Introduction to Cassandra

Apache Cassandra is a NoSQL persistence solu- ton that ofers distributed data, linear scalability, and a tunable consistency level, making it well suited for highly available and high- volume applicatons. Devel- oped by Facebook and open sourced in 2008, Cassandra was infuenced by the Bigtable and Dynamo white papers. Dynamo inspired the parttoning and repli- caton in Cassandra, while Cassandra’s log-structured Column Family data model— which stores data associated with a key in a schemaless way—is similar to Bigtable. Cassandra is used by many big names in the online industry including Netfix, eBay, Twiter, and reddit.

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Java Apps on iOS and Android— Now a Reality

Let me guess a couple of things about you. First, you are fuent in Java. Second, you have a smartphone, tablet, or both within reach. Am I right? Well, with the explosion of mobile device popularity, plus the fact that you are reading Java Magazine, these were not really tough guesses to make.


What might be a bit tougher is answering this queston: How do you take your Java skills and start building applicatons for the mobile devices that you—and your customers—have? That is the focus of this artcle.

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DBMS Basics - Interview Questions and Answers

1. What is database?

A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose.

2. What is DBMS?

It is a collection of programs that enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications.

3. What is a Database system?

The database and DBMS software together is called as Database system.

4. What are the advantages of DBMS?

1. Redundancy is controlled.
2. Unauthorised access is restricted.
3. Providing multiple user interfaces.
4. Enforcing integrity constraints.
5. Providing backup and recovery.

5. What are the disadvantage in File Processing System?

1. Data redundancy and inconsistency.
2. Difficult in accessing data.
3. Data isolation.
4. Data integrity.
5. Concurrent access is not possible.
6. Security Problems.

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Java Exception Interview Questions and Answers

1. What is Exception in Java?

   Exception is an error event that can happen during the execution of a program and disrupts it’s normal flow. Exception can arise from different kind of situations such as wrong data entered by user, hardware failure, network connection failure etc.
   Whenever any error occurs while executing a java statement, an exception object is created and then JRE tries to find exception handler to handle the exception. If suitable exception handler is found then the exception object is passed to the handler code to process the exception, known as catching the exception. If no handler is found then application throws the exception to runtime environment and JRE terminates the program.
   Java Exception handling framework is used to handle runtime errors only, compile time errors are not handled by exception handling framework.



2. What are the Exception Handling Keywords in Java?

   There are four keywords used in java exception handling.
   
   1. throw: Sometimes we explicitly want to create exception object and then throw it to halt the normal processing of the program. throw keyword is used to throw exception to the runtime to handle it.
   2. throws: When we are throwing any checked exception in a method and not handling it, then we need to use throws keyword in method signature to let caller program know the exceptions that might be thrown by the method. The caller method might handle these exceptions or propagate it to it’s caller method using throws keyword. We can provide multiple exceptions in the throws clause and it can be used with main() method also.
   3. try-catch: We use try-catch block for exception handling in our code. try is the start of the block and catch is at the end of try block to handle the exceptions. We can have multiple catch blocks with a try and try-catch block can be nested also. catch block requires a parameter that should be of type Exception.
   4. finally: finally block is optional and can be used only with try-catch block. Since exception halts the process of execution, we might have some resources open that will not get closed, so we can use finally block. finally block gets executed always, whether exception occurrs or not.

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Java Multi-Threading and Concurrency Interview Questions with Answers

1. What is the difference between Process and Thread?

   A process is a self contained execution environment and it can be seen as a program or application whereas Thread is a single task of execution within the process. Java runtime environment runs as a single process which contains different classes and programs as processes. Thread can be called lightweight process. Thread requires less resources to create and exists in the process, thread shares the process resources.



2. What are the benefits of multi-threaded programming?

   In Multi-Threaded programming, multiple threads are executing concurrently that improves the performance because CPU is not idle incase some thread is waiting to get some resources. Multiple threads share the heap memory, so it’s good to create multiple threads to execute some task rather than creating multiple processes. For example, Servlets are better in performance than CGI because Servlet support multi-threading but CGI doesn’t.
   

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Java String Interview Questions and Answers

What is String in Java? String is a data type?

String is a Class in java and defined in java.lang package. It’s not a primitive data type like int and long. String class represents character Strings. String is used in almost all the Java applications and there are some interesting facts we should know about String. String in immutable and final in Java and JVM uses String Pool to store all the String objects.
Some other interesting things about String is the way we can instantiate a String object using double quotes and overloading of “+” operator for concatenation.

