Files CSI 3125 Preliminaries page 1 Reading and

Files CSI 3125, Preliminaries, page 1

Reading and Writing Files • Java provides a number of classes and methods that allow you to read and write files. • In Java, all files are byte-oriented, and Java provides methods to read and write bytes from and to a file. • Java allows you to wrap a byte-oriented file stream within a character-based object. • The two important streams are File. Input. Stream and File. Output. Stream CSI 3125, Preliminaries, page 2

Reading and Writing Files • To open a file, create an object of one of these classes, specifying the name of the file as an argument to the constructor. • While both classes support additional, overridden constructors • File. Input. Stream(String file. Name) throws File. Not. Found. Exception • File. Output. Stream(String file. Name) throws File. Not. Found. Exception • file. Name specifies the name of the file that you want to open CSI 3125, Preliminaries, page 3

Reading and Writing Files • When create an input stream, if the file does not exist, then File. Not. Found. Exception is thrown. • For output streams, if the file cannot be created, then File. Not. Found. Exception is thrown. CSI 3125, Preliminaries, page 4

Reading and Writing Files • Closing the file • close( ). It is defined by both File. Input. Stream and File. Output. Stream, • void close( ) throws IOException CSI 3125, Preliminaries, page 5

Reading and Writing Files • To read from a file, you can use a version of read( ) that is defined within File. Input. Stream. • int read( ) throws IOException • Each time it reads a single byte from the file and returns the byte as an integer value. • read( ) returns – 1 when the end of the file is encountered. • It can throw an IOException. CSI 3125, Preliminaries, page 6

Reading and Writing Files Prog to read the file popo. java and print each characters in screen • • • • • import java. io. *; class f 1 { public static void main(String a[]) { try{ File. Input. Stream fil=new File. Input. Stream("z. java"); // create object of File. Input. Stream int i; do { i = fil. read(); // read one character at a time System. out. println((char)i); // print in screen }while(i != -1); fil. close(); } catch(Exception e) {System. out. println("Error"); } }} CSI 3125, Preliminaries, page 7

Reading and Writing Files • To write to a file, you will use the write( ) method defined by File. Output. Stream • void write(int byteval) throws IOException • This method writes the byte specified by byteval to the file CSI 3125, Preliminaries, page 8

Reading and Writing Files Prog to copy the file popo. java to copy. java • • • • • • import java. io. *; class f 1 { public static void main(String a[]) { try{ File. Input. Stream fin=new File. Input. Stream("z. java"); // object for file Input File. Output. Stream fout=new File. Output. Stream(“copy. java"); // object for file output int i; do { i = fin. read(); fout. write(i); // write to the copy. java file }while(i != -1); fin. close(); fout. close(); } catch(Exception e) {System. out. println("Error"); } } } CSI 3125, Preliminaries, page 9

Reading and Writing Files CSI 3125, Preliminaries, page 10

Reading and Writing Files Prog to read the file popo. txt and print one line each in the screen • • • • • import java. io. *; class f { public static void main(String a[]) { try{ File. Reader fil=new File. Reader("popo. txt"); // File. Reader reads text files Buffered. Reader br=new Buffered. Reader(fil); // Always wrap File. Reader in Buffered. Reader. String s; while((s=br. read. Line())!=null) //reference one line at a time { System. out. println(s); } br. close(); } catch(Exception e) {System. out. println("Error"); } }} CSI 3125, Preliminaries, page 11

Reading and Writing Files CSI 3125, Preliminaries, page 12