缓冲流有关问题 (ByteArrayInputStream/DataInputStream)

缓冲流问题 (ByteArrayInputStream/DataInputStream)
import java.io.*;
public class TestBuffer2{
public static void main(String args [])throws Exception{
ByteArrayOutputStream bos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(bos);
dos.writeInt(1);
dos.writeUTF("HELLO");

byte [] buf = new byte [1024];
ByteArrayInputStream bis = new ByteArrayInputStream(buf);
DataInputStream dis = new DataInputStream(bis);
System.out.println(dis.readInt());
System.out.println(dis.readUTF());

dos.flush();
dos.close();
dis.close();
}
}
为什么 读出的数据居然是 0 和空(什么都没有 一些空行)呢 请大虾们帮帮忙了

[解决办法]
API

Java code

public ByteArrayOutputStream() {    this(32);}public ByteArrayOutputStream(int size) {        if (size < 0) {            throw new IllegalArgumentException("Negative initial size: "                                               + size);        }    buf = new byte[size];    }