Java - Ayuda con calculadora

Hola, es mi primera calculadora y tengo como sumar, restar, borrar valores, boton de igual, pero e estado intentando poner que multiplique y no me funciona mi logica. Alguine podria explicarme o ayudarme con el codigo? Muchas gracias

La logica funciona asi, cuando le picas a cierto boton de sumar o restar manda los datos de la pantaya a una memoria y luego lo suma y lo mismo con restar.

[code]
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Tare extends JApplet implements ActionListener {
private JTextField displayField;
private JButton bd,b1,b2,b3,b4,b5,b6,b7,b8,b9,bm,bn,bmult,bi,C,b0;
int memoria=0;
private String result="";
int signo=1;
public void init()
{
Container container = getContentPane();
container.setLayout( new FlowLayout() );

displayField = new JTextField( 15 );
displayField.setEditable( true );
container.add( displayField );

b0 = new JButton( "0" );
container.add( b0 );
b0.addActionListener( this );
b1 = new JButton( "1" );
container.add( b1 );
b1.addActionListener( this );
b2 = new JButton( "2" );
container.add( b2 );
b2.addActionListener( this );
b3 = new JButton( "3" );
container.add( b3 );
b3.addActionListener( this );
b4 = new JButton( "4" );
container.add( b4 );
b4.addActionListener( this );
b5 = new JButton( "5" );
container.add( b5 );
b5.addActionListener( this );
b6 = new JButton( "6" );
container.add( b6 );
b6.addActionListener( this );
b7 = new JButton( "7" );
container.add( b7 );
b7.addActionListener( this );
b8 = new JButton( "8" );
container.add( b8 );
b8.addActionListener( this );
b9 = new JButton( "9" );
container.add( b9 );
b9.addActionListener( this );
bn = new JButton( "-" );
container.add( bn );
bn.addActionListener( this );
bm = new JButton( "+" );
container.add( bm );
bm.addActionListener( this );
bmult = new JButton( "*" );
container.add( bmult );
bd = new JButton( "/" );
container.add( bd );
bd.addActionListener( this );
bmult.addActionListener( this );
bi = new JButton( "=" );
container.add( bi );
bi.addActionListener( this );
C = new JButton( "C" );
container.add( C );
C.addActionListener( this );

}
public void actionPerformed( ActionEvent event )
{
if ( event.getSource() == b0 )
addnumber("0");
if ( event.getSource() == b1 )
addnumber("1");
else if ( event.getSource() == b2 )
addnumber("2");
else if ( event.getSource() == b3 )
addnumber("3");
else if ( event.getSource() == b4 )
addnumber("4");
else if ( event.getSource() == b5 )
addnumber("5");
else if ( event.getSource() == b6 )
addnumber("6");
else if ( event.getSource() == b7 )
addnumber("7");
else if ( event.getSource() == b8 )
addnumber("8");
else if ( event.getSource() == b9 )
addnumber("9");
else if ( event.getSource() == bm )
suma("+");
else if ( event.getSource() == bn )
suma("-");
else if ( event.getSource() == bmult )
mult();
else if ( event.getSource() == bd )
suma("/");
else if ( event.getSource() == bi )
igual();
else if ( event.getSource() == C )
borrar();
}
public void mult(){

}
public void borrar()
{
displayField.setText("");
memoria=0;
result=""+memoria;
displayField.setText (result);
}
public void addnumber(String result1)
{
result= result+result1;
displayField.setText (result);
}
public void suma(String simbolo){

displayField.setText("+");

memoria+=Integer.parseInt(result)*signo;
result="";
displayField.setText (result);
if (simbolo=="-")
{
signo=(-1);
}
else{signo=(+1);}

}
public void igual()
{
memoria+=Integer.parseInt(result)*signo;
result=memoria+"";
displayField.setText (result);
memoria=0;
signo=1;
}
}
[/code]