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CompressedFile.java
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CompressedFile.java
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import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
/**
* Class to open a file and either read information from it or write information
* to it. If a file is opened in "read" mode we can only read information from
* it. Otherwise, we can only write information to it.
*
*/
public class CompressedFile {
// Method readChar() returns this value when the end of the file has been
// reached
public static final char EOF = 0;
private FileInputStream in; // This variable points to the input file
// private BufferedWriter out; // This variable points to the output file
private DataOutputStream out;
private String accessMode; // Determines whether we wish to read from or to
// write to the file
private int bitsRead;
private int bitsWritten;
private char buffer;
/**
* Checks that the specifed name corresponds to an existing file and if so
* it opens the file
*
* @param name
* name of the input file
*/
public CompressedFile(String fileName, String fileMode) {
if (fileMode.equals("read")) {
File file;
file = new File(fileName);
accessMode = "read";
if (!file.exists()) {
System.out.println("File " + fileName + " does not exist.");
System.exit(0); // end program
}
if (!(file.isFile() && file.canRead())) {
System.out.println("file " + fileName + " cannot be read from.");
System.exit(0);
}
try {
in = new FileInputStream(file); // Get ready to read from the
// file
bitsRead = 8; // Forces a new character to be read when method
// readChar is invoked
} catch (IOException e) {
System.out.println("Error opening file " + fileName);
System.exit(0);
}
} else {
FileOutputStream fw;
accessMode = "write";
bitsWritten = 0;
try {
fw = new FileOutputStream(fileName);
out = new DataOutputStream(fw);
} catch (IOException e) {
System.out.println("Error opening output file " + fileName);
}
}
}
/**
* Writes a character to the output file
*
* @param bit
* Bit to write to the output file
*/
public void writeBit(char bit) {
int b;
try {
// Convert the character "bit" to a bit. Bits are stored in "buffer"
if (bit == '0')
buffer = (char) (2 * (int) buffer);
else
buffer = (char) (2 * (int) buffer + 1);
b = buffer;
++bitsWritten;
if (bitsWritten == 8) {
out.write(buffer);
bitsWritten = 0;
buffer = 0;
}
} catch (IOException e) {
System.out.println("Error writing to output file");
}
}
/**
* Reads the next bit from the input file. If all the bits have been read
* this method returns EOF. Bit returned is first converted to a char, so
* this method returns a bit as either '0' or '1'.
*
* @return Next bit from the input file or EOF if there are no more bits in
* it.
*/
public char readBit() {
char c = 0;
if (bitsRead == 8)
try {
if (in.available() > 0) { // We have not reached the end of the
// file
buffer = (char) in.read();
bitsRead = 0;
} else
return 0;
} catch (IOException e) {
System.out.println("Error reading from file ");
System.exit(0); // Terminate the program
}
// return next bit from the buffer; bit is converted first to char
if ((buffer & 128) == 0)
c = '0';
else
c = '1';
buffer = (char) (buffer << 1);
++bitsRead;
return c;
}
/**
* Close the file to ensure that no information is lost.
*/
public void close() {
String padding = "01110010";
try {
if (accessMode.equals("read"))
in.close();
else {
int i = 0;
int b;
while (bitsWritten < 8) {
buffer = (char) (buffer << 1);
b = buffer;
if (padding.charAt(i) == '1')
buffer = (char) (buffer + 1);
b = buffer;
++i;
++bitsWritten;
}
out.write(buffer);
out.close();
}
} catch (IOException e) {
System.out.println("Error closing file ");
System.exit(0); // Terminate the program
}
}
}