Pubudu Dewagama

       Java Interview Questions

• 1      Can there be an abstract class with no abstract methods in it? Yes, But abstract method must have with abstract class.
  
  
  2.     Can an interface be final? Can’t. Because abstract methods want to implement in the last concrete class
  
  
  3.     Can interface have an inner class? Can have an inner class
  
  
  4.     Can we define private and protected modifiers for variable in the interface? Can’t. can use only finale variable and public abstract methods
  
  
  5.     What is a local, member variable?
  ·         Local – variable declared within the method called local variable
  ·         Member – variable declared within the class but not any method is called member variable
  
  
  6.     Difference between interface and abstract class?
  ·         Abstract class defines with method
  ·         Interface declares only with method
  
  
  7.     What do you mean by RMI and how it will works?
  ·         RMI – Remote Method Invocation
  ·         Can work with remote objects
  ·         Protocol – RMI-IIOP
  
  
  8.     JDBC-ODBC bridge is not multithread
  
  
  9.     Class Loader – Class loader is the one which loads class to JVM
  
  
  10.   What are the statuses of the thread?
  ·         New
  ·          
  ·         Runnable
  ·         Not Runnable
  ·         Dead
  
  
  11.   What is the socket? Socket is an endpoint for communication between two machine
  
  
  12.   How to invoke any external process in java?
  ·         Runtime.getRunTime()
  
  
  13.   What is the base class for the error and exception?
  ·         Throwable
  
  
  14.   Package?
  ·         Group of class gather into single unit called package
  
  
  15.   What is JVM? Java Virtual Machine and it is an interpreter, Totally independent from the operating system.java compiler compile the source code into Byte code and JVM reads the Byte code and convert to the machine code.JVM is the part of the JRE (Java Run time Environment)
  
  
  16.   What is the final key word denotes?
  ·         It is denotes final implements for the class, method and variables
  ·         Class – Cannot extends
  ·         Method – Cannot override
  ·         Variable – Cannot change the initialized value 
  
  
  17.   Difference between ArrayList and LinkedList?
  ·         ArrayList – Can access  randomly
  ·         LinkedList – Can access sequentially
  
  
  18.   There can be abstract class with no abstract methods but there has abstract methods it should be an abstract class
  
  
  19.   Explain different way of using threads
  ·         Implementing using runnerble interface
  ·         Extends the thread class
  
  
  20.   What are passing by reference and pass by values?
  ·         pass by reference – copy of the reference will be parsed(object)
  ·         pass by value – copy of the bit pattern will be parsed(primitives)
  
  
  21.   What is HashMap and Map?
  ·         Map is an interface
  ·         HashMap is a class
  
  
  22.   Difference between vector and ArrayList?
  ·         Vector is synchronized
  ·         ArrayList is not synchronized
  
  
  23.   Difference between Swing and AWT?
  ·         Swing – Light Weight / fast / It doesn't invoke native methods.
  ·         AWT – Heavy Weight / slow / Every graphical units it will invoke native methods
  
  
  24.   Difference between constructor and methods?
  ·         Constructer – Member function of a class
                         Same name of the class
                         No return types
                         Invokes using new operator
  ·         Methods – Is an ordinary function of a class
                    It has its own name
                    Has return type
                    Invoke using Dot (.) Operator
  
  
  25.   Define the access modifiers?
  ·         Public – public class is visible in other package
  ·         Private – variable and methods can access within the class
  ·         Protected - Is available to all classes in the same package and also available to all subclasses          
                    Of the class that owns the protected feature.
  
  
  26.   What is a marker interface? An interface with no methods
  
  
  27.   Static method cannot override, but can redeclare
  
  
  28.   What is object Oriented Programmed? It is a problem solving techniques to develop software system. it’s a techniques to think  real world in term of objects
  
  
  29.   Need Object to deal with non static variables and methods
  
  
  30.   Abstract class  cannot instantiated (Cannot create class’s object )
  
  
  31.   Don’t have multiple class inheritances , But have multiple interface inheritance
  
  
  32.   Interface/abstract class cannot instantiated.
  
  
  33.   GRASP pattern (General Responsibility Assignment Software Patterns (or Principles),)
  
  
  ·         Who should be responsible for creating a new instance of some class?  -  Creational Design Pattern
  ·         Coupling is a measure of how strongly one element is connected to, has knowledge of, or relies on other elements.
  ·         How to keep complexity manageable? – Cohesion
  
  
  34.   Reflection is commonly used by programs which require the ability to examine or modify the runtime behavior of applications running in the Java virtual machine
  
  
  35.   A Web server exclusively handles HTTP requests
  
  
  36.   Application server serves business logic to application programs through any number of protocols.
  
  
  37.   Applet is a simple java programe embedded to the web application
  
  
  38.   Java Applets are usually used to add small, interactive components or enhancements to a Webpage