need help displaying hex values
Below is a program which loads a file and then displays a binary representation of its contents. I need to modify it to display the hex representation. I think I understand most of the code, but I don't get what the following excerpt is about:
value = value << 1;
if (bit == '1')
value = value | mask;
which is found in the writebit() method in the code below. Could anyone help me to understand this? Am I right to assume that modifying this chunk is the key to solving this problem?
Code:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class Exercise19_20 extends JFrame {
private JTextField jtfFilename = new JTextField();
private JButton jbtSave = new JButton("Save the bits to the file");
private JTextArea jtaBits = new JTextArea();
public Exercise19_20() {
JPanel panel1 = new JPanel(new BorderLayout());
panel1.add(new JLabel("Enter a file"), BorderLayout.WEST);
panel1.add(jtfFilename, BorderLayout.CENTER);
add(panel1, BorderLayout.NORTH);
jtaBits.setLineWrap(true);
add(new JScrollPane(jtaBits));
add(jbtSave, BorderLayout.SOUTH);
jtfFilename.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try {
FileInputStream in = new FileInputStream(jtfFilename.getText().trim());
String s = "";
int value;
while ((value = in.read()) != -1) {
s += getBits(value);
}
in.close();
jtaBits.setText(s);
}
catch (IOException ex) {
ex.printStackTrace();
}
}
});
jbtSave.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try {
BitOutputStream output = new BitOutputStream(new File(jtfFilename.getText().trim()));
output.writeBit(jtaBits.getText().trim());
output.close();
}
catch (IOException ex) {
ex.printStackTrace();
}
}
});
}
public static String getBits(int value) {
String result = "";
int mask = 1;
for (int i = 7; i >= 0; i--) {
int temp = value >> i;
int bit = temp & mask;
result = result + bit;
}
return result;
}
public static class BitOutputStream {
private FileOutputStream output;
private int value;
private int count = 0;
private int mask = 1; // The bits are all zeros except the last one
public BitOutputStream(File file) throws IOException {
output = new FileOutputStream(file);
}
public void writeBit(char bit) throws IOException {
count++;
value = value << 1;
if (bit == '1')
value = value | mask;
if (count == 8) {
output.write(value);
count = 0;
}
}
public void writeBit(String bitString) throws IOException {
for (int i = 0; i < bitString.length(); i++)
writeBit(bitString.charAt(i));
}
/** Write the last byte and close the stream. If the last byte is not full, right-shfit with zeros */
public void close() throws IOException {
if (count > 0) {
value = value << (8 - count);
output.write(value);
}
output.close();
}
}
/** Main method */
public static void main(String[] args) {
JFrame frame = new Exercise19_20();
frame.setTitle("Exercise19_20");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(400, 400);
frame.setLocationRelativeTo(null); // Center the frame
frame.setVisible(true);
}
}
Thanks for any help
