Download programming language

Chapter 1
Programming Languages
Application Development: Top 10
Programming Languages to Keep You
Employed
1. Java
2. C#
3. C++
4. JavaScript
5. Visual Basic
6. Php
7. Objective C
8. Peral
9. Python
10. Ruby
If you want to make money in programming
what are the best languages to learn?
What do you think are the top
programming languages?
http://www.eweek.com/c/a/ApplicationDevelopment/Top-10-ProgrammingLanguages-to-Keep-You-Employed719257/
Where is Java?
Where is Java?
Java Life Video
What is Java technology and
why do I need it?
• Java is a programming language and computing
platform first released by Sun Microsystems in
1995. Sun Microsystems was acquired by
Oracle.
• It is the underlying technology that powers stateof-the-art programs including utilities, games, and
business applications.
• Java runs on more than 850 million personal
computers worldwide, and on billions of devices
worldwide, including mobile and TV devices.
Where is Java?
• 1.1 billion desktops run Java
• 930 million Java Runtime Environment downloads
each year
• 3 billion mobile phones run Java
• 31 times more Java phones ship every year than
Apple and Android combined
• 100% of all Blu-ray players run Java
• 1.4 billion Java Cards are manufactured each year
• Java powers set-top boxes, printers, Web cams,
games, car navigation systems, lottery terminals,
medical devices, parking payment stations, and more.
Programming Language Levels
• Different Programming language levels:
1. machine language 1s and 0s (What the computer
understands – binary code)
2. assembly language - low level step above machine.
Still hard to code and understand.
3. high-level language – use English words for code.
Easy to use.
•
Each type of CPU has its own specific machine language that interprets the
1s and 0s.
•
The other levels were created to make it easier for a human being to read
and write programs so we can use English words to code. 1s and 0s were
too hard!
8
Programming Languages
• A program must be translated into machine language
before it can be executed on a particular type of CPU
• This can be accomplished in several ways
• A compiler is a software tool which translates source
code into a specific target language
• Often, that target language is the machine language for
a particular CPU type
9
Java is Unique
• The Java compiler translates Java source code into a
special representation called bytecode
• Java bytecode is not the machine language for a
particular CPU.
• Therefore the Java compiler is not tied to any particular
machine or platform.
• An interpreter then coverts the bytecode to the language
the machine understands.
• Therefore, Java is considered to be architecture-neutral
and can run on PCs, Macs, Linux, anywhere.
10
IDE
• Programming languages must have a text editor called an
Integrated Development Environment used to type the
source code for the program.
• There are many integrated development environments for writing
code.
–
–
–
–
–
–
–
Sun NetBeans
Borland JBuilder
MetroWerks CodeWarrior
Microsoft Visual J++
IBM Eclipse
Monash BlueJ
Dr. Java
How does it
work
Steps:
1. Write a program using an IDE in Java source
code.
2. Compile it (Java has a compiler which will convert
it to bytecode which is platform independent.)
3. An interpreter then converts it to 1s and 0s for the
platform it is on. (when we hit run)
When you write, compile and run you have 3 files.
Source file, java file, class file. Only the source file
will open. The others are for execution by the
compiler and interpreter.
When we download
Java, we don’t see it. It
is a considered a virtual
machine. To
communicate we use an
integrated development
environment (in our case
Dr. Java) which is a text
editor where we type our
code.
Our code has to
converted to 1s and 0s.
Java has a compiler that
converts code to
bytecode. This is why it
can be used on any
platform (windows, linux,
mac). Then the
interpreter will convert it
to the 1s and 0s for that
particular platform.
Summary for IDE
• Integrated Development Environment is used
to type java source code. It contains an
editor, compiler and an interpreter and
debugger in one package.
• The source code is compiled (by a compiler)
into code called bytecode.
• A java interpreter converts the bytecode into
instructions for that particular CPU.
Dr. Java as our IDE
• Dr. Java is a simple editor tool for entering
program text and interaction space so that
you can try things out in Dr. Java and
crate new programs.
• Free under the DrJava Open Source
License.
DrJava Features
• Works with multiple
files
– Files pane
Files
pane
• Color coded editor
– Definitions pane
• Interpretation of
Java code
– Interactions pane
• Integrated debugger
Interactions pane
Definitions pane
How to use the console pane
• If you click on the
console tab
– You will see the
console pane
• It shows just the
items that you have
printed to the
console
– Using
System.out.println or
– System.out.print
Open 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
• A programming language specifies the words and
symbols that we can use to write a program called
Syntax
Java Program Structure
• In the Java programming language:
– A program is made up of one or more classes
– A class contains one or more methods
– A method contains program statements
• These terms will be explored in detail throughout the
course
• A Java application always contains a method called
main
• See Lincoln.java (page 27)
Java Program Structure
//
comments about the class
public class MyProgram
{
class header
class body
Comments can be placed almost anywhere
}
20
Java Program Structure
//
comments about the class
public class MyProgram
{
//
comments about the method
public static void main (String[] args)
{
method body
method header
}
}
21
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:
They do not want you to use comments on your AP Exam
// this comment runs to the end of the line
/*
this comment runs to the terminating
symbol, even across line breaks
/** this is a javadoc
comment
*/
*/
22
Identifiers – Identify yourself!
• Identifiers are the words a programmer uses in a program. Java
looks for those words.
• An identifier can be made up of letters, digits, the underscore
character ( _ ), and the dollar sign
• Identifiers cannot begin with a digit. They can only begin with an _
or a letter.
• 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 (things that won’t change)- MAXIMUM
23
Reserved words as Identifiers
• Sometimes we choose identifiers ourselves when writing
a program (such as Lincoln)
• Sometimes we are using identifiers Java has created for
special purposes. Those have special meaning so we
can’t use those for our identifiers that we create.
• The identifiers reserved by Java are associated with
methods and data created by Java that we don’t have to
know about. (encapsulation). We just use them and
they work.
Reserved Words
• The Java reserved 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
25
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
• See Lincoln2.java (page 33)
• See Lincoln3.java (page 34)
26
Syntax and Semantics
• The syntax rules of a language define how we can put
together symbols, reserved words, and identifiers to
make a valid program
• The semantics of a program statement define what that
statement means (its purpose or role in a program)
• A program that is syntactically correct is not necessarily
logically (semantically) correct
• A program will always do what we tell it to do, not what
we meant to tell it to do
27
Errors could be syntax or
semantic
• Syntax – rules of a language
– Java will not compile programs with syntax errors
• Semantics – How the program is put together.
What will happen when it is executed.
– Java will compile and run but results will not be
correct.
Three kind of errors
• Compile time error – syntax error. Will not
compile the program. Wrong syntax
• Runtime error – Will compile but will not
run. It crashes during execution. Try to
divide by 0 or index outbound in arrays
• Logical error – Will compile, Will run and
print but produces the wrong output.
(program is not put together correctly).
Used wrong equation or steps in solving
the solution.