Calculator program without using ActionListener

/*
<applet code="Calculator.class" height =200 width=200>
</applet>
*/

import java.awt.*;
import java.applet.*;
import java.awt.event.*;
public class Calculator extends Applet
{
String first,op;
TextField t1;
Button b1,b2,b3,b4,b5,b6,b7,b8,b9,b10,b11,b12,b13,b15,b14,b0;
public void init()
{
t1=new TextField(40);
b0=new Button("0");
b1=new Button("1");
b2=new Button("2");
b3=new Button("3");
b4=new Button("4");
b5=new Button("5");
b6=new Button("6");
b7=new Button("7");
b8=new Button("8");
b9=new Button("9");
b10=new Button("+");
b11=new Button("-");
b12=new Button("*");
b13=new Button("/");
b14=new Button(".");
b15=new Button("=");
Panel p=new Panel();

p.setLayout(new GridLayout(4,4));


p.add(b0); p.add(b1);
p.add(b2); p.add(b3);
p.add(b4); p.add(b5);
p.add(b6); p.add(b7);
p.add(b8); p.add(b9);
p.add(b10); p.add(b11);
p.add(b12); p.add(b13);
p.add(b14); p.add(b15);

Panel p1=new Panel();
p1.setLayout(new BorderLayout());
p1.add("North",t1);
p1.add("Center",p);
add(p1);
}

public boolean action(Event e,Object o)

{

if(o.equals("0"))

t1.setText(t1.getText()+"0");

if(o.equals("1"))

t1.setText(t1.getText()+"1");

if(o.equals("2"))

t1.setText(t1.getText()+"2");

if(o.equals("3"))

t1.setText(t1.getText()+"3");

if(o.equals("4"))

t1.setText(t1.getText()+"4");

if(o.equals("5"))

t1.setText(t1.getText()+"5");

if(o.equals("6"))

t1.setText(t1.getText()+"6");

if(o.equals("7"))

t1.setText(t1.getText()+"7");

if(o.equals("8"))

t1.setText(t1.getText()+"8");

if(o.equals("9"))

t1.setText(t1.getText()+"9");

if(o.equals("."))

t1.setText(t1.getText()+".");

if(o.equals("+"))

{

first=t1.getText();

op="+";

t1.setText("");

}

if(o.equals("-"))

{

first=t1.getText();

op="-";

t1.setText("");

}

if(o.equals("*"))

{

first=t1.getText();

op="*";

t1.setText("");

}

if(o.equals("/"))

{

first=t1.getText();

op="/";

t1.setText("");

}

if(o.equals("="))

{

float x=Float.parseFloat(first);

float y=Float.parseFloat(t1.getText());

float z=0.0f;

if(op.equals("+"))

{

z=x+y;

}

if(op.equals("-"))

{

z=x-y;

}

if(op.equals("*"))

{

z=x*y;

}

if(op.equals("/"))

{

z=x/y;

}

t1.setText(""+z);

}

return true;

}

}