DOCSLIB.ORG

Console Streams

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Console Streams I/O Package Overview Computer Science and Engineering The Ohio State University Package java.io IO Core concept: streams Computer Science and Engineering College of Engineering The Ohio State University Ordered sequences of data that have a source (for input) or a destination (for output) Two major flavors: Lecture 21 Byte streams 8 bits, data-based Input streams and output streams Character streams 16 bits, text-based Readers and writers See Java API documentation for details Byte Streams Example 1: Counting Characters Computer Science and Engineering The Ohio State University Computer Science and Engineering The Ohio State University Two abstract base classes: InputStream and OutputStream import java.io.*; InputStream (for reading bytes) defines: class CountBytes { An abstract method for reading 1 byte at a time public abstract int read() public static void main(String[] args) Returns next byte value (0-255) or -1 if end-of-stream throws IOException { encountered Concrete input stream overrides this method to provide useful InputStream in = new FileInputStream(args[0]); functionality int total = 0; Methods to read an array of bytes or skip a number of bytes OutputStream (for writing bytes) defines: while (in.read() != -1) { An abstract method for writing 1 byte at a time total++; public abstract void write(int b) } Upper 24 bits are ignored Methods to write bytes from a specified byte array in.close(); Close the stream after reading/writing System.out.println(total + ” bytes”); public void close() Frees up limited operating system resources } All of these methods can throw IOException } Standard Streams Example 2: Console Streams Computer Science and Engineering The Ohio State University Computer Science and Engineering The Ohio State University Three standard streams for console IO import java.io.*; class TranslateBytes { System.in public static void main(String[] args) Input from keyboard throws IOException { System.out byte from = (byte)args[0].charAt(0); Output to console byte to = (byte)args[1].charAt(0); System.err int x; Output to error (console by default) while((x = System.in.read()) != -1) These streams are byte streams! System.out.write(x == from ? to : x); } System.in is an InputStream, the others are } PrintStreams (inherit from OutputStream) Would be more logical for these to be character If you run “java TranslateBytes b B” and enter text streams not byte streams, but they predate the bigboy via the keyboard the output will be: BigBoy inclusion of character streams in Java 1 Character Streams Converting Byte/Character Streams Computer Science and Engineering The Ohio State University Computer Science and Engineering The Ohio State University Two abstract base classes: Reader and Writer Translation supported by conversion streams: InputStreamReader and OutputStreamWriter Similar methods to byte stream counterparts Subclasses of Reader and Writer respectively Reader abstract class defines: InputStreamReader public int read() public InputStreamReader(InputStream in) Returns value in range 0..65535 (or -1) public InputStreamReader(InputStream in, String encoding) An encoding is a standard map of characters to bits (eg UTF-16) public int read(char[] cbuf) public int read() Returns number of characters read Reads bytes from associated InputStream and converts them to public void skip(int n) characters using the appropriate encoding for that stream OutputStreamWriter Writer abstract class defines: public OutputStreamWriter(OutputStream out) public void write(int c) public OutputStreamWriter(OutputStream out, String enc) public void write(char[] cbuf) public void write(int c) public abstract void flush() Converts argument to bytes using the appropriate encoding and writes these bytes to its associated OutputStream Ensures previous writes have been sent to destination Closing the conversion stream also closes the associated byte Useful for buffered streams stream – may not always desirable Both classes define: public void close() Working with Files Efficient IO Computer Science and Engineering The Ohio State University Computer Science and Engineering The Ohio State University A file can be identified in one of three ways Buffering greatly improves IO performance A String object (file name) Example: BufferedReader for character input A File object streams A FileDescriptor