/***********************************************************
   Shifts.java							    

   COMP 111

This applet is intended to illustrate how 
bitwise operations can be used to
reveal the binary representation of a number.

***********************************************************/


// imported packages
import java.applet.*;
import java.awt.*;

// Shifts applet
// -----------
public class Shifts extends Applet {

    int value;

    Button shiftLeft;
    Button shiftRight;
    
    TextField display;
    TextField entry;


    // layout
    // 
    // +------------------+
    // |     |entry|      |
    // |      -----       |
    // |    __     __     |
    // |   |<<|   |>>|    |
    // |    --     --     |
    // |  ______________  |
    // | |  display     | |
    // |  --------------  |
    // +------------------+
    public void init() {
	resize(400,300);

	setLayout(new GridLayout(3,1,5,5));

	value = 0;
	entry   = new TextField("", 12);
	entry.setText(String.valueOf(value));
	display = new TextField("", 35);
	display.setEditable(false);
	display.setText(toBinaryString(value));
	shiftLeft = new Button("<<");
	shiftRight = new Button(">>");

	Panel p1 = new Panel();
	p1.add(entry);
	Panel p2 = new Panel();
	p2.add(shiftLeft);
	p2.add(shiftRight);
	Panel p3 = new Panel();
	p3.add(display);
	add(p1);
	add(p2);
	add(p3);
    }


    // method to convert text in entry field to an integer value
    private void readVal() {
	Integer i = Integer.valueOf(entry.getText());
	value = i.intValue();
    }
	

    // update the display to match the entry
    private void update() {
	entry.setText(String.valueOf(value));
	display.setText(toBinaryString(value));
	repaint();
    }


    public boolean action(Event e, Object arg) {
	if (e.target == shiftLeft) 
	    value = value << 1;
	else if (e.target == shiftRight) 
	    value = value >> 1;
	else
	    readVal();
	update();
	return true;
    }
    

    // checks if kth bit in (32-bit) binary representation of
    // integer n is on (i.e., 1)
    public boolean isKthBitOn(int n, int k) {
	if (k < 1) 
	    return false;
	else {
	    int i = n & (1 << (k-1));
	    return (i != 0);
	}
    }

    // convert kth bit in (32-bit) binary representation of
    // integer n to string ("0" or "1")
    public String kthBit(int i, int k) {
	if (isKthBitOn(i, k)) 
	    return "1";
	else
	    return "0";
    }


    // convert integer i to a String revealing its 
    // (32-bit) binary representation 
    public String toBinaryString(int i) {
	String s = "";
	int k = 1;

	// bits 1-8
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;

	// bits 9-16
	s = " " + s;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;

	// bits 17-24
	s = " " + s;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;

	// bits 25-32
	s = " " + s;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;
	k = k + 1;
	s = kthBit(i,k) + s;

	return s;
    }
}