What are different ways to create String Object?

We can create String object using new operator like any normal java class or we can use double quotes to create a String object. There are several constructors available in String class to get String from char array, byte array, StringBuffer and StringBuilder.

1 2	String str = new String("abc"); String str1 = "abc";

When we create a String using double quotes, JVM looks in the String pool to find if any other String is stored with same value. If found, it just returns the reference to that String object else it creates a new String object with given value and stores it in the String pool.
When we use new operator, JVM creates the String object but don’t store it into the String Pool. We can use intern() method to store the String object into String pool or return the reference if there is already a String with equal value present in the pool.

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Java Collections Interview Questions Answers

1. What are Collection related features in Java 8?

   Java 8 has brought major changes in the Collection API. Some of the changes are:
   
   1. Java Stream API for collection classes for supporting sequential as well as parallel processing
   2. Iterable interface is extended with forEach() default method that we can use to iterate over a collection. It is very helpful when used with lambda expressions because it’s argument Consumer is a function interface.
   3. Miscellaneous Collection API improvements such as forEachRemaining(Consumer action) method in Iterator interface, Map replaceAll(), compute(), merge() methods.



2. What is Java Collections Framework? List out some benefits of Collections framework?

   Collections are used in every programming language and initial java release contained few classes for collections: Vector, Stack, Hashtable, Array. But looking at the larger scope and usage, Java 1.2 came up with Collections Framework that group all the collections interfaces, implementations and algorithms.
   Java Collections have come through a long way with usage of Generics and Concurrent Collection classes for thread-safe operations. It also includes blocking interfaces and their implementations in java concurrent package.
   Some of the benefits of collections framework are;
   
   • Reduced development effort by using core collection classes rather than implementing our own collection classes.
   • Code quality is enhanced with the use of well tested collections framework classes.
   • Reduced effort for code maintenance by using collection classes shipped with JDK.
   • Reusability and Interoperability

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Core Java Interview Questions and Answers

1. What are the important features of Java 8 release?

   Java 8 has been released in March 2014, so it’s one of the hot topic in java interview questions. If you answer this question clearly, it will show that you like to keep yourself up-to-date with the latest technologies.
   Java 8 has been one of the biggest release after Java 5 annotations and generics. Some of the important features of Java 8 are:
   
   1. Interface changes with default and static methods
   2. Functional interfaces and Lambda Expressions
   3. Java Stream API for collection classes
   4. Java Date Time API
   I strongly recommend to go through above links to get proper understanding of each one of them, also read Java 8 Features.



2. What do you mean by platform independence of Java?

   Platform independence means that you can run the same Java Program in any Operating System. For example, you can write java program in Windows and run it in Mac OS.



3. What is JVM and is it platform independent?

   Java Virtual Machine (JVM) is the heart of java programming language. JVM is responsible for converting byte code into machine readable code. JVM is not platform independent, thats why you have different JVM for different operating systems. We can customize JVM with Java Options, such as allocating minimum and maximum memory to JVM. It’s called virtual because it provides an interface that doesn’t depend on the underlying OS.
   

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Java Interview Questions

Dear readers, these Java Interview Questions have been designed especially to get you acquainted with the nature of questions you may encounter during your interview for the subject of Java Programming Language. As per my experience, good interviewers hardly planned to ask any particular question during your interview, normally questions start with some basic concept of the subject and later they continue based on further discussion and what you answer:

Q: What do you know about Java?

A: Java is a high-level programming language originally developed by Sun Microsystems and released in 1995. Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX.

Q: What are the supported platforms by Java Programming Language?

A: Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX/Linux like HP-Unix, Sun Solaris, Redhat Linux, Ubuntu, CentOS, etc.

Q: List any five features of Java?

A: Some features include Object Oriented, Platform Independent, Robust, Interpreted, Multi-threaded

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115 Java Interview Questions and Answers – The ULTIMATE List

Object Oriented Programming (OOP)

Java is a computer programming language that is concurrent, class-based and object-oriented. The advantages of object oriented software development are shown below:

• Modular development of code, which leads to easy maintenance and modification.
• Reusability of code.
• Improved reliability and flexibility of code.
• Increased understanding of code.

Object-oriented programming contains many significant features, such as encapsulation, inheritance, polymorphism and abstraction. We analyze each feature separately in the following sections.

