Java基础知识之ByteArrayInputStream流的使用

 
    protected byte buf[];
 
    
    protected int pos;
 
    
    protected int mark = 0;
 
    
    protected int count;

 
    public ByteArrayInputStream(byte buf[]) {
        this.buf = buf;
        this.pos = 0;
        this.count = buf.length;
    } 
    
    public ByteArrayInputStream(byte buf[], int offset, int length) {
        this.buf = buf;
        this.pos = offset;
        this.count = Math.min(offset + length, buf.length);
        this.mark = offset;
    }

 
    public synchronized int read() {
        return (pos < count) ? (buf[pos++] & 0xff) : -1;
    }

   
    public synchronized int read(byte b[], int off, int len) {
        if (b == null) {
            throw new NullPointerException();
        } else if (off < 0 || len < 0 || len > b.length - off) {
            throw new IndexOutOfBoundsException();
        }
 
        if (pos >= count) {
            return -1;
        }
 
        int avail = count - pos;
        if (len > avail) {
            len = avail;
        }
        if (len <= 0) {
            return 0;
        }
        System.arraycopy(buf, pos, b, off, len);
        pos += len;
        return len;
    }

    
    public void close() throws IOException {
    }

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
public class Test4 {
 //ByteArrayInputStream本身操作的是一个数组，并没有打开文件描述之类的，所有不需要关闭流
 
 public static void main(String[] args) {
  ByteArrayInputStream bais=null;
  StringBuilder sb=new StringBuilder();
  int temp=0;
  int num=0;
  long date1=System.currentTimeMillis();
  try{
   byte[] b="abcdefghijklmnopqstuvxyz".getBytes();
   //从字符数组b中读取数据，从下标为2开始计数读8个
   bais=new ByteArrayInputStream(b,2,8);
   while((temp=bais.read())!=-1){
    sb.append((char)temp);
    num++;
   }
      System.out.println(sb);
      System.out.println("读取的字节数："+num);
  }finally{
   try{
    bais.close();//不需要关闭流的，但是调用close没有任何影响，close不做任何事情
   }catch(IOException e){
    e.printStackTrace();
   }
   new File("d:"+File.separator+"a.txt");//File.separator是一个文件分隔符，在windows和linux平台下运行都没有问题
  }
  long date2=System.currentTimeMillis();
  System.out.println("耗时:"+(date2-date1)); 
 } 
}