Download Java & Dr. Java

Java
Java
• A programming language specifies the words and
symbols that we can use to write a program
– Syntax: A programming language employs a set of rules that
dictate how the words and symbols can be put together to form
valid program statements
– The Java programming language was created by Sun
Microsystems, Inc.
– It was introduced in 1995 and it's popularity has grown quickly
since
– Java is an object-oriented programming language
Java
• In the Java programming language, all source code is
first written in plain text files ending with the .java
extension. – We will use DrJava text editor for our
IDE.
• Those source files are then compiled into .class files
by the javac compiler. – It will compile to run on any
machine. It is said to be neutral.
• A .class file contains bytecodes — the machine
language of the Java Virtual Machine (Java VM).
• The source code must be compiled to bytecode.
Java Virtual Machine
• Because the Java VM is
available on many
different operating
systems, the same .class
files are capable of
running on Microsoft
Windows, the Solaris TM
Operating System
(Solaris OS), Linux, or
Mac OS.
• This makes Java platform
neutral.
How to type the Java source code
• Through an editor or IDE (Integrated Development
Environment.)
• Editor will generally highlight the Java syntax, indent for
you, balance your parentheses and braces, and let you
compile from within the editor.
• IDEs have visual Java development tools, tight
integration with the compiler or application server, and
may include tools for debugging, refactoring, version
control, and so forth. We will use Dr. Java as our IDE.
What is DrJava?
• DrJava is a free
integrated development
environment for doing
Java programming
– From Rice University
– It is written in Java
• It has several window
panes in it
– For creating programs
(definitions pane)
– For trying out Java code
(interactions pane)
– Listing of open files (files
pane)
Dr. Java
Files
Pane –
List the
open
files in
Dr.
Java
Definitions pane – This is where you write your classes.
Simply a text editor.
You compile all current files open in the files pane b y clicking
on the compile all
Interactions Pane – You can type commands and it will
execute but not save.
Java Program Structure
• In the Java programming language:
– A program is made up of one or more
classes Every program typed is in a
class.
Class – blueprint for creating objects that
have properties and methods.
The Java Application Programming
Interface (API )
• The API is a large collection of ready-made
software components that provide many useful
capabilities.
• It is grouped into libraries of related classes and
interfaces; these libraries are known as
packages.
What Is a Package?
• A package is a namespace that organizes a set of
related classes and interfaces.
• What is a class: A class is a generic template for a
set of objects with similar features. All the GUI tools
we will use are in a class called javax.swing.
• The Java platform provides an enormous class library (a
set of packages) suitable for use in your own
applications. This library is known as the "Application
Programming Interface",
• http://java.sun.com/javase/6/docs/api/index.html
Java Program Structure
//
comments about the class
public class MyProgram
{
All classes begin
and end with a
curly brace
class header
class body
Comments can be placed almost anywhere
}
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Java Program Structure
//
comments about the class
public class MyProgram
{
//
comments about the method
public static void main (String[] args)
{
method body
method header
}
}
All methods begin and end
with a curly brace
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Main method
public static void main(String[]args)
{
// program statements to print and execute
}
Saving a File
• You must save the java file with the
same name as the class name.
It will save it with a .java extension.
The command to execute a compiled Java
application in run.
Comments
• Comments in a program are called inline documentation
• They should be included to explain the purpose of the
program and describe processing steps
• They do not affect how a program works
• Java comments can take three forms:
// this is a single line comment
/* this is a multi-line comment that will
* take more than one line
**/
/** this is a javadoc comment. Used by
Programs for documentation.
*/
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Identifiers
• Identifiers are the words a programmer uses
in a program. Can be reserved words Java has
created or variables the programmer creates.
