java ，我把文字输出到图片上（验证码），不过文字好小啊！该怎么办，下图

Question

诸君请看，这个是图，我想让这个字变得更加的大，应该要怎么做呢？下面是代码
import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;

public class CheckingCode
{
int width = 200 ;
int height = 140 ;
BufferedOutputStream bos = null ;
Random ran ;
BufferedImage bi ;
Graphics gra ;
StringBuilder sb ;

public void doPost ()
{
    String code = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789" ;

    sb = new StringBuilder ("") ;
    ran = new Random () ;

    bi = new BufferedImage (width,height,BufferedImage.TYPE_INT_RGB) ;
    gra = bi.getGraphics() ;
    gra.setColor(Color.white) ;
    gra.fillRect(0,0,width,height) ;

    for(int i = 0 ; i < 4 ; i ++)
    {
        Character ch = code.charAt(ran.nextInt(code.length()+1)) ;
        sb.append(ch) ;
        gra.setColor(Color.BLACK) ;
        gra.drawString(ch.toString(),25*i+30,70) ;  
    }
    try 
    {
        bos = new BufferedOutputStream (new FileOutputStream (new File ("image//1.jpg"))) ;
        ImageIO.write(bi,"jpg",bos) ;
    } 
    catch (IOException e) 
    {
            // TODO Auto-generated catch block
        e.printStackTrace();
    }
    finally
    {
        try
        {
            if(bos!=null)
            bos.close() ;
        } 
        catch (IOException e) 
        {
                // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}
public CheckingCode () 
{
    doPost () ;
}
public static void main(String[] args) 
{
    // TODO Auto-generated method stub
    new CheckingCode () ;
}

}
只要改包名就可以了。
如果太麻烦的话，只需要给些小hints给我就好了：》不用特意写一段给我：》（当然如果写了我也会笑纳的）

Answer 1

gra.setFont(new Font("宋体",Font.BOLD,30)); //设置字体