Why is my java program not running ?

here's a java program with awt taught in our college .

import java.awt.*;

import java.awt.event.*;

public class FrameDemo2 extends Frame implements ActionListener{

FrameDemo2(String s)

{

super(s);

}

Label lbl1,lbl2;

TextField txt1,txt2;

Button b1,b2;

setLayout(new GridLayout(3,2));

public void initialize()

{

lbl1 = new Label("Enter number : ");

lbl2 = new Label("Result");

txt1 = new TextField(10);

txt2 = new TextField(20);

b1=new Button("Square ");

b2=new Button("Clear");

add(lbl1);

add(txt1);

add(lbl2);

add(txt2);

add(b1);

add(b2);

b1.addActionListener(this);

b2.addActionListener(this);

}

public void actionPerformed(ActionEvent e)

{

if(e.getSource()==b1)

{

int no;

double d1;

no = Integer.parseInt(txt1.getText());

d1=Math.pow(no,2);

txt2.setText(""+d1);

}

if(e.getSource()==b2)

{

txt1.setText("");

txt2.setText("");

}

}

}

class Vclient

{

public static void main(String[] args)

{

FrameDemo2 fd2 = new FrameDemo2("Action");

fd2.setSize(400,450);

fd2.initialize();

fd2.setVisible(true);

}

}

i get an error when i try to set layout , using setLayout method . The error says invalid method declaration . return type required .

But if i write fd2.setLayout(new GridLayout(3,2)); then the program works .

Can anyone explain why is it happening like that ??