9/1/2006 CMSC 131 Fall 2006Rance Cleaveland©2006 Univeristy of MarylandLecture 2: ProgrammingLast time:1. Course information2. Computer basicsToday:1. Programming languages2. Eclipse and CVSCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland1Programming Languages Used to write programs that run on computers Generations of programming languages 1st(1GL): machine code 2nd(2GL): assembly code 3rd(3GL): procedural languages 4th(4GL): application-specific languages 5th(5GL): constraint languagesCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland21stGeneration: Machine Code Recall: computer data is 0’s and 1’s. In machine code, so are programs! Program: sequence of instructions Machine code: instructions consist of 0’s and 1’s Next slide: example machine code instruction from MIPS (= “Microprocessor without interlocked pipeline stages”) architecture Popular in mid-, late 90s Instructions are 4 bytes longCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland3Example MIPS Instruction “Add data in addresses 1, 2, store result in address 6”:00000000001000100011000000100000 ???000000 00001 00010 00110 00000 100000opcode1staddress2ndaddressdestination addressshift amountfunction specifierCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland4Programming in 1GLsCourtesy of Microsoft Encarta Encyclopedia Online. Copyright (c) Microsoft Encarta OnlineCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland52ndGeneration: Assembly Problem with 1GLs: Who can remember those opcodes, addresses, etc. as 0’s, 1’s? Solution (1950s): assembly language Use mnemonics = descriptive character strings for opcodes Let programmers give descriptive names to addresses MIPS example revisited:add $1, $2, $6instead of00000000001000100011000000100000for “add contents of addresses 1, 2, store result in 6”CMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland6Assemblers Computers still only work on machine code (1GL) Assembly language is not machine code Assemblers are programs that convert assembly language to machine code (= “object code”)asmassemblerobjCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland73rdGeneration: Procedural LanguagesProblems with 2GLs Platform dependency Different kinds (architectures) of computers use different instruction formatsE.g. x86, Pentium, 68K, MIPS, SPARC, etc. 1GL / 2GL programs written for one kind of machine will not work on another Low level: programs difficult to understand Solution (60s -- now): procedural languages Higher-level, “universal” constructs Examples: Fortran, Algol, Pascal, C, C++, Java, C#CMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland8Compilers Computers can only execute machine code Compilers are programs for translating 3GL programs (“source code”) into assembler / machine codesourcecompilerasmCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland9Interpeters Another way to execute 3GL programs Interpreters take source code as input Interpreters execute source directly Much slower than compiled programs Debuggers are based on interpreters Debuggers support step-by-step execution of source code Internal behavior of program can be closely inspectedCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland10This CourseHow to write programs in procedural languages Language is Java Principles are broadly applicableCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland11Tools for Writing Programs The bad old days Text editor: used to create files of source code Compiler: generate executables from source Debugger: trace programs to locate errors Today: IDEs (= “interactive / integrated development environment”) Text editor / compiler / debugger rolled in one Examples: Eclipse, Visual Studio, etc.CMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland12Basics of Eclipse www.cs.umd.edu/eclipse/EclipseTutorial/ Eclipse is used to: Create Edit Compile Run Debugprograms (for this class, Java programs).CMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland13Basics of Eclipse-speak Project: collection of related source filesTo create a program in Eclipse: Create a new project Create files in the project Perspective: framework for manipulating programs Important perspectives in this class: Java: for creating, running programs Debug: for tracing, removing errors in programs CVS repository: for interacting with assignment-submission systemCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland14Eclipse DemoCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland15Class Projects with CVS You will use Eclipse for Java programming in this course How will you: obtain turn inclass projects? CVS (= Concurrent Versions System) Tool for project-file management Maintains versions, etc. Allows different sites to work on same projectCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland16CVS WorldviewFiles =“repository”ServerFiles(local copies)Client 1Files(local copies)Client 2“checkout”“checkout”“commit”“commit”CMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland17CVS in More Detail CVS server maintains current versions of files in project (= “repository”) To access files from another machine (“client”), repository must be “checked out” Changes to files on client may be “committed” to server, with changed files becoming new version (Once a repository is checked out by a client, subsequent versions may be accessed via “update”)CMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland18What’s Needed for CVS? Server machineFor CMSC 131, CS linuxlab machines User authenticationFor CMSC 131, student linuxlab accountsCMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland19How CMSC Project Submission WorksRepository created for each student linuxlabaccount You check out repository to start work on project When you “save” changes in Eclipse, “commit”automatically invoked by plug-ins You “submit” when finished using Eclipse (UMD plug-in handles relevant CVS commands)CMSC 131 Fall 2006Rance Cleaveland©2006 University of Maryland20To Checkout a Project1. Set
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