请问各位大佬，这个代码对于一定字节以上的文件为何会导致输出文件相当大（能达到1个多G）

[Queen_ZiLuoHeng]

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class CopyDemo01 {
public static void copyImageFile(String filepath,String targetpath) {
try {
FileInputStream fis = new FileInputStream(filepath);
BufferedInputStream bis= new BufferedInputStream(fis);
FileOutputStream fos = new FileOutputStream(targetpath);
BufferedOutputStream bos = new BufferedOutputStream(fos);
int len = 0;
byte[] b = new byte[2048];
try {

while((len = bis.read(b))!=-1) {
bos.write(b,0,len);
}
bis.close();
bos.close();
} catch (IOException e) {
e.printStackTrace();
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}

public static void main(String[] args) {
copyImageFile("icon.png","copyIcon.png");
}

}

[yjsl__]

可以在while循环里输出循环次数，计算一下应当循环几次