How do you read and write to text files?

[stevepuri]

Hey,

Does anyone know how to read
and write to text files in Java?



In C++, to read a file, you would do:
(stores the contents into array "data&quot

ifstream f("myFile.txt")
char ch;
char* data = " ";
while (f.get(ch))
{
    data << ch;
}
f.close();

In C++, to write to a file, you would do:
(writes "Hello, world!" to myFile.txt)

ofstream g("myFile.txt");
g << &quot;Hello, world!&quot; << &quot;\n&quot;;
g.close();

Anyone have the Java equivalent?

Thanks,
Steve.

 

[GIGN]

Well, I have only just begun doing this - so it is probably inelegant but I do somrthing like:

Reading
1. Create FileReader
2. Read from file to charArray (buffer) using FileReader
3. Call function to read char array and print to wherever.
This is the function I used to read, I don't think it is
the most eficient, but I was in hurry

private String readFromABuffer(char[] charBuffer){
String output = new String();
// fill the string with characters
for(int j=0;j<charBuffer.length;j++){
Character newChar = new Character(charBuffer[j]);
String fromBuffer = newChar.toString();
output = output.concat(fromBuffer);
}
return output;
}
This returns a string which can be written to a textArea. I had to use this function because the filereader's read method returns a character array.

Saving is more straight forward:
/** This function is responsible for:
1. Getting an output stream -
2. Writing the data.
3. Saving.
*/
private void save(){

// get text to save
String data = this.txt.getText();

try{
canWrite = theFile.canWrite();
out = new FileWriter(theFile);
System.out.println(&quot;FileWriter created&quot;
}
catch(SecurityException s){
System.err.println(&quot;Cannot write to this file&quot;
}
catch(NullPointerException n){
System.err.println(&quot;File not there.&quot;
}
catch(IOException io){
System.err.println(&quot;IO error - no file or something...&quot;
}
// write data to file
try{
if(canWrite){
out.write(data);
}
else{
System.out.println(&quot;Cannot overwrite file..&quot;
}
out.close()
System.out.println(&quot;String.written&quot;

}
catch(IOException io){
System.err.println(&quot;Error writing to file.&quot;
}
}


There are some global variables here, sorry:
boolean canWrite;
FileReader in;
FileWriter out;
File theFile;
TextArea txt;

check out you javadocs for more details of these methods.

b[sup]2[/sup] - benbiddington@surf4nix.com

 

[Miros]

There's a good example in Java for Students.

However, applets can't read and write to the local drive; only applications. You can read from a file on the internet the same way, but you have to use ftp to upload them again.

Rose

 

[pipk]

Hi

Just in case you wanted to know, Per Brinch Hansen has some read/write classes he has written for tutorial purposes, but they are actually pretty useful if you are just reading a byte stream.

You can download them at ftp.cis.syr.edu from within pbh/textprogram directory. The file is called Text.java.

pipk