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How to make a class immutable (like String)?
Sarje
- Aug 18th, 2009
immutable means once object is created then you can not make any change to it. if you try to do so then new object will be created and original object will be lost.final modifier is used to indicate t...
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Array List Collections
What is Use of declaring an array list object like List list = new ArrayList() rather than creating object like ArrayList arr = new ArrayList();
shailesh.pandit
- Jul 11th, 2009
We may decide later to use the?LinkedList instead of ArrayList, in this situation we just need to replace the new ArrayList() part with new LinkedList() if we keep the referance variable as List interface.whereas if we keep ArrayList as the referance variable it will be cumbersome.
R.Raj
- Jul 5th, 2008
Yes,It is possible to invoke the methods of ArrayList using the reference variable list.Infact it is used for that purpose only.
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Access Specifier
What will happen if same access specifier repeats more than once within a class?
Sarje
- Aug 17th, 2009
Multiple Acceess Specifier cannot be used with a class because it makes no sense and if you do so compile time error(wrong combination of modifiers) will be generated.
12srinu12
- Nov 7th, 2008
If the same access specifiers are used for the methods in the same class nothing will happen. Problem occurs only when all the classes in the program are assigned with same access specifiers.
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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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Object Class Methods
Why wait() and notify() are used only for threads, why not to objects?
kalaiselvigurusamy
- Jun 11th, 2010
The wait() and notify() methods are object-specific. The wait() method suspends the current thread of execution, and tells the object to keep track of the suspended thread. The notify() method tells t...
jeetu1607
- May 30th, 2010
wait(), notify() and notifyAll() are in Object class because the lock for these are set on a object and these can be called on any object. Any threads accessing the object will be put into wait status...
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Mutithreading
How synchronization can be done for multithreading environment without using the "synchronized" keyword?
Aqan12
- Apr 13th, 2010
Use java.util.concurrent package Lock mylock;try{ mylock.lock(); //critical section}finally{ mylock.unlock();} Also: try a lock with a timeout trylock() wait for some condition: condition.await() these could come handy to avoid the deadlock situations.
kvrprasadmca
- Apr 7th, 2010
We can achieve by using thread-safe collection objects like vector and all.
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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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Java.lang.object class methods
List out the five common methods in java.lang.object class?
Prabhat807
- Aug 20th, 2011
Public native int hashCode()
public string toString()
public final void wait()
public final native void notify()
public final native void notifyAll()
public boolean equals(object)
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What is heap in Java
Debananadajena
- Jul 16th, 2008
HiHeap is the location where a object is stored after it is instansiated.Means after A obj=new A();now obj will be storeed in heap.
sampra
- Feb 22nd, 2008
It is a memory area which stores all the objects created by an executing program.
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What does a static inner class mean? How is it different from any other static member
sujatham
- Jul 29th, 2007
A static member class or a static member interface comprises the same declarations as those allowed in an ordinary top-level class or interface. A static member class must be declared as a static memb...
sameer.s.abdeen
- Jun 27th, 2007
A static inner class is a static member of the enclosing classclass BigOuter{ static class Nested{}}A static inner class has no access to instance variables and non static members of the enclosing class
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What are the different kinds of exceptions? How do you catch a Runtime exception
sampra
- Feb 14th, 2008
1.Checked Exceptions Environmental error that cannot necessarily be detected by testing; e.g. disk full, broken socket, database unavailable, etc. 2.Runtime Exceptions Programming ...
Shagufta Mogal
- Oct 30th, 2007
Two kinds of exceptions:unchecked exceptions and checked exceptions.Inside the standard java.lang package ,Java defines several exception classes.Most of the exceptions are subclasses of standard type...
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What is JIT? Is it bundled with JDK? If so what is the role of interpreter(java)? plz explain in detail.
phanikhk
- Apr 9th, 2008
In a bytecode-compiled system, source code is translated to an intermediate representation known as bytecode. Bytecode is not the machine code for any particular computer, and may be portable among co...
sampra
- Feb 22nd, 2008
JIT is just-in-time. Yes JIT is bundled with JDK. Compiler converts .java file into .class file then interpreter reads bytecodes and that's why JIT.its similar to interpreator but it is faster thn interpreator
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It is essential to catch all types of exceptions
Visithra.G
- Oct 6th, 2020
It is essential to catch declare throws clause for checked exceptions unchecked exception need not be handled.
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What is the difference between ArrayList and Vector otherthan arrayList is not synchronised but Vector is?
sampra
- Feb 15th, 2008
It is similar to ArrayList, but with two differences: Vector is synchronized, and it contains many legacy methods that are not part of the collections framework.
sujatham
- Aug 10th, 2007
1. In vector the data is retrieved using the elementAt() method 2. In ArrayList, it is done using the get() method. 3. ArrayList has no default size while vector has a default size of 10.?4. ArrayLi...
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Why object class is parent for every class?
Ajay
- Sep 12th, 2018
The main reason is Inheritance. If you observe the methods in Object class, contains the basic methods that every class should contain and they are very basic features or functionalities that every class should have and support.
Also there are many reasons for that...jawaharl0207
- Oct 22nd, 2009
Because it has methods like useful for all the classes, like wait, notify, notifyall, clone and gc, these methods are common use for all classes.
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How can you do multiple inheritance in Java
sony
- Nov 27th, 2011
Its not possible directly. That means this feature is not provided by Java, but it can be achieved with the help of Interface. By implementing more than one interface
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WHEN UR USING ARRAYLIST AND LIKEDLIST AND VECTOR AND HASHMAP AND HASHTABLE?
sampra
- Feb 14th, 2008
LIST - Ordered by index, Duplicates Allowed.ARRAYLIST - Faster Iteration & fast random accessLINKEDLIST - Faster deletion, Insertion than ArryListVECTOR - Synchronized, Go ...
santu
- Sep 7th, 2007
ArrayList it is used for faster access LinkedList is for more insertation and deletion
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1)what happens if i do this=null?2)how to swap 2 variables without using third temp variable in java?3)constructors can not be inherited,why?
vinaymudgil007
- Jun 10th, 2008
The answer given above by Mr. Satish------------------------------------------------------------------------------------------a= ((a+b)-(a-b))/2b= ((a+b)+(a-b))/2--------------------------------------...
Core Java Interview Questions
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