- Interview Questions and Answers for 'Intermediate' | Search Interview Question

- Interview Questions and Answers for 'Intermediate' - 107 question(s) found - Order By Rating

Q1. What are the different ways to avoid multi Threading related problems in Java ?

Ans. Synchronization,
Concurrent classes,
Volatile keyword,
Implementing concurrent Lock interface,
Immutable classes

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Q2. How many VTables are there for each class ?

Core Java

Ans. There is one VTable for each class.

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Q3. Describe structure of a Web application.

architecture

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Q4. Can we use Prototype Bean scope with Autowiring ?

Spring

Ans. Default Bean scope in auto wiring is Singleton but Yes, that can be changed by specifying the Bean scope explicitly.

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Q5. Write Java code that would cause deadlock ?

Core Java

Ans. https://howtodoinjava.com/java/multi-threading/writing-a-deadlock-and-resolving-in-java/

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Q6. How do you check memory leak in Java?

Core Java

Ans. You need to capture heap dump when it's in the healthy state. Start your application. Let it take real traffic for 10 minutes. At this point, capture heap dump. Heap Dump is basically the snapshot of your memory. It contains all objects that are residing in the memory, values stored in those objects, inbound

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Q7. what is fail fast and Fail Safe in collections?

Core Java

Ans. Iterators in java are used to iterate over the Collection objects.

Fail-Fast iterators immediately throw ConcurrentModificationException if there is any addition, removal or updation of any element.

Fail-Safe iterators don't throw any exception if a collection is structurally modified while iterating over it. This is because, they operate on the clone of the collection and not on the original collection.

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Q8. How can we ensure thread safety in static method ?

Core Java

Ans. By using synchronized static method or synchronized block

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Usually asked in relation to casting and ClassCastException.

Q9. What is instanceOf operator ? Explain it's use ?

Core Java

Ans. The operator instanceOf is used to verify if the specified object is the instance of specified class or interface.

Syntax if(x instanceOf ABC)

where x is an object reference and ABC could be a class name or interface name. The above statement will be true if x holds an object that is an instance of ABC or any of the child class of ABC or if x holds an object that implements ABC.

instanceOf operator is used to verify in case of downcasting. For ex -

DerivedClass extends BaseClass

x is the reference of BaseClass but holds DerivedClass object ( Polymorphism )

There is an operation that is defined in Derived Class, let's say derivedClassMethod()

We cannot call derivedClassMethod() directly using x as x is reference of BaseClass and not DerivedClass and hence can only access methods that are defined in BaseClass and overridden in derived class.

Though we can cast it to DerivedClass as following
((DerivedClass)x).derivedClassMethod();

But it may throw ClassCastException in case x doesn't hold an instance of DerivedClass at that point.

So before casting it to DerivedClass we may like to make sure that it is an instance of DerivedClass and hence won't throw ClassCastException.

So we make a check for it

if(x instanceOf DerivedClass) {
((DerivedClass)x).derivedClassMethod();
}

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Q10. Can we catch errors in Java ?

Core Java

Ans. Yes we can

try {
// code
} catch (Error ex) {
// handling code
}

but we shouldn't ideally do that as errors are mostly JVM based and not application based and there is rarely we can do something about it. Very likely catching and not re throwing would lead to muting their response or trace.

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Q11. What is the purpose of String Pool ? Don't you think it's a performance overhead to have unnecessary check for string in string pool ?

Core Java

Ans. String Pool makes Java more memory efficient by providing a reusable place for string literals. It might be a little performance inconvenience but results in good amount memory saving.

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Q12. Which are the most commonly used Design Patterns ?

Design

Ans. Builder ( While Writing Unit Tests )
Prototype ( Cloning )
Adapter ( asList , toString )
Chain Of Responsibility ( Logging )
Singleton
Factory ( Action Mapping )
Proxy
Observer ( Event Listener )
MVC ( Web frameworks )
Filter ( Criteria )

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Q13. How to create list that will sort it's elements dynamically?

Algorithm

Ans. Override the behavior of collection class to sort the list upon each element addition. Though it's not recommended as list are sorting heavy data structures.

List<MyType> list = new ArrayList<MyType>() {
public boolean add(MyType mt) {
super.add(mt);
Collections.sort(list, comparator);
return true;
}
};

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Q14. What is Exception Wrapping ?

Ans. Exception wrapping is wrapping an exception object within another exception object and then throwing the outer exception.