• Rules for identifiers:
– An identifier can be made up of letters, digits, the underscore
character ( _ ), and the dollar sign
– Identifiers cannot begin with a digit
– Java is case sensitive - Total, total, and TOTAL are
different identifiers
– By convention, Java programmers use different case styles for
different types of identifiers, such as
• title case for class names - Lincoln
• upper case for constants - MAXIMUM
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Reserved Words
•
The Java reserved words: these are words Java has pre-defined for a
special purpose. You cannot create a variable, class name or method
name with these words.
abstract
assert
boolean
break
byte
case
catch
char
class
const
continue
default
do
double
else
enum
extends
false
final
finally
float
for
goto
if
implements
import
instanceof
int
interface
long
native
new
null
package
private
protected
public
return
short
static
strictfp
super
switch
synchronized
this
throw
throws
transient
true
try
void
volatile
while
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White Space
• Spaces, blank lines, and tabs are called white
space
• White space is used to separate words and
symbols in a program
• Extra white space is ignored
• A valid Java program can be formatted in many
ways
• Programs should be formatted to enhance
readability, using consistent indentation
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There are 8 Primitive data types in Java.
Data type tells the kind of information that will be stored in memory.
TYPE
What it hold
RANGE
byte
Whole number
8 bits -128 to 127
short
Whole number
16 bits
-32768 to 32767
int
whole numbers
32 bits -2 billion to 2 billion
long
Whole number
64 bits -big to +big
float
Fractional
number
32 bits -big to +big
double
fractional
number
64 bits -1.7E+308 to 1.7E+308
char
‘A’
One character
16-bit
One character
boolean
True or false
value
Holds two values: {true, false}
Object
• Objects are made
from the class they
belong to. You can
create several
objects from a class
– like a cookie cutter.
JOptionPane jp = new JOptionPane();
Class
Variable
name
New object created
Turtle
Object 1
Turtle
Object 2
Turtle: Class
Objects
Objects - instance of a class.
Objects have attribute or state
A state is a property or something the
object knows about itself.
Turtle - size, color, name, age
Objects
• Objects have methods / Behavior /
Actions
• Things it knows how to do.
Turtle turn, turnRight, turnLeft, forward
Argument / Parameter
• Parameter is extra information required to
the object or method.
Turtle tom(130, earth);
Parameter – the
information inside is
called arguments
They always appear in
parenthesis.
It is required so the Turtle will know where he is in the world and what world
to be in.
Variables – stores value in a
memory location
Programming uses variables.
•
You need to learn this!
Declare is to tell what type of data the variable will hold and its name
int number;
double money;
boolean done;
You cannot use a variable until you declare the type
•
Initialize is to assign the variable a value using the = sign
int number = 37;
double money = 28.42;
boolean done = true;
Statements
• Statements in Java are commands.
• All statements end in a semicolon
Constants
• Constants are variables that once
assigned cannot change. They are
identified by using the final and capitalizing
the variable name.
final int SALARY;
Assignment Operator
• The = sign is the assignment operator for
variables.
int num = 2;
boolean done = true;
double average = 4.5;
Arithmetic Statements
45 /2
45 and 2 are called operand.
er
Operators are:
+, - , * , / , %
Addition, substraction, multiplication, and
modulus (remainder operator).
System Class
Basic print statement in Java
System.out.println(“This will print”);
class
object
method
System is a class.
out is the object created from the System class
println is the method from the System class that allows it to print.
A period separates classes, objects and methods.
Print and Println Methods
•
•
•
•
•
//********************************************************************
// Countdown.java
Author: Lewis/Loftus/Cocking
//
// Demonstrates the difference between print and println.
//********************************************************************
•
•
•
•
•
•
•
•
•
•
•
public class Countdown
{
//----------------------------------------------------------------// Prints two lines of output representing a rocket countdown.
//----------------------------------------------------------------public static void main (String[] args)
{
System.out.print ("Three... ");
System.out.print ("Two... ");
System.out.print ("One... ");
System.out.print ("Zero... ");
•
•
•
•
System.out.println ("Liftoff!"); // appears on first output line
System.out.println ("Houston, we have a problem.");
}
}
Three…Two…One…Zero…Liftoff!
Houston, we have a problem.
What will this program
output look like
String Literals
• The part inside the “ double quotes “ is
called a String Literal.
• Concatenation: Add one String to
another using the + sign.
• “ “ makes a space
• System.out.println(“This is a String” + “ “
+ “and this is another one.”);
Control Structures
• There are 3 basic control structures in
Java
• Sequential Flow - Everything in order
• Conditional or selection: if statements that
make a decision
• Iteration: Loop or a repeated instruction