object public BufferedReader(Reader in) Sequential-Access file: read/write at end of stream only The buffered stream “wraps” the unbuffered FileInputStream, FileOutputStream, FileReader, stream FileWriter Example declarations of BufferedReaders Each file stream type has three constructors An InputStreamReader inside a BufferedReader Random-Access file: read/write at a specified location Reader r = new InputStreamReader(System.in); RandomAccessFile BufferedReader in = new BufferedReader(r); A file pointer is used to guide the starting position A FileReader inside a BufferedReader Not a subclass of any of the four basic IO classes Reader fr = new FileReader(“fileName”); (InputStream, OutputStream, Reader, or Writer) BufferedReader in = new BufferedReader(fr); Supports both input and output Then you can invoke in.readLine() to read from Supports both bytes and characters the stream line by line Example: A Random Access File The File Class Computer Science and Engineering The Ohio State University Computer Science and Engineering The Ohio State University class Filecopy { Useful for retrieving information about a file or a public static void main(String args[]) { RandomAccessFile fh1 = null; directory RandomAccessFile fh2 = null; Represents a path, not necessarily an underlying file try { Does not open/close files or provide file-processing fh1 = new RandomAccessFile(args[0], “r”); capabilities fh2 = new RandomAccessFile(args[1], “rw”); } catch (FileNotFoundException e) { Three constructors System.out.println(“File not found”); public File(String name) System.exit(100); public File(String pathToName, String name) } public File(File directory, String name) try { Main methods int bufsize = (int) (fh1.length())/2; byte[] buffer1 = new byte[bufsize]; boolean canRead() / boolean canWrite() fh1.readFully(buffer1, 0, bufsize); boolean exists() fh2.write(buffer1, 0, bufsize); } catch (IOException e) { boolean isFile() / boolean isDirectory() System.out.println("IO error occurred!"); String getAbsolutePath() / String getPath() System.exit(200); String getParent() } } String getName() } long length() long lastModified() 2 Example Computer Science and Engineering The Ohio State University public class EfficientReader { public static void main (String[] args) { try { Reader fr = new FileReader(args[0]); BufferedReader br = new BufferedReader(fr) String line = br.readLine(); while (line != null) { System.out.println("Read a line:"); System.out.println(line); line = br.readLine(); } br.close(); } catch(FileNotFoundException e) { System.out.println(“File not found: ” + args[0]); } catch(IOException e) { System.out.println(“Can’t read from file: ” + args[0]); } } } 3.
Load more

Recommended publications
  • CS 61A Streams Summer 2019 1 Streams
    CS 61A Streams Summer 2019 Discussion 10: August 6, 2019 1 Streams In Python, we can use iterators to represent infinite sequences (for example, the generator for all natural numbers). However, Scheme does not support iterators. Let's see what happens when we try to use a Scheme list to represent an infinite sequence of natural numbers: scm> (define (naturals n) (cons n (naturals (+ n 1)))) naturals scm> (naturals 0) Error: maximum recursion depth exceeded Because cons is a regular procedure and both its operands must be evaluted before the pair is constructed, we cannot create an infinite sequence of integers using a Scheme list. Instead, our Scheme interpreter supports streams, which are lazy Scheme lists. The first element is represented explicitly, but the rest of the stream's elements are computed only when needed. Computing a value only when it's needed is also known as lazy evaluation. scm> (define (naturals n) (cons-stream n (naturals (+ n 1)))) naturals scm> (define nat (naturals 0)) nat scm> (car nat) 0 scm> (cdr nat) #[promise (not forced)] scm> (car (cdr-stream nat)) 1 scm> (car (cdr-stream (cdr-stream nat))) 2 We use the special form cons-stream to create a stream: (cons-stream <operand1> <operand2>) cons-stream is a special form because the second operand is not evaluated when evaluating the expression. To evaluate this expression, Scheme does the following: 1. Evaluate the first operand. 2. Construct a promise containing the second operand. 3. Return a pair containing the value of the first operand and the promise. 2 Streams To actually get the rest of the stream, we must call cdr-stream on it to force the promise to be evaluated.
