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Date: Tue, 05 Nov 1996 00:27:24 GMTServer: NCSA/1.5Content-type: text/htmlLast-modified: Thu, 31 Oct 1996 21:38:52 GMTContent-length: 7405<html><head><title>CS 537 - Programming Assignment I</title></head><body bgcolor="#ffffff"><h1>CS 537<br>Programming Assignment I</h1><h2> Due: </h2> September 17 at the <strong>start</strong> of class<hr><h2>Contents</h2><ul><li> <!WA0><a href="#intro"> Introduction</a><li> <!WA1><a href="#suggestions">Suggestions</a><li> <!WA2><a href="#scanning"> Scanning</a><li> <!WA3><a href="#commands"> Commands</a><li> <!WA4><a href="#threads"> Using Threads</a><li> <!WA5><a href="#exceptions"> Exceptions</a><li> <!WA6><a href="#grading"> Grading</a><li> <!WA7><a href="#misc"> Other Stuff</a></ul><hr><a name="intro"> <h2> Introduction </h2> </a><p>The purpose of this assignment is to introduce you to Java programming. You are to implement a simple shell (command interpreter) that behaves similarly to the UNIX shell. When you type in a command (in response to its prompt), it will create a thread that will execute the command you entered. Multiple commands can be chained together on a single line,separated by `&' (ampersand) characters. Your shell will create athread for each individual command and prompt for moreuser input when they have all finished.<p>Unlike the real shell, your program only has to deal with a handful of``built-in'' commands:<table align=center width="80%"><tr> <td> <b>cat</b> <i>file ...</i> <td> Print the contents of the named files to <samp>System.out</samp> one after the other.<tr> <td> <b>cmp</b> <i>file1 file2</i> <td> Check whether the two files have identical contents and print an appropriate message to <samp>System.out</samp>.<tr> <td> <b>sort</b> <i>file</i> <td> Print the lines of <i>file</i> in sorted (lexicographic) order.<tr> <td> <b>exit</b> <td> Terminate the program. You should also terminate on reaching end-of-file on <samp>System.in</samp>.</table>You needn't implement pipes or re-direction of standard input and standard output, but you must be able to handle an arbitrary number of commands per line -- each with an arbitrary number of arguments separated by arbitrary amounts of white space (blanks or tabs) (although only <em>cat</em>takes more than two arguments).<a name="suggestions"> <h2> Suggestions </h2> </a>Your <samp>public static void main()</samp> procedure in your primary classwill be quite simple. It will be an infinite loop that prints a prompt, readsa line (in other courses, a program with an infinite loop is considered a badthing, but in Operating systems, it's the norm!),parses it (breaks it up into its constituent commands),starts a new thread to handle each of the different commands,and then waits for all the threads to finish before printing the next prompt.<a name="scanning"> <h2>Scanning </h2> </a>For scanning, you may find it easier to read the entire line into a Stringobject. The<!WA8><a href="http://www.cs.wisc.edu/~cs537-1/java/api/java.lang.System.html#10726"><B>System.in</B> </a>object is of type<!WA9><a href="http://www.cs.wisc.edu/~cs537-1/java/api/java.io.InputStream.html"><B>InputStream</B>, </a>so it can read either single bytes or arrays of bytes.You could represent an input line as an array of bytes, but you will findit much easier to use a<!WA10><a href="http://www.cs.wisc.edu/~cs537-1/java/api/java.lang.String.html"><B>String</B> </a>instead. You may want to look into the class<!WA11><a href="http://www.cs.wisc.edu/~cs537-1/java/api/java.io.DataInputStream.html"><B>DataInputStream</B> </a>to figure out how to read a line into a String.Tokenizing a String is made almost trivial using the<!WA12><a href="http://www.cs.wisc.edu/~cs537-1/java/api/java.util.StringTokenizer.html"><B>StringTokenizer</B> </a>class found in<!WA13><a href="http://www.cs.wisc.edu/~cs537-1/java/api/javae.htm"><I>java.util</I> </a>.<a name="commands"> <h2>Commands </h2> </a>For the <B>cat</B> command, you should look at the class <!WA14><ahref="http://www.cs.wisc.edu/~cs537-1/java/api/java.io.FileInputStream.html"> <B>FileInputStream</B></a> to see how to read data from a file. <B>cmp</B> will be similar to cat,but this time the contents of the two files will be compared. For <B>sort</B>,an efficient sorting algorithm is not required; anything that works is ok.You might want to adapt the insertion sort used to introduce Java inthe discussion sections.Some of the classes that might help you here are the <!WA15><ahref="http://www.cs.wisc.edu/~cs537-1/java/api/java.io.DataInputStream.html"> <B>DataInputStream</B></a> class and the <!WA16><a href="http://www.cs.wisc.edu/~cs537-1/java/api/java.util.Vector.html"><B>Vector</B> </a> class.<a name="threads"> <h2>Using Threads </h2> </a>Your primary class will read a command from a user and then will create athread to carry out the command. It will then wait until the thread hasfinished before continuing its own execution. There are two ways to startthreads in Java. The first is to derive your class from the <!WA17><ahref="http://www.cs.wisc.edu/~cs537-1/java/api/java.lang.Thread.html"> <B>Thread</B> </a> class andthen override its <samp>run()</samp> function (see pp. 161-162 in <!WA18><ahref="http://www.cs.wisc.edu/~cs537-1/cs537.html#java-book"> the text</a>). The second is to use the <!WA19><ahref="http://www.cs.wisc.edu/~cs537-1/java/api/java.lang.Runnable.html#42925"> <B>Runnable</B> </a>interface (pp. 177-178). Here you create a class that implements thisinterface. You then pass a reference to this class into the constructor of anew thread object. The former is perhaps easier to understandconceptually but the latter is more general. You may chooseeither method for this assignment.<a name="exceptions"> <h2>Exceptions </h2> </a>Java requires you to place within a <B>try</B> block any methods that mightcause an exception. Following the try block is a <B>catch</B> clause(or catch clauses) that willbe used to catch any exceptions that have been thrown (see chapter 7 for moredetails on the syntax of these statements). Your code should deal withexceptions in an appropriate manner. For example, exceptions such asattempting to open a file that does not exist should result in a message to the user and the continuation of the program. More serious exceptions may require an error message followed by program termination (using<!WA20><a href="http://www.cs.wisc.edu/~cs537-1/java/api/java.lang.System.html#10832"><samp>System.exit()</samp></a>).<a name="grading"> <h2>Grading </h2> </a>Hand in your source program and a transcript of a terminal session which demonstrates your shell's ability to perform as specified (see <samp>script(1)</samp>). Be sure that you use test data adequate to exercise your program's capabilities. You should follow all the principles of software engineering you learned in CS 302 and CS 367, including top-down design, good indentation, meaningful variable names, modularity, and helpful comments. You will be graded not only on the basis of correctness, but also programmingstyle and completeness of test data.<a name="misc"> <h2> Other Stuff </h2> </a>For those of you writing your programs on the Solaris machines, you might consider usinga makefile to aid in compilation. Those of you using DOS may want to look into <B>doskey</B>, a little program that provides for easy command manipulation. Feel free to send any otherwork-saving methods you find to<!WA21><A HREF="mailto:mellen@cs.wisc.edu">the ta</a>, and he will distribute them to the class.<hr><address><i><!WA22><a HREF="mailto:solomon@cs.wisc.edu">solomon@cs.wisc.edu</a><br>Thu Oct 31 15:38:52 CST 1996</i></address><br>Copyright © 1996 by Marvin Solomon. All rights reserved.</body></html>⌨️ 快捷键说明
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