PipedReader与PipedWriter有哪些不同的地方

package java.io; public class PipedWriter extends Writer {   // 与PipedWriter通信的PipedReader对象   private PipedReader sink;   // PipedWriter的关闭标记   private boolean closed = false;   // 构造函数，指定配对的PipedReader   public PipedWriter(PipedReader snk) throws IOException {     connect(snk);   }   // 构造函数   public PipedWriter() {   }   // 将“PipedWriter” 和 “PipedReader”连接。   public synchronized void connect(PipedReader snk) throws IOException {     if (snk == null) {       throw new NullPointerException();     } else if (sink != null || snk.connected) {       throw new IOException("Already connected");     } else if (snk.closedByReader || closed) {       throw new IOException("Pipe closed");     }     sink = snk;     snk.in = -1;     snk.out = 0;     // 设置“PipedReader”和“PipedWriter”为已连接状态     // connected是PipedReader中定义的，用于表示“PipedReader和PipedWriter”是否已经连接     snk.connected = true;   }   // 将一个字符c写入“PipedWriter”中。   // 将c写入“PipedWriter”之后，它会将c传输给“PipedReader”   public void write(int c) throws IOException {     if (sink == null) {       throw new IOException("Pipe not connected");     }     sink.receive(c);   }   // 将字符数组b写入“PipedWriter”中。   // 将数组b写入“PipedWriter”之后，它会将其传输给“PipedReader”   public void write(char cbuf[], int off, int len) throws IOException {     if (sink == null) {       throw new IOException("Pipe not connected");     } else if ((off | len | (off + len) | (cbuf.length - (off + len))) < ) {       throw new IndexOutOfBoundsException();     }     sink.receive(cbuf, off, len);   }   // 清空“PipedWriter”。   // 这里会调用“PipedReader”的notifyAll()；   // 目的是让“PipedReader”放弃对当前资源的占有，让其它的等待线程(等待读取PipedWriter的线程)读取“PipedWriter”的值。   public synchronized void flush() throws IOException {     if (sink != null) {       if (sink.closedByReader || closed) {         throw new IOException("Pipe closed");       }       synchronized (sink) {         sink.notifyAll();       }     }   }   // 关闭“PipedWriter”。   // 关闭之后，会调用receivedLast()通知“PipedReader”它已经关闭。   public void close() throws IOException {     closed = true;     if (sink != null) {       sink.receivedLast();     }   } }