Java Code

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Bin2Dec extends JApplet implements ActionListener 
{
	JTextField binaryNum;
	JLabel label, dec;
	JButton go;
	public void init( )
	{
		setLayout( new FlowLayout( ) );
		label = new JLabel( "Enter a binary number" );
		binaryNum = new JTextField( 10 );
		dec = new JLabel( "" );
		go = new JButton( "convert" );
		go.addActionListener( this );
		add( label );	add( binaryNum );
		add( go );	add( dec );
	}
	public void actionPerformed( ActionEvent ae )
	{
		String bin = binaryNum.getText( );
		int numBits = bin.length( );
		int power = numBits - 1;
		int sum = 0;
		for( int i=0; i<numBits; i++ )
		{
			int bit = Integer.parseInt( bin.substring( i, i+1 ) );
			int term = (int)(bit * Math.pow( 2, power ));
			sum += term;
			power--;
		}
		dec.setText( String.valueOf( sum ) );
	}
}