java io stream

binary file input

• FileInputStream
• BufferedInputStream

InputStream in = new BufferedInputStream (new FileInputStream (fileName));
byte[] data = new byte[1024];
int length = in.read(data);

read() returns length of binary number it gets and save the number to data. when it reads nothing, read() returns -1.

binary file output

• FileOutputStream
• BufferedInputStream

OutputStream out = new BufferedOutputStream (new FileOutputStream (fileName));
out.writer (data, 0, length);

writer() gets numbers of data from 0 to length, and saves them to file.

binary file io example

InputStream in = new BufferedInputStream (new FileInputStream (inFileName));
OutputStream out = new BufferedOutputStream (new FileOutputStream (outFileName));
byte[] data = new byte[1024];
int length = -1;

while ((length = in.read (data)) != -1) {
  out.writer (data, 0, length);
}

in.close();
out.close();

it should be noticed that in and out must be close(), or the file will not be changed.

text file input

• File
• FileReader
• BufferedReader

File infile = new File (inFileName);
BufferedReader in = new BufferedReader (new FileReader(infile));
String s = in.readLine();
in.close();

if readLine() reads nothing, return null;

text file output

• File
• FileWriter
• BufferedWriter

File outfile = new File (outFileName);
BufferedWriter out = new BufferedWriter(new FileWriter(outfile));

out.println(s);

out.close();

text file io example

File infile = new File (inFileName);
File outfile = new File (outFileName);
BufferedReader in = new BufferedReader (FileReader (infile));
BufferedWriter out = new BufferedWriter (FileWriter (outFile));
String string = in.readLine();

while (string != null) {
  out.println(string);
  string = in.readLine();
}

in.close();
out.close();