    [Show full text]
  • Chapter 2 Basics of Scanning And
    Chapter 2 Basics of Scanning and Conventional Programming in Java In this chapter, we will introduce you to an initial set of Java features, the equivalent of which you should have seen in your CS-1 class; the separation of problem, representation, algorithm and program – four concepts you have probably seen in your CS-1 class; style rules with which you are probably familiar, and scanning - a general class of problems we see in both computer science and other fields. Each chapter is associated with an animating recorded PowerPoint presentation and a YouTube video created from the presentation. It is meant to be a transcript of the associated presentation that contains little graphics and thus can be read even on a small device. You should refer to the associated material if you feel the need for a different instruction medium. Also associated with each chapter is hyperlinked code examples presented here. References to previously presented code modules are links that can be traversed to remind you of the details. The resources for this chapter are: PowerPoint Presentation YouTube Video Code Examples Algorithms and Representation Four concepts we explicitly or implicitly encounter while programming are problems, representations, algorithms and programs. Programs, of course, are instructions executed by the computer. Problems are what we try to solve when we write programs. Usually we do not go directly from problems to programs. Two intermediate steps are creating algorithms and identifying representations. Algorithms are sequences of steps to solve problems. So are programs. Thus, all programs are algorithms but the reverse is not true.
    [Show full text]
  • File I/O Stream Byte Stream
    File I/O In Java, we can read data from files and also write data in files. We do this using streams. Java has many input and output streams that are used to read and write data. Same as a continuous flow of water is called water stream, in the same way input and output flow of data is called stream. Stream Java provides many input and output stream classes which are used to read and write. Streams are of two types. Byte Stream Character Stream Let's look at the two streams one by one. Byte Stream It is used in the input and output of byte. We do this with the help of different Byte stream classes. Two most commonly used Byte stream classes are FileInputStream and FileOutputStream. Some of the Byte stream classes are listed below. Byte Stream Description BufferedInputStream handles buffered input stream BufferedOutputStrea handles buffered output stream m FileInputStream used to read from a file FileOutputStream used to write to a file InputStream Abstract class that describe input stream OutputStream Abstract class that describe output stream Byte Stream Classes are in divided in two groups - InputStream Classes - These classes are subclasses of an abstract class, InputStream and they are used to read bytes from a source(file, memory or console). OutputStream Classes - These classes are subclasses of an abstract class, OutputStream and they are used to write bytes to a destination(file, memory or console). InputStream InputStream class is a base class of all the classes that are used to read bytes from a file, memory or console.
    [Show full text]
  • Chapter 10 Streams Streams Text Files and Binary Files
    Streams Chapter 10 • A stream is an object that enables the flow of File I/O data between a ppgrogram and some I/O device or file – If the data flows into a program, then the stream is called an input stream – If the dtdata flows out of a program, then the stream is called an output stream Copyright © 2012 Pearson Addison‐Wesley. All rights reserved. 10‐2 Streams Text Files and Binary Files • Input streams can flow from the kbkeyboar d or from a • Files that are designed to be read by human beings, file and that can be read or written with an editor are – StSystem. in is an itinput stream tha t connects to the called text files keyboard – Scanner keyy(y);board = new Scanner(System.in); Text files can also be called ASCII files because the data they contain uses an ASCII encoding scheme • Output streams can flow to a screen or to a file – An advantage of text files is that the are usually the same – System.out is an output stream that connects to the screen on all computers, so tha t they can move from one System.out.println("Output stream"); computer to another Copyright © 2012 Pearson Addison‐Wesley. All rights reserved. 10‐3 Copyright © 2012 Pearson Addison‐Wesley. All rights reserved. 10‐4 Text Files and Binary Files Writing to a Text File • Files tha t are didesigne d to be read by programs and • The class PrintWriter is a stream class that consist of a sequence of binary digits are called binary files that can be used to write to a text file – Binary files are designed to be read on the same type of – An object of the class PrintWriter has the computer and with the same programming language as the computer that created the file methods print and println – An advantage of binary files is that they are more efficient – These are similar to the System.out methods to process than text files of the same names, but are used for text file – Unlike most binary files, Java binary files have the advantage of being platform independent also output, not screen output Copyright © 2012 Pearson Addison‐Wesley.
