15.561
Information Technology Essentials
Session 5
Programming Languages
Copyright © 2005 Thomas Malone, Stuart Madnick
Acknowledgments:
Slides marked “SM” are adapted from Stuart Madnick, MIT.
Outline
• Types of software
• Types of programming languages
• Examples
– Java
– Y2K
Types of software
• System software
– Operating systems
– Programming languages
– Database systems
• Application software
–
–
–
–
–
General office tasks (word processing, etc.)
Accounting
Design
Factory automation
…
Programming languages
• Machine language
• Assembly language
• High-level languages
• Fourth-generation languages
A sample LMC program
1
INSTRUCTIONS
opcode
symbolic
000
1xx
2xx
3xx
5xx
901
902
stop
add
subtract
store
load
get
put
ASSEMBLY LANG
(Source Program)
2
MACHINE LANG.
(Object Program)
STEP
INSTRUCTION
LOC
INSTRUCTION
00
01
02
03
04
05
06
07
get
store w
get
store b
load w
add b
put
stop
00
01
02
03
04
05
06
07
901
398
901
399
598
199
902
000
Source: S. Madnick, MIT
Machine language
• Binary
• Machine dependent
• Stored in the computer when the program is running
• Example:
01110110001010010010 ….
Assembly language
• Mnemonic
• Symbolic addressing
• One-to-one correspondence with machine language
• Example:
Get X
Add Y
Store Z
Automatically translating assembly
language to machine language
Get X
Add Y
Store Z
...
Assembly
language
program
(“source code”)
Assembler
11001000100
01100100011
10001011001
...
Machine
language
program
(“object code”)
High-level languages
• Closer to how people think about their problems
• No one-to-one correspondence to machine language
• General purpose
• Example:
Z=X+Y
High-level languages - Examples
• Fortran
• Basic
• Visual Basic
•C
• C++
• Java
Example 1 – Basic
!
K
G
K
QF
H
L QF L OQF X L G O F X
G
Q F X O �X R Q G O V L I O Y Q Q F X O �X R V W L R O X R O U D P
QF X
W I Z V W F X OZ Q F X O � G O F X O O F W
W X OF W I P V O Y R Q O F W I P O ` O ? ? ?
G W I Z G W I � F W I P K V W F X Z K V W F X � 6
Q F X O � G O F X O X
QF W X OF W I P V V L Z G W I +K V W F X Q F X O �X R O L O V J O X R
F H
H OX R V W L R OX R OU D P V
H
OJ QF H OX R O L OV J OQF X L G OD V W O F X E
V H OX D O? ? ? OX V OQF H QK X OX R O F H OV J OH X E
I P E
R OF ' X OF W I P E
O F W I P O Q G E2O L Example 2 – C++
++O L QF L OQF X L G O F X H OX R V W L R OX R OU D P V
( 5 *$ 9 / � � O ` 5 0 : ) 8 � . < , < . 5 *O 1 O 3O
90 . )O. � 8 . ; � 2
5 *) */ < � 8 � O $ 0 / *) � 8 O Z O 2O O 5 *) : / <
$ 0 / ) ` ` O �X R Q G O V L I O Y Q $ 0 / ) ` ` O �X R V W L R O X R O U D P
$ 0 / ) ` ` O � G O F X O O F W
$ 5 * O */ < � 8 2
, 5 9 � O 1 */ < � 8 O % Z ? ? ? 3
&
&
: / <
$ 0 /
$ 0 /
$ 5*
H
OZ O 2
O J Q F H O X R O L O V J O Q F X L G O D V W O F X O *E2
V H O X D O ? ? ? O X V O Q F H Q K X O F H O V J O H X O *E2
I P E2
O Z : / < O � O */ < � 8 2
*) � 8 � � 2
) ` ` O �* G F X O X R O F ' X O F W I P E2
*/ < � 8 2
. � 8 . ; � O Z O : / < O + O $ 0 / *) � 8 2
$ 0 / ) ` ` O �*X R L O V J O X R O F W I P G O Q G O �` ` O . � 8 . ; � 2
Example 3 – Java
{
import java.io.*;
import java.lang.*;
/**
** Prompts user for list of numbers and outputs average
**/
class AverageNumbers {
public static void main (String[] args) {
float sum = 0;
float average = 0;
int counter = 0;
System.out.println("THIS PROGRAM WILL FIND THE
AVERAGE OF THE INTEGERS YOU ENTER
THROUGH THE KEYBOARD. TYPE 999 TO
INDICATE END OF DATA.");
try
}
}
BufferedReader in = new BufferedReader(new
InputStreamReader(System.in));
String cin = "0";
System.out.println("Please enter a number.");
while (!(cin=in.readLine()).equals("999"))
{
sum = sum + Integer.parseInt(cin);
counter = counter + 1;
System.out.println("Please enter another
number.");
}
in.close();
average = sum/counter;
System.out.println("The average of the numbers is :
"+average);
}
catch (IOException e)
{
System.out.println("Ooops..");
}
Automatically translating high-level
language to machine language
Z=X+Y
...
High-level
language
program
(“source code”)
Compiler
11001000100
01100100011
10001011001
...
Machine
language
program
(“object code”)
“Interpreting” high level languages
Z=X+Y
...
High-level
language
program
(“source code”)
Interpreter
Interpreting high level languages
• Advantages
– Can give machine independence
» (e.g., one machine can “look” like another)
– Can be easier to debug and modify
– Can give more flexibility at “run time”
• Disadvantages
– Slower
“Fourth-generation” languages
• Even closer to how people think about their problems
• Special purpose
• Examples:
– Scripting languages
» FIND ALL RECORDS WHERE NAME IS “SMITH”
– Spreadsheet formulas?
Object-oriented programming
• A special kind of high-level language
• Can increase programming efficiency and software
re-use
• Combines procedures and data into “objects”
• Arranges objects in “class hierarchies”
• “Inherits” properties of objects in this hierarchy
Class inheritance in
object-oriented programming
Bank account
Owner
Balance
----­
Open
Deposit
Withdrawal
Credit card account
Owner
Balance
Credit limit
----­
Open
Deposit
Withdrawal
Authorize charge
Checking account
Owner
Balance
Minimum balance: $100
----­
Open
Deposit
Withdrawal
Joe’s checking account
Owner: Joe
Balance: $400
Minimum balance: $100
----­
Open
Deposit
Withdrawal
What’s good about Java?
• Highly interactive
– Traditional Web - application software runs on server
– Java applets dynamically downloaded and run on client
(e.g., input data validation)
• “Nice” programming language
– Simpler than C/C++
– Object-oriented
• Secure programming environment
– “Sandbox” approach
• Portable (“write once, run anywhere”)
– Based on Java byte-code interpreter
SM
Java Operation
Servers
S
Internet
Sun/UNIX
Windows 2000
Windows XP
D
J
• Static pages (S)
• Dynamic pages (D)
• Java applets (J)
Mac OS
HTML
page
Java
applet
HTML
page
Java
applet
HTML
Interpreter
Java
interpreter
HTML
Interpreter
Java
interpreter
Netscape (Win 2000)
Netscape (Mac OS)
Windows 2000 OS
Mac OS
PC Hardware
PowerMac Hardware
Client environments
}
same
}
different
SM
Java reality check
• Highly interactive
or too slow (interpretive)
• “Nice” programming language
• Secure environment
• Portable
or too limited
or (1) not secure enough or
(2) too secure (restrictive)
only if consistent Java interpreter availabl
(Java “dialects”)
SM
What will happen with Java?
Y2K problem
• Why was this a hard problem?
• Was money wasted?