csHjavaA-2019

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read text files

key points about file handling, introductory projects, (includes substring)

internet domain names

Scottish Council voters

examScores

Here are the main steps for file handling and also some sample Java code to see who it works.

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What do text files look like? 💾

One or more lines of text, each separated by a newline (\n) :

Aberdeen City\nAberdeenshire\nAngus\nArgyll & Bute\nCity of Edinburgh(EndOfFile)

normally displays like this:

Aberdeen City

Aberdeenshire

Angus

Argyll & Bute

City of Edinburgh

text files can store digits but they are still represented as text characters rather than coded as integers

145832\n192269\n86548\n65512\n343748(EndOfFile)

normally displays like this:

145832

192269

86548

65512

343748

reading a file: main steps

open file

read from file

this will often involve a loop to repeat the read step for every line in a file

close file

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reading from file: java

Reading text files is quite similar to reading a series of keyboard entries.

An attempt to read beyond the end of the file will normally cause an error and could cause the program to crash.

open a text file

// identify file

String inputFile = "filename.txt";

// java file reader, opens file named by inputFile

Scanner fileReader = new Scanner(new File(inputFile));

store the name of the file

use the name of the file to create a Scanner for the file, call it fileReader

read next value from file as a String, store in an array (nest within a loop)

textList[i] = fileReader.nextLine();

read one line form the file and store it as text into the next position in the array

this code uses a loop index [i] to identify a position in a String array called textList

close the file

fileReader.close();

additional file handling code for Java

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Java needs additional code to make file reading (and writing) work properly and to deal with any file errors

additional code needed for working with file in Java

import java.util.*;

import java.io.*;

Java needs to include additional features to make file handling work, add to the top of the program

dealing with file handling errors

throws IOException

Java needs to know how to report any file errors, add this code at the start of methods that depend on file handling

What do text files look like? 💾

reading a file: main steps

reading from file: java

additional file handling code for Java

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