    [Show full text]
  • C++ Input/Output: Streams 4
    C++ Input/Output: Streams 4. Input/Output 1 The basic data type for I/O in C++ is the stream. C++ incorporates a complex hierarchy of stream types. The most basic stream types are the standard input/output streams: istream cin built-in input stream variable; by default hooked to keyboard ostream cout built-in output stream variable; by default hooked to console header file: <iostream> C++ also supports all the input/output mechanisms that the C language included. However, C++ streams provide all the input/output capabilities of C, with substantial improvements. We will exclusively use streams for input and output of data. Computer Science Dept Va Tech August, 2001 Intro Programming in C++ ©1995-2001 Barnette ND & McQuain WD C++ Streams are Objects 4. Input/Output 2 The input and output streams, cin and cout are actually C++ objects. Briefly: class: a C++ construct that allows a collection of variables, constants, and functions to be grouped together logically under a single name object: a variable of a type that is a class (also often called an instance of the class) For example, istream is actually a type name for a class. cin is the name of a variable of type istream. So, we would say that cin is an instance or an object of the class istream. An instance of a class will usually have a number of associated functions (called member functions) that you can use to perform operations on that object or to obtain information about it. The following slides will present a few of the basic stream member functions, and show how to go about using member functions.
    [Show full text]
  • HP C Run-Time Library Reference Manual for Openvms Systems
    HP C Run-Time Library Reference Manual for OpenVMS Systems Order Number: BA554-90014 June 2010 This manual describes the functions and macros in the HP C Run-Time Library for OpenVMS systems. Revision/Update Information: This manual supersedes the HP C Run-Time Library Reference Manual for OpenVMS Systems, Version 8.3 Software Version: OpenVMS Version 8.4 for Integrity servers OpenVMS Alpha Version 8.4 Hewlett-Packard Company Palo Alto, California © Copyright 2010 Hewlett-Packard Development Company, L.P. Confidential computer software. Valid license from HP required for possession, use or copying. Consistent with FAR 12.211 and 12.212, Commercial Computer Software, Computer Software Documentation, and Technical Data for Commercial Items are licensed to the U.S. Government under vendor’s standard commercial license. The information contained herein is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services. Nothing herein should be construed as constituting an additional warranty. HP shall not be liable for technical or editorial errors or omissions contained herein. UNIX is a registered trademark of The Open Group. X/Open is a registered trademark of X/Open Company Ltd. in the UK and other countries. Intel and Itanium are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States and other countries. Microsoft and Windows are US registered trademarks of Microsoft Corporation. Printed in the US ZK5763 The HP OpenVMS documentation set is available on CD-ROM. This document was prepared using DECdocument, Version 3.3-1b.
    [Show full text]
  • Subtyping, Declaratively an Exercise in Mixed Induction and Coinduction
    Subtyping, Declaratively An Exercise in Mixed Induction and Coinduction Nils Anders Danielsson and Thorsten Altenkirch University of Nottingham Abstract. It is natural to present subtyping for recursive types coin- ductively. However, Gapeyev, Levin and Pierce have noted that there is a problem with coinductive definitions of non-trivial transitive inference systems: they cannot be \declarative"|as opposed to \algorithmic" or syntax-directed|because coinductive inference systems with an explicit rule of transitivity are trivial. We propose a solution to this problem. By using mixed induction and coinduction we define an inference system for subtyping which combines the advantages of coinduction with the convenience of an explicit rule of transitivity. The definition uses coinduction for the structural rules, and induction for the rule of transitivity. We also discuss under what condi- tions this technique can be used when defining other inference systems. The developments presented in the paper have been mechanised using Agda, a dependently typed programming language and proof assistant. 1 Introduction Coinduction and corecursion are useful techniques for defining and reasoning about things which are potentially infinite, including streams and other (poten- tially) infinite data types (Coquand 1994; Gim´enez1996; Turner 2004), process congruences (Milner 1990), congruences for functional programs (Gordon 1999), closures (Milner and Tofte 1991), semantics for divergence of programs (Cousot and Cousot 1992; Hughes and Moran 1995; Leroy and Grall 2009; Nakata and Uustalu 2009), and subtyping relations for recursive types (Brandt and Henglein 1998; Gapeyev et al. 2002). However, the use of coinduction can lead to values which are \too infinite”. For instance, a non-trivial binary relation defined as a coinductive inference sys- tem cannot include the rule of transitivity, because a coinductive reading of transitivity would imply that every element is related to every other (to see this, build an infinite derivation consisting solely of uses of transitivity).