Encapsulation

Encapsulation provides objects with the ability to hide their internal characteristics and behavior. Each object provides a number of methods, which can be accessed by other objects and change its internal data. In Java, there are three access modifiers: public, private and protected. Each modifier imposes different access rights to other classes, either in the same or in external packages. Some of the advantages of using encapsulation are listed below:

• The internal state of every objected is protected by hiding its attributes.
• It increases usability and maintenance of code, because the behavior of an object can be independently changed or extended.
• It improves modularity by preventing objects to interact with each other, in an undesired way.

You can refer to our tutorial here for more details and examples on encapsulation.

Polymorphism

Polymorphism is the ability of programming languages to present the same interface for differing underlying data types. A polymorphic type is a type whose operations can also be applied to values of some other type.

Inheritance

Inheritance provides an object with the ability to acquire the fields and methods of another class, called base class. Inheritance provides re-usability of code and can be used to add additional features to an existing class, without modifying it.

Abstraction

Abstraction is the process of separating ideas from specific instances and thus, develop classes in terms of their own functionality, instead of their implementation details. Java supports the creation and existence of abstract classes that expose interfaces, without including the actual implementation of all methods. The abstraction technique aims to separate the implementation details of a class from its behavior.

Differences between Abstraction and Encapsulation

Abstraction and encapsulation are complementary concepts. On the one hand, abstraction focuses on the behavior of an object. On the other hand, encapsulation focuses on the implementation of an object’s behavior. Encapsulation is usually achieved by hiding information about the internal state of an object and thus, can be seen as a strategy used in order to provide abstraction.

General Questions about Java

1. What is JVM ? Why is Java called the “Platform Independent Programming Language” ? A Java virtual machine (JVM) is a process virtual machine that can execute Java bytecode. Each Java source file is compiled into a bytecode file, which is executed by the JVM. Java was designed to allow application programs to be built that could be run on any platform, without having to be rewritten or recompiled by the programmer for each separate platform. A Java virtual machine makes this possible, because it is aware of the specific instruction lengths and other particularities of the underlying hardware platform.
2. What is the Difference between JDK and JRE ? The Java Runtime Environment (JRE) is basically the Java Virtual Machine (JVM) where your Java programs are being executed. It also includes browser plugins for applet execution. The Java Development Kit (JDK) is the full featured Software Development Kit for Java, including the JRE, the compilers and tools (like JavaDoc, and Java Debugger), in order for a user to develop, compile and execute Java applications.
3. What does the “static” keyword mean ? Can you override private or static method in Java ? The static keyword denotes that a member variable or method can be accessed, without requiring an instantiation of the class to which it belongs. A user cannot override static methods in Java, because method overriding is based upon dynamic binding at runtime and static methods are statically binded at compile time. A static method is not associated with any instance of a class so the concept is not applicable.
4. Can you access non static variable in static context ? A static variable in Java belongs to its class and its value remains the same for all its instances. A static variable is initialized when the class is loaded by the JVM. If your code tries to access a non-static variable, without any instance, the compiler will complain, because those variables are not created yet and they are not associated with any instance.

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Java Basics - Interview Questions and Answers

1. What is the difference between a constructor and a method?

A constructor is a member function of a class that is used to create objects of that class. It has the same name as the class itself, has no return type, and is invoked using the new operator.
A method is an ordinary member function of a class. It has its own name, a return type (which may be void), and is invoked using the dot operator.

2. What is the purpose of garbage collection in Java, and when is it used?

The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources can be reclaimed and reused.
A Java object is subject to garbage collection when it becomes unreachable to the program in which it is used.

3. Describe synchronization in respect to multithreading.

With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources.
Without synchonization, it is possible for one thread to modify a shared variable while another thread is in the process of using or updating same shared variable. This usually leads to significant errors.

4. What is an abstract class?

Abstract class must be extended/subclassed (to be useful). It serves as a template. A class that is abstract may not be instantiated (ie. you may not call its constructor), abstract class may contain static data.
Any class with an abstract method is automatically abstract itself, and must be declared as such. A class may be declared abstract even if it has no abstract methods. This prevents it from being instantiated.

5. What is the difference between an Interface and an Abstract class?

An abstract class can have instance methods that implement a default behavior. An Interface can only declare constants and instance methods, but cannot implement default behavior and all methods are implicitly abstract.
An interface has all public members and no implementation. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.

6. Explain different way of using thread?

The thread could be implemented by using runnable interface or by inheriting from the Thread class. The former is more advantageous, 'cause when you are going for multiple inheritance, the only interface can help.

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