Yashwanth Sagar

Java has a wide range of applications ranging from handheld devices to web applications. Advanced Java (a name used in contrast to Java 2 Enterprise Edition) can be used to develop Enterprise applications. Those applications that are dynamic and can run on wide range of devices like computers, mobile phones, etc. In here, you would be learning to program the front-end and the back-end of a system's architecture, and also learn how to connect the both using the concepts of JDBC. Any more queries, you can contact me. 24X7 available to help you.

To understand 'transient' you must first understand serialization. Serialization is the process of making the object’s state persistent. That means the state of the object is converted into stream of bytes and stored in a file. In the same way we can use the de-serialization concept to bring back the object’s state from bytes. This is one of the important concept in Java programming because this serialization is mostly used in the networking programming. The object’s which are needed to be transmitted through network have to be converted into bytes and for that purpose every class or interface must implement 'Serializable' interface. It is a marker interface without any methods. The keyword 'transient' in Java is used to indicate that the variable shouldn't be serialized. By default all the variables of a class that implements Serializable are in persistent state. In some cases, you may want to avoid persisting some variables because you don’t have the necessity to transfer across the network. So, you can declare those variables as transient. If the variable is declared as transient, then it will not be persistent.

Consider this: class ThisDemo { int a,b,c; public ThisDemo(int a, int b) { this.a=a; //this.a means the class's instance variable. simple 'a' means the parameter this.b=b; } public void sum() { c=a+b; System.out.println("Sum="+c); } } Now, in this class, there are a few instance variables (a,b,c), a constructor, and a method sum(). The constructor, as we know can be used to initialize the instance variables on a class. If you'd notice, it is a parameterised constructor, and the parameters have the same names as that of instance variables. To initialize the instance variables of the class, you'd certainly want to refer them in the constructor. But you can't write a=a and b=b, coz that doesn't make sense. 'a' & 'b' inside the constructor means the parameters of the constructor. 'this' keyword comes in handy here. If you want to refer to the instance variables of the class, then you can use the 'this' keyword when the instance variable names and the parameter names of a method/constructor are same.

This is done in case of Abstract Classes. An Abstract Class is something that hides some implementations (method details). Suppose, for example, you would like to create a class that tells what an object will do without specifying how the object does that, letting it for the child classes to provide their implementations to this method accordingly, you'd mark the class as abstract, extend it's properties to a derived class, and in the derived class, provide the implementations for the abstract methods provided in the abstract base class. An abstract method, in contrast, is a method that does not have any details. it can be something like this: abstract class BaseClass { public abstract void methodName1(); //an abstract method to be defined in child class } public class ChildClass extends BaseClass { public void methodName1() { ------------ ------------ } } The child class which extends an abstract base class must implement all the abstract methods that are provided in the abstract base class. And the most important point with the abstract classes is that you cannot instantiate them. For the above example: BaseClass obj=new BaseClass(); //is absolutely illegal. Hence, abstract classes must be instantiated by using their derived class constructors. So we write this statement: BaseClass obj=new ChildClass(); //legal.