-
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
-
-
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...
-
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...
-
What is the difference b/w Iterator & ListIterator
Iterator : Enables you to cycle through a collection,obtaining or removing elementsListIterator :It extends Iterator allow bidirectional traversal of list & the modification of element
sampra
- Mar 13th, 2012
Iterator : Enables you to cycle through a collection,obtaining or removing elements
ListIterator :It extends Iterator allow bidirectional traversal of list & the modification of element
lakshmijs433
- Sep 5th, 2011
Iterator is used to traverse map set and list where list iterator is used to traverse only Lists
-
Object Creation
In how many ways we can create an object? Explain with example.
Read Best Answer
Editorial / Best Answer
vishrutha- Member Since Feb-2009 | Feb 13th, 2009
1. Using new keyword
This is the most common way to create an object in java. I read somewhere that almost 99% of objects are created in this way.MyObject object = new MyObject();
2. Using Class.forName()
If we know the name of the class & if it has a public default constructor we can create an object in this way.MyObject object = (MyObject) Class.forName("subin.rnd.MyObject").newInstance();3. Using clone()
The clone() can be used to create a copy of an existing object.MyObject anotherObject = new MyObject();
MyObject object = anotherObject.clone();4. Using object deserialization
Object deserialization is nothing but creating an object from its serialized form.ObjectInputStream inStream = new ObjectInputStream(anInputStream );
MyObject object = (MyObject) inStream.readObject();5. Using class loader
one more is through creation of object using classloader likethis.getClass().getClassLoader().loadClass(com.amar.myobject).newInstance();
Now you know how to create an object. But its advised to create objects only when it is necessary to do so.
sampra
- Mar 13th, 2012
There are 5 ways:
1-> new operaotor
2-> Class.forName()
3-> Cloning
4-> Deserialization
5-> Class.newInstance()Max
- Sep 7th, 2011
All sorts of syntax sugar can also be named: 6. New String as a result of concatenation: String varName = getClass().getName(); //to avoid compile-time optimization String a = "Prefix" + varName; ...
-
Why multiple inheritance using classes is disadvantage in java
sampra
- Mar 13th, 2012
Java is build based on concept of no multiple inher to avoid memory usage and ambiguity too
A.Bava Bahrudeen
- Sep 17th, 2011
Multiple inheritance does not support in java. Because, ambiguity has been involved in the multiple inheritance in C++ language. That means, a class access the same properties of more than one class....
-
What are the roles and reasons for using Annotation in Java? Give real time demonstration example
sampra
- Mar 13th, 2012
In the annotaion we are providing the meta data. this job previously done in xml file which causes lot of mentenece.so benifit of annotaion is to mainly provide the meta data information in java file and reduce the mantinence
- Oct 28th, 2011
The usefulness of annotation can be found in J2ee,where we deal with xml files. To get the value from xml files,j2ee technology uses parsers like xerces,jdom,sax etc.Working with parser is always a h...
-
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.
-
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.
-
What is collection framework?what interfaces and classes support collection framework?
One can use different groups of objects in program using collection frame work.for more detail readcollection frame work from java.util pack.
sampra
- Mar 7th, 2012
Collection framwork is the concept to store the data. there are mainly two part in collection framework1. collection interface 2.Map interface
1.Collection-List/Set--AL/LL/Vector(C) Set (Ash set/linked hashset/Tree set)
2.Map- hash map/hashtable/tree map/linked hashmap(C)soorma
- Apr 26th, 2006
A collection is a group of object. its provide ways (using classes n interface)for fundamental alteration in the structure and architecture of many element in java.util pakageclasses>>>...
-
Importance of java.lang.obj
What is the significance of java.lang.object class?
sampra
- Mar 6th, 2012
Java.lang.Object provides several methods which are common to objects. java.lang.Class object is created whenever JVM creates an object.
Lokesh M
- Nov 29th, 2011
java.lang.Object provides several methods which are common to objects. java.lang.Class object is created whenever JVM creates an object. java.lang.Class is a superclass of all objects and it describe...
-
Implement and Extend Keywords
What is the implement, what is the extend keyword, what is the difference, give me answers in briefly ?
sampra
- Mar 6th, 2012
Implement key word is use when we have to implemet interface in that class. else we are using extends
Shivang Modi
- Oct 5th, 2011
A class can extend an another class but a class can implement an interface.
-
Why Object is Super class in Java?
sampra
- Mar 6th, 2012
Answer Question Correct Answer prabhul Answered On : Nov 21st, 2011 Based on object oriented programming,the Object class, in the java.lang package, sits at the top of the class hierarchy tree. Ever...
prabhul
- Nov 21st, 2011
Based on object oriented programming,the Object class, in the java.lang package, sits at the top of the class hierarchy tree. Every class is a descendant, direct or indirect, of the Object class. Ever...
-
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. ...
-
What is the difference between hashmap and hashset?
sampra
- Mar 6th, 2012
HashMap is not collection inteface where as HashSet is Collection interface.
HashMap class implements Map interface where as HashSet class implements Set interface.
HashMap is prints the elements orderly where as HashSet has no order, if you need some order then go for TreeSet.maheshjammula
- Nov 28th, 2011
HashSet and hashMap both are not maintained order.Difference is hashMap contains key value to map the corresponding value but hashSet have no key value and index value.Their implementations is another matter.
-
Database Driver
How to find which type driver used in Java or J2EE applications? Which type used commonly?
Lokesh M
- Nov 29th, 2011
Java.sql.Driver interface used to find and use the JDBC driver for a database. Oracle thin driver is commonly used
Code -
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?
Read Best Answer
Editorial / Best Answer
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...
-
How can we restrict class to be inherited?
kamal
- Jan 2nd, 2012
Use the final key word to do this
-
Is is true that JAVA is not 100% object oriented language ?
Core Java Interview Questions
Read Best Answer
Ans