Java – PipedWriter

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PipedWriter is a Java class that is used to write data to a PipedInputStream. It is a character-oriented output stream that is typically used for inter-thread communication.

When you write data to a PipedWriter, the data is sent to a connected PipedInputStream. This is useful when you have two threads that need to communicate with each other. One thread can write data to the PipedWriter, and the other thread can read that data from the connected PipedInputStream.

Here’s an example that demonstrates how to use PipedWriter and PipedInputStream:

import java.io.*;

public class Example {
  public static void main(String[] args) throws Exception {
    PipedWriter writer = new PipedWriter();
    PipedInputStream reader = new PipedInputStream(writer);

    Thread writerThread = new Thread(() -> {
      try {
        writer.write("Hello, world!");
        writer.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    });

    Thread readerThread = new Thread(() -> {
      try {
        int data;
        while ((data = reader.read()) != -1) {
          System.out.print((char) data);
        }
        reader.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    });

    writerThread.start();
    readerThread.start();

    writerThread.join();
    readerThread.join();
  }
}

In this example, we create a PipedWriter and a PipedInputStream. We pass the PipedWriter to the PipedInputStream constructor to create a connection between them.

We then create two threads. One thread writes “Hello, world!” to the PipedWriter and then closes it. The other thread reads from the connected PipedInputStream and prints out the data it reads.

We start both threads, and then wait for them to finish using the join() method. When both threads have finished, the program terminates.

Constructor:

The PipedWriter class provides several constructors to create a new PipedWriter object:

  1. PipedWriter(): creates a new PipedWriter with the default pipe size (1024 bytes).
  2. PipedWriter(int pipeSize): creates a new PipedWriter with the specified pipe size. The pipeSize parameter specifies the size of the pipe buffer, in bytes. A larger buffer allows more data to be stored in the pipe before blocking occurs.
  3. PipedWriter(PipedInputStream snk): creates a new PipedWriter that is connected to the specified PipedInputStream. Any data written to this PipedWriter is automatically sent to the connected PipedInputStream.
  4. PipedWriter(PipedInputStream snk, boolean isDaemon): creates a new PipedWriter that is connected to the specified PipedInputStream. The isDaemon parameter specifies whether the thread that reads from the connected PipedInputStream is a daemon thread. If true, the thread is a daemon thread and will not prevent the JVM from exiting if it is the only thread running.

Here’s an example that shows how to create a new PipedWriter using the default constructor:

PipedWriter writer = new PipedWriter();

This creates a new PipedWriter with the default pipe size of 1024 bytes.

And here’s an example that shows how to create a new PipedWriter that is connected to a PipedInputStream:

PipedInputStream reader = new PipedInputStream();
PipedWriter writer = new PipedWriter(reader);

This creates a new PipedInputStream and a new PipedWriter that is connected to the PipedInputStream. Any data written to the PipedWriter will be automatically sent to the PipedInputStream.

Method:

The PipedWriter class provides several methods for writing data to the connected PipedInputStream:

  1. void write(int c) throws IOException: writes a single character to the PipedWriter.
  2. void write(char[] cbuf) throws IOException: writes an array of characters to the PipedWriter.
  3. void write(char[] cbuf, int off, int len) throws IOException: writes a portion of an array of characters to the PipedWriter.
  4. void write(String str) throws IOException: writes a string to the PipedWriter.
  5. void write(String str, int off, int len) throws IOException: writes a portion of a string to the PipedWriter.
  6. void flush() throws IOException: flushes the output buffer to the connected PipedInputStream.
  7. void close() throws IOException: closes the PipedWriter and the connected PipedInputStream.

Here’s an example that demonstrates how to use the write() method to write data to a PipedInputStream:

import java.io.*;

public class Example {
  public static void main(String[] args) throws Exception {
    PipedWriter writer = new PipedWriter();
    PipedInputStream reader = new PipedInputStream(writer);

    writer.write("Hello, world!");
    writer.close();

    int data;
    while ((data = reader.read()) != -1) {
      System.out.print((char) data);
    }
    reader.close();
  }
}

In this example, we create a PipedWriter and a PipedInputStream, and connect them. We then write the string “Hello, world!” to the PipedWriter using the write() method, and close the writer.

We then read from the connected PipedInputStream using the read() method, and print out the data we read. Finally, we close the PipedInputStream.

Example:

Here’s an example that demonstrates how to use PipedWriter and PipedInputStream to implement inter-thread communication in Java:

import java.io.*;

public class Example {
  public static void main(String[] args) throws Exception {
    PipedWriter writer = new PipedWriter();
    PipedInputStream reader = new PipedInputStream(writer);

    Thread writerThread = new Thread(() -> {
      try {
        writer.write("Hello, world!");
        writer.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    });

    Thread readerThread = new Thread(() -> {
      try {
        int data;
        while ((data = reader.read()) != -1) {
          System.out.print((char) data);
        }
        reader.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    });

    writerThread.start();
    readerThread.start();

    writerThread.join();
    readerThread.join();
  }
}

In this example, we create a PipedWriter and a PipedInputStream, and connect them. We then create two threads: one thread writes the string “Hello, world!” to the PipedWriter and closes it, while the other thread reads from the connected PipedInputStream and prints out the data it reads.

We start both threads using the start() method, and wait for them to finish using the join() method. When both threads have finished, the program terminates.

Note that this is just a simple example to demonstrate the usage of PipedWriter and PipedInputStream. In practice, you would typically use higher-level abstractions such as the java.util.concurrent package to implement inter-thread communication in a more robust and efficient way.