doing things that take up memory (like creating objects).
sampra
- Mar 6th, 2012
We all know Java automatically garbage collects unused objects. But you must remember that an object is considered as unused only when the object no longer referenced. That means a referenced class continues to exist and to take up memory space even if it is not used.
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Adding Method in Java
Hi
I have interface in that interface 3 methods are there , after some days client said that,i want to add one more method in that interface ,so how can add 4 method so that the implemented class did not affect,
Thanks
Kalins Naik
sivapurammani
- Jul 4th, 2013
If we implement any new method in Interface then by default that method is public and abstract, So the classes which are implementing that interface should implement that method that is one way in whi...
akii
- Apr 30th, 2013
Make a class abstract in this class you do not need to implement all methods of interface .
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Platform Independence
Why platform independence is needed in real world ?
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Guess the output of the following program
Try to guess without running the program.
cpublic class IntegerClassExampleThree {
public static void main(String[] javalatte) {
Integer i = 400;
Integer j = 400;
if(i==j){
System.out.println("i==j is equal");
}else {
System.out.println("i==j is not equal");
}
}
}
public class IntegerClassExampleFour... -
Collections
What is the difference b/w 2d array and hashmap?Where we have to use this?Explain ?
Thanks in advance -
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OOPs Interface
Why interfaces is needed in Java?
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Increment and Decrements Operators
If int=8 then how to solve ++a+a--*a---a++
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1) write a program that singleton objects returns two instances?
Give me answer
ksureshbabu
- Mar 5th, 2010
class Singletones implements Serializable{ /** * */ private static final long serialVersionUID = 6240073482570369797L; &...
Jagdeep Grewal
- Nov 8th, 2005
public class CSingleton { private static CSingleton inst= null;private static int count=0;protected CSingleton() { &n...
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Explain Garbage collection mechanism in Java
sampra
- Feb 20th, 2008
Like in c and c++ we have some mechanism to create the object and some mechnaishm to distroy the object .but in java we have mechanism to create the object but we dont have any mechanism t...
nuttyvarun
- Feb 20th, 2008
Garbage collection (GC) is a form of automatic memory management. The garbage collector, or just collector, attempts to reclaim garbage, or memory used by objects that will never be accessed or mutated again by the application.
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I need some more information about interface. For Example there is no any functionality inside the method which is declared in any interface. Then why i want to implement that interface to my class. 2. Statement is an interface. When i say stmt.executeQuery(). I am getting the records in my ResultSet. How it is possible?.. since there is no functionality insid the methods which is declared in Statement Interface. What is happning here?
An idea
vinaymudgil007
- Jun 3rd, 2008
Well the answer given by sarat is a very good one & explains the concept.....
sasi
- Jul 20th, 2006
hi.....for example..take SUN as example..they provides..only interfaces..that means..they give only NULL implementations..i.e.what is the returntype of the interface..what is the method & it...
Core Java Interview Questions
Ans