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Q15. Which is your favorite Design pattern, each in Creational , Structural and Behavioral and Why ?

Design

Ans. [Open Ended Answer]

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Q16. Name few Behavioral Design Patterns ?

Design

Ans. Interpreter,Chain of Responsibility,Command,Iterator,Observer,Mediator,Memento

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Q17. Name few structural Design Patterns ?

Design

Ans. Adapter,Bridge,Composite,Decorator,Facade,Flyweight,Proxy

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Q18. Name few creational design patterns ?

Design

Ans. Factory,Abstract Factory,Singleton,Prototype and Builder

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Q19. What will be the output of following code ?

Base Interface

public interface BaseInterface {
   int i = 4;
}

Derived Interfaces

public interface DerivedInterface1 extends BaseInterface{
   int i = 5;
}

public interface DerivedInterface2 extends BaseInterface{
   int i=6;
}

Implementing Class

public class Class implements DerivedInterface1,DerivedInterface2 {
int i=10;

public static void main(String[] args){
      System.out.println(new Class().i);
   }
}

What will be the output upon executing main and Why ?

Core Java

Ans. 10

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Q20. What will be the output of following code ?

Base Interface

public interface BaseInterface {
   int i = 4;
}

Derived Interfaces

public interface DerivedInterface1 extends BaseInterface{
   int i = 5;
}

public interface DerivedInterface2 extends BaseInterface{
   int i=6;
}

Implementing Class

public class Class implements DerivedInterface1,DerivedInterface2 {
   public static void main(String[] args){
      System.out.println(BaseInterface.i);
   }
}

What will be the output upon executing main and Why ?

Core Java

Ans. It will print 4 because member elements of an interface are implicitly static and hence the concept of overriding doesn't work.

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Q21. What is the difference between

File f = new File("homexyz.txt");

and

File f = File.createTempFile("xyz",".txt","home"); ?

Core Java

Ans. First will not create physical file in storage whereas the second will.

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Q22. Can you name some of the Java frameworks in different domains ?

Frameworks

Ans. Web Framework - Spring , Struts, Play
Dependency Injection frameworks - Google Guice , PicoContainer and Dagger
ORM Framework - Hibernate
Big Data / ETL Frameworks - Apche Hadoop , Apache Crunch, Apache Spark.
View Frameworks - JSF , Apache Wicket,jtwig.
Java Gui Frameworks - SWT , AWT, JavaFX
Testing - Junit, Mockito, PowerMock, EasyMock, JMock, JMockit
Rest Web services - Jersey , Restlet , RestX, RestEasy ,Restfulie

Here is the big list for reference - http://javasearch.buggybread.com/home2.php?keyword=

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Q23. What are the benefits of creating immutable objects ?

Core Java

Ans. 1. Security and Safety - They can be shared across multiple threads as they are thread safe. Moreover, it protects then from bad state due to interception by the other code segment. One such problem due to mutability and access by alternate code segment could be the change of hash code and then the impact on its search with hash collections.

2. Reuse - In some cases they can be reused as only one copy would exist and hence it can be relied upon. For example - String Pool

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Q24. What is memory leak ? How Java helps countering memory leaks compared to C++ ?

Core Java

Ans. Memory Leak is a situation wherein we have a reserved memory location but the program has lost its reference and hence has no way to access it.

Java doesn't have concept of Pointers, Moreover Java has concept of Garbage collection that frees up space in heap that has lost its references.

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Q25. how to access the methods of an inner class?

Core Java

Ans. It depends on the type of inner class

To access non static inner class method

new OuterClass().new InnerClass().getMethod();

To access static method of static inner class

new OuterClass.InnerClass().getMethod();

Sample Code for inner class

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Q26. Can we convert a numeric IP address to a web host name ?

Java EE

Ans. Yes, using InetAddress.getByName("<IP Address>").getHostName();

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Q27. What is an IO Filter ?

Core Java

Ans. It's an object that reads from one stream and writes to another.

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Q28. What is the difference between the Reader/Writer java.io hierarchy and the Stream class hierarchy?

Core Java

Ans. The Reader/Writer hierarchy is character oriented, whereas the Stream class hierarchy is byte oriented.

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Q29. What kind of thread is garbage collection thread ?

Core Java

Ans. Daemon thread

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Q30. What is nested interface?

Core Java

Ans. Interface that is declared inside the interface or class, is known as nested interface. It is static by default.

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