자바 배열에대해 질문드립니다.

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
 
public class Base extends Applet
{
Label display;
		Button []button;
		TextArea ta;
		Panel p1;
		public void init()
		{
				setLayout(new BorderLayout());
				display = new Label("game");
				display.setAlignment(Label.RIGHT);
				add("North", display);
				p1 = new Panel();
				p1.setLayout(new GridLayout(4,3));
				for(int i = 0; i<9; i++)
				{
						button[i] = new Button(String.valueOf(i+1));
						p1.add(button[i]);
				}
				button[9] = new Button("<-");
				p1.add(button[9]);
				button[10] = new Button("다시입력");
				p1.add(button[10]);
				button[11] =new Button("입력완료");
				p1.add(button[11]);
				add("Center", p1);
 
				ta = new TextArea(10, 20);
				add("South", ta);
		}
}