Java Input and Output

Console Class

- used for reading the data from the console and writing the data on the console.

- obtain a reference to the console using the System.console() method.

// get the System console object

Console console = System.console();

// read a line and print it through printf

console.printf(console.readLine());

String userName = null;

char[] password = null;

userName = console.readLine("Enter your username: ");

// typed characters for password will not be displayed in the screen

password = console.readPassword("Enter password: ");

// password is a char[]: convert it to a String first before

Reader classes

- read the contents in the stream and try interpreting them as characters, such as a tab, end-of-file, newline,

// try opening the file with FileReader

try (FileReader inputFile = new FileReader(file)) {

int ch = 0;

// while there are characters to fetch, read, and print the

// characters when EOF is reached, read() will return −1,

// terminating the loop

while( (ch = inputFile.read()) != −1) {

// ch is of type int - convert it back to char

// before printing

System.out.print( (char)ch );

}

} catch (FileNotFoundException fnfe) {

// the passed file is not found ...

System.err.printf("Cannot open the given file %s ", file);

}

catch(IOException ioe) {

// some IO error occurred when reading the file ...

System.err.printf("Error when processing file %s... skipping it", file);

}

// try-with-resources will automatically release FileReader object

BufferedReader and BufferedWriter

// try opening the source and destination file

// with FileReader and FileWriter

try (BufferedReader inputFile = new BufferedReader(new FileReader(srcFile));

BufferedWriter outputFile = new BufferedWriter(new FileWriter(dstFile))) {

int ch = 0;

// while there are characters to fetch, read the characters from

// source stream and write them to the destination stream

while( (ch = inputFile.read()) != −1) {

// ch is of type int - convert it back to char before

// writing it

outputFile.write( (char)ch );

}

// no need to call flush explicitly for outputFile - the close()

// method will first call flush before closing the outputFile stream

} catch (FileNotFoundException fnfe) {

// the passed file is not found ...

System.err.println("Cannot open the file " + fnfe.getMessage());

}

catch(IOException ioe) {

// some IO error occurred when reading the file ...

System.err.printf("Error when processing file; exiting ... ");

}

// try-with-resources will automatically release FileReader object