    [Show full text]
  • L13 Streams and IO
    Binghamton CS-220 University Spring 20162015 Includes & Streams 1 Binghamton CS-220 University Spring 20162015 C Pre-Processor C Program Pre-Processor Pre-processed C Program Header Files Header Files 2 Binghamton CS-220 University Spring 20162015 #include • Two flavors: • #include <abc.h> • Replace this line with the contents of file abc.h found in the system libraries • #include “xyz.h” • Replace this line with the contents of file xyz.h found in the current directory • Concept: Write code once, use it in many different programs • By convention, included files are called “header files” and have a “.h” file type 3 Binghamton CS-220 University Spring 20162015 Header (.h) files • May include any valid C code • may include further #includes • Typically small – only what you need to invoke “outside” functions • Function prototype declarations • Sometimes, data and/or type declarations • Typically, a header file describes a group of functions • “related” functions – e.g. functions which deal with Input and Output • Typically associated with a “.c” file with the same name • .c file contains function definitions – more later 4 Binghamton CS-220 University Spring 20162015 C Standard Library • Part of C itself • Definitions/Descriptions included in C standard • Available with every C compiler • Primarily, a set of C functions we all can use • Keep C language simple • Wrap complicated stuff in function definitions • We don’t need to know about the implementation of the complicated stuff • Full description of standard library available as reference • Programming in C, Appendix B 5 Binghamton CS-220 University Spring 20162015 Standard Input and Output • Need: #include <stdio.h> • Large list of input and output functions to: • Read and write from a “stream” • Open a file and make a stream • Close a file and remove the stream • Create, Rename, delete, or move files • Streams….
    [Show full text]
  • CS2043 - Unix Tools & Scripting Cornell University, Spring 20141
    CS2043 - Unix Tools & Scripting Cornell University, Spring 20141 Instructor: Bruno Abrahao January 31, 2014 1 Slides evolved from previous versions by Hussam Abu-Libdeh and David Slater Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting Vim: Tip of the day! Line numbers Displays line number in Vim: :set nu Hides line number in Vim: :set nonu Goes to line number: :line number Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting Counting wc How many lines of code are in my new awesome program? How many words are in this document? Good for bragging rights Word, Character, Line, and Byte count with wc wc -l : count the number of lines wc -w : count the number of words wc -m : count the number of characters wc -c : count the number of bytes Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting Sorting sort Sorts the lines of a text file alphabetically. sort -ru file sorts the file in reverse order and deletes duplicate lines. sort -n -k 2 -t : file sorts the file numerically by using the second column, separated by a colon Example Consider a file (numbers.txt) with the numbers 1, 5, 8, 11, 62 each on a separate line, then: $ sort numbers.txt $ sort numbers.txt -n 1 1 11 5 5 8 62 11 8 62 Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting uniq uniq uniq file - Discards all but one of successive identical lines uniq -c file - Prints the number of successive identical lines next to each line Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting Character manipulation! The Translate Command tr [options] <char_list1> [char_list2] Translate or delete characters char lists are strings of characters By default, searches for characters in char list1 and replaces them with the ones that occupy the same position in char list2 Example: tr 'AEIOU' 'aeiou' - changes all capital vowels to lower case vowels Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting Pipes and redirection tr only receives input from standard input (stdin) i.e.
