Session 5 Programming Languages

Transcription

1 Information Technology Essentials Session 5 Programming Languages Copyright 2005 Thomas Malone, Stuart Madnick Acknowledgments: Slides marked SM are adapted from Stuart Madnick, MIT.

2 Outline Types of software Types of programming languages Examples Java Y2K

3 Types of software System software Operating systems Programming languages Database systems Application software General office tasks (word processing, etc.) Accounting Design Factory automation

4 Programming languages Machine language Assembly language High-level languages Fourth-generation languages

5 A sample LMC program INSTRUCTIONS opcode 000 1xx 2xx 3xx 5xx symbolic stop add subtract store load get put 1 ASSEMBLY LANG (Source Program) STEP INSTRUCTION 00 get 01 store w 02 get 03 store b 04 load w 05 add b 06 put 07 stop 2 MACHINE LANG. (Object Program) LOC INSTRUCTION Source: S. Madnick, MIT

6 Machine language Binary Machine dependent Stored in the computer when the program is running Example:

7 Assembly language Mnemonic Symbolic addressing One-to-one correspondence with machine language Example: Get X Add Y Store Z

8 Automatically translating assembly language to machine language Get X Add Y Store Z... Assembler Assembly language program ( source code ) Machine language program ( object code )

9 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

10 High-level languages - Examples Fortran Basic Visual Basic C C++ Java

11 Example 1 Basic L Q F L O Q F X L G O F X H O X R V W L R O X R O U D P V H K G Q F X O R Q G O V L I O Y Q 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 Q F X O R V W L R O X R O U D P V H O X D O??? O X V O Q F H Q K X O X R O F H O V J O H X Q F X G W I Z K V W F X O Z Q F X O G O F X O O F W I P Q F W X O F W I P H V O Y R Q O F W I P 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 R O F ' X O F W I P Q F W X O F W I P V V L Z G W I + K V W F X Q F X O R O L O V J O X R O F W I P O Q G L F H! X E X E E O E X E2O

12 Example 2 C O L Q F L O Q F X L G O F X H O X R V W L R O X R O U D P V H ( 5 *$ 9 / O ` 5 0 : ) 8. <, <. 5 *O 1 O 3O 9 0. ) O. 8. ; 2 5 *) */ < 8 O $ 0 / *) 8 O Z O 2O O 5 *) : / < O Z O 2 $ 0 / ) ` ` O X R Q G O V L I O Y Q 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 $ 0 / ) ` ` O X R V W L R O X R O U D P 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 $ 0 / ) ` ` O G O F X O O F W I P E2 $ 5 * O */ < 8 2, 5 9 O 1 */ < 8 O % Z??? 3 & & : / < O Z : / < O O < 8 $ 0 / 8 $ 0 / ) ` ` O G F X O X R O F ' X O F W I P $ 5 < 8 */ 2 *) 2 * E2 * */ ; O Z O : / < O + O $ 0 / 8 $ 0 / ) ` ` O R L O V J O X R O F W I P G O Q G O ` O. 8. ; *) 2 *X ` 2

13 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.."); } }

14 Automatically translating high-level language to machine language Z = X + Y... Compiler High-level language program ( source code ) Machine language program ( object code )

15 Interpreting high level languages Z = X + Y... Interpreter High-level language program ( source code )

16 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

17 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?

18 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

19 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: $ Open Deposit Withdrawal Joe s checking account Owner: Joe Balance: $400 Minimum balance: $ Open Deposit Withdrawal

20 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

21 Java Operation Servers Sun/ UNIX Internet S J D Windows 2000 Mac OS Static pages (S) Dynamic pages (D) Java applets (J) HTML page Java applet HTML page Java applet } same Windows XP HTML Interpreter Netscape ( Win 2000) Netscape ( Mac OS) Windows 2000 OS Mac OS PC Hardware Java interpreter HTML Interpreter Client environments Java interpreter PowerMac Hardware } different SM

22 SM Java reality check Highly interactive or too slow (interpretive) Nice programming language or too limited Secure environment or (1) not secure enough or (2) too secure (restrictive) Portable only if consistent Java interpreter availabl (Java dialects )

23 What will happen with Java?

24 Y2K problem Why was this a hard problem? Was money wasted?