Download BOOK1_Introduction to Java 2017

Introduction to Java
What is Java and why do I need it?
 Java is a programming language and computing platform first
released by Sun Microsystems in 1995. Java is fast, secure,
and reliable. From laptops to datacenters, game consoles to
scientific supercomputers, cell phones to the Internet, Java is
everywhere!
 It is considered architecturally neutral, meaning that it can
run on any platform or operating system.
Where to Acquire Java
 Copy of Java can be obtained from www.java.com
 There are many different versions of Java. We will primarily be
working with an IDE (Integrated Development Environment)
called Ready to Program. Ready to Program is a very
streamlined, easy to use IDE, great for beginners. It does,
however, use an older version of Java. It allows for all of the
fundamental components of the language, including Object
Oriented Programming (OOP), and is sufficient for
everything you will need to learn here.
 Other, more sophisticated IDE’s, such as Eclipse, are also
available. These IDE’s will contain a newer version of Java,
however, the interface might be overwhelming for beginners.
 You can even use a simple editor, like NotePad, to write Java
programs.
Your First Java Program
Date: _____________
// The “HappyBirthday” class.
public class HappyBirthday
{
public static void main (String[ ] args)
{
System.out.println(“Happy Birthday!”); // Display
message
} // main method
} // HappyBirthday class
What does it all mean?
Line




1 - // The “HappyBirthday” class.
Comment line
Comments begin with // ;
Any commented line is ignored by the computer
Longer or block comments are enclosed with /* and */
Line 2 - public class HappyBirthday
 Defines the class name *starts with a capital, no spaces
 Class name must agree with the file name; in this case, we
save the code as: HappyBirthday.java
**Case
sensitive!
Line



3-{
Opening brace
Defines the start of the class
Class is closed in line 8 with a closing brace and a comment:
} // HappyBirthday class
Lines 4 to 7
 Method defined inside the class braces
 Our example shows just one method
Line 4
 Main method starts with line: public static void main (String[ ]
args)
o This is a required method that starts the program
o All code within the {} of this method is executed by the
computer
Additional Points
 All Java programming statements end with a semicolon
 The contents of all classes are contained within opening and
closing braces
 A series of characters in double quotes is called a literal string
 All Java applications must have a method named main()
 The statement System.out.print() will display output data and
remain on the same line.
 The statement System.out.println() will display a line of output
and advance to the next line.
Using Keyboard Input
Date: _____________
Let’s examine the “HappyBirthday” program one more time.
Wouldn’t it be better to display the entire song for a specific
person? Maybe the name of the birthday girl/boy can be entered
through the keyboard and then used in the song. To do this:
1. Make available the Java input/output routines.
 Done through import statements that happen before the
class is defined
 For keyboard input, the following statement must be added:
import java.io.*;
2. Modify the main method to handle keyboard errors.
 Using keyboard or disk access means there is a possibility
that an error could occur (called an exception)
 The statement: throws IOException must be added to the
definition line of the main method
3. Define the input stream reader which allows information to
come from the keyboard.
 Input and output is handled in streams of characters
 To create an input stream reader object:
BufferedReader keyboardInput=new BufferedReader
(new InputStreamReader (System.in));
- object is named keyboardInput for “the data entered in on
the keyboard”
4. Create an object or a variable to hold the information that
comes in from the keyboard.
String birthdayName; //This creates a storage box called //birthdayName
that can be used to hold the typed information
5. Now use the keyboard input command
 First prompt the user to enter a name using a print or
println command
 Then, get the input
System.out.print (“Please enter your name: ”);
birthdayName = keyboardInput.readLine ();
birthdayName will be assigned whatever the user enters on
the keyboard.
The entire program is shown below:
import java.io.*;
// The “Happy Birthday” class.
public class HappyBirthday
{
public static void main (String[ ] args) throws IOException
{
BufferedReader keyboardInput=new
BufferedReader (new InputStreamReader (System.in));
String birthdayName;
//Ask user for name
System.out.print (“Please enter your name: ”);
birthdayName = keyboardInput.readLine ();
//Display the birthday song with the name
System.out.println(“Happy Birthday to you”);
System.out.println(“Happy Birthday to you”);
System.out.println(“Happy Birthday dear ” + birthdayName);
System.out.println(“Happy Birthday to you”);
} // main method
} // HappyBirthday class
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