    [Show full text]
  • Data-Trace Types for Distributed Stream Processing Systems
    Data-Trace Types for Distributed Stream Processing Systems Konstantinos Mamouras Caleb Stanford Rajeev Alur Rice University, USA University of Pennsylvania, USA University of Pennsylvania, USA [email protected] [email protected] [email protected] Zachary G. Ives Val Tannen University of Pennsylvania, USA University of Pennsylvania, USA [email protected] [email protected] Abstract guaranteeing correct deployment, and (2) the throughput of Distributed architectures for efficient processing of stream- the automatically compiled distributed code is comparable ing data are increasingly critical to modern information pro- to that of hand-crafted distributed implementations. cessing systems. The goal of this paper is to develop type- CCS Concepts • Information systems → Data streams; based programming abstractions that facilitate correct and Stream management; • Theory of computation → Stream- efficient deployment of a logical specification of the desired ing models; • Software and its engineering → General computation on such architectures. In the proposed model, programming languages. each communication link has an associated type specifying tagged data items along with a dependency relation over tags Keywords distributed data stream processing, types that captures the logical partial ordering constraints over data items. The semantics of a (distributed) stream process- ACM Reference Format: ing system is then a function from input data traces to output Konstantinos Mamouras, Caleb Stanford, Rajeev Alur, Zachary data traces, where a data trace is an equivalence class of se- G. Ives, and Val Tannen. 2019. Data-Trace Types for Distributed quences of data items induced by the dependency relation. Stream Processing Systems. In Proceedings of the 40th ACM SIGPLAN Conference on Programming Language Design and Implementation This data-trace transduction model generalizes both acyclic (PLDI ’19), June 22–26, 2019, Phoenix, AZ, USA.
    [Show full text]
  • Stream Computing Based Synchrophasor Application for Power Grids
    Stream Computing Based Synchrophasor Application For Power Grids Jagabondhu Hazra Kaushik Das Deva P. Seetharam IBM Research, India IBM Research, India IBM Research, India [email protected] [email protected] [email protected] Amith Singhee IBM T J Watson Research Center, USA [email protected] ABSTRACT grid monitoring to identify and deal with faults before they develop This paper proposes an application of stream computing analytics into wide-spread disturbances. framework to high speed synchrophasor data for real time moni- In recent years, electric grids are undergoing dramatic changes toring and control of electric grid. High volume streaming syn- in the area of grid monitoring and control. Key factors behind chrophasor data from geographically distributed grid sensors (namely, such transformation includes tremendous progress in the areas of Phasor Measurement Units) are collected, synchronized, aggregated power electronics, sensing, control, computation and communi- when required and analyzed using a stream computing platform to cation technologies. For instant, conventional sensors (e.g. Re- estimate the grid stability in real time. This real time stability mon- mote Terminal Units) provide one measurement or sample per 4- itoring scheme will help the grid operators to take preventive or 10 seconds whereas new sensors like Phasor Measurement Units corrective measures ahead of time to mitigate any disturbance be- (PMUs) could provide upto 120 measurements or samples per sec- fore they develop into wide-spread. A protptype of the scheme is ond. Moreover, PMUs provide more precise measurements with demonstrated on a benchmark 3 machines 9 bus system and the time stamp having microsecond accuracy [2].
    [Show full text]
  • Preprocessing C++ : Meta-Class Aspects
    Preprocessing C++ : Meta-Class Aspects Edward D. Willink Racal Research Limited, Worton Drive, Reading, England +44 118 923 8278 [email protected] Vyacheslav B. Muchnick Department of Computing, University of Surrey, Guildford, England +44 1483 300800 x2206 [email protected] ABSTRACT C++ satisfies the previously conflicting goals of Object-Orientation and run-time efficiency within an industrial strength language. Run-time efficiency is achieved by ignoring the meta-level aspects of Object-Orientation. In a companion paper [15] we show how extensions that replace the traditional preprocessor lexical substitution by an Object-Oriented meta-level substitution fit naturally into C++. In this paper, we place those extensions in the context of a compile-time meta-level, in which application meta-programs can execute to browse, check or create program declarations. An extended example identifies the marshalling aspect as a programming concern that can be fully separated and automatically generated by an application meta-program. Keywords Object-Oriented Language; Preprocessor; C++; Meta-Level; Composition; Weaving; Aspect-Oriented Programming; Pattern Implementation 1 INTRODUCTION Prior to C++, Object Orientation, as exemplified by Smalltalk, was perceived to be inherently inefficient because of the run-time costs associated with message dispatch. C++ introduced a more restrictive Object Model that enabled most of the run-time costs to be resolved by compile-time computation. As a result Object Orientation in C++ is efficient and widely used. C++ requires that the layout of objects be frozen at compile-time, and that the type of the recipient of any message is known. The layout constraint enables a single contiguous memory allocation for each object.
    [Show full text]