Exercise 9.1: Class And Object

Introduction:

In this exercise, you will exercise the concept object creation using new keyword. We will learn how you are going to create your own Class in the next session.

* If you are new to Object-Oriented Programming concept, please read "Object Oriented Programming Concept" section of the Java Programming Tutorial.


Steps to follow:

1. Write ClassAndObject.java. (You are welcome to do this work using either command line tools or NetBeans. The instruction here is given using command line tools. In general, using NetBeans is highly recommended.) Please make sure you read the comments.

* cd \myjavaprograms
* jedit ClassAndObject.java


public class ClassAndObject {

public static void main( String[] args ){

// Create an instance of a class by using a Java language keyword "new".
// For example, in order to create an object instance of a String class,
// you will do the following
String strInstance1 = new String ("I am object instance of a String class");
System.out.println("value of strIntance1 = " + strInstance1);

// String class a special class for which you can create an instance
// of it by assigning a string literal. No other class allows this form of object creation.
String strInstance2 = "I am object instance of a String class";
System.out.println("value of strIntance2 = " + strInstance2);

// Create an object instance of Integer class
Integer intInstance1 = new Integer (20);
System.out.println("value of inIntance1 = " + intInstance1);

}

}
Code 9.1: ClassAndObject

2. Compile and run the code

* javac ClassAndObject.java
* java -classpath . ClassAndObject

3. Verify the result is as following

* C:\myjavaprograms>java -classpath . ClassAndObject
value of strIntance1 = I am object instance of a String class
value of strIntance2 = I am object instance of a String class
value of inIntance1 = 20


Homework:

1. Modify ClassAndObject.java as following, compile and run the code

* Create another object instance of String class using new keyword. Initialize it with the following value. Display it using Sytem.out.println(..) method.
o "I am another object instance of String class"