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How to install JDK and SET Environment setup for run a java program.

Hy dear are you worrying  about setup of java environment .So please following some steps   and start programming .

Java SET UP  is freely available on the oracle site. 
http://www.oracle.com/technetwork/java/javase/downloads/index.html?ssSourceSiteId=otnjp

So you download a version based on your operating system.

Follow all the instruction and installed the .exe file.

Once you installed Java on your machine,you would need to set environment variables to point to correct installation directories:

Check your JDK before set the path. 

Assuming you have installed Java in

C:\Program Files\java\jdk

           or

C:\Program Files (x86)\Java\jdk1.5.0_09

directory:

Now the start the process of set the path.

Right-click on “My Computer” and select “Properties”.

Click on “advanced system setting” you get a new window.

Click on the 'Environment variables' button under the 'Advanced' tab.

Click  new .

  

Now, copy the path from where you installed “java.exe” file .

Assuming you have installed Java in C drive.

So path is    C:\Program Files (x86)\Java\jdk1.5.0_09\bin

Value name     : -         PATH

Variable value :-     C:\Program Files (x86)\Java\jdk1.5.0_09\bin

Now Click on OK and open the CMD.

and type javac than enter.

If you will get this your path is set successfully.

To write your Java programs, you will need a text editor. for now, you can consider one of the following:-

   Notepad: On Windows machine you can use any simple text editor like Notepad.

    Netbeans: is a Java IDE that is open-source.
https://netbeans.org/downloads/


    Eclipse: is also a Java IDE developed by the eclipse open-source community.
https://www.eclipse.org/downloads/

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Basic Polymorphism in java

The word "polymorphism" means "many forms". It comes from Greek word "poly" (means many) and "morphos" (means form). For examples, in chemistry, carbon exhibits polymorphism because it can be found in more than one form: graphite and diamond. Each of the form has it own distinct properties.
A subclass possesses all the attributes and operations of its superclass (because a subclass inherited all attributes and operations from its superclass). This means that a subclass object can do whatever its superclass can do. As a result, we can substitute a subclass instance when a superclass instance is expected, and everything shall work fine. This is called substitutability.
In our earlier example of Circle and Cylinder: Cylinder is a subclass of Circle. We can say that Cylinder "is-a" Circle (actually, it "is-more-than-a" Circle). Subclass-superclass exhibits a so called "is-a" relationship.
Via substitutability, we can create an instance of Cylinder, and assign it to a Circle (its superclass) reference, as follows:

// Substitute a subclass instance to its superclass reference
Circle c1 = new Cylinder(5.0);

You can invoke all the methods defined in the Circle class for the reference c1, (which is actually holding a Cylinder object), e.g. c1.getRadius() and c1.getColor(). This is because a subclass instance possesses all the properties of its superclass.
However, you cannot invoke methods defined in the Cylinder class for the reference c1, e.g. c1.getHeight() and c1.getVolume(). This is because c1 is a reference to the Circle class, which does not know about methods defined in the subclass Cylinder.
c1 is a reference to the Circle class, but holds an object of its subclass Cylinder. The reference c1, however, retains its internal identity. In our example, the subclass Cylinder overrides methods getArea() and toString(). c1.getArea() or c1.toString() invokes the overridden version defined in the subclass Cylinder, instead of the version defined in Circle. This is because c1 is in fact holding a Cylinder object internally.

Summary

1. A subclass instance can be assigned (substituted) to a superclass' reference.
2. Once substituted, we can invoke methods defined in the superclass; we cannot invoke methods defined in the subclass.
3. However, if the subclass overrides inherited methods from the superclass, the subclass (overridden) versions will be invoked.

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