Java - PipedReader class

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Introduction

The Java PipedReader class represents piped character-input streams.

Class declaration

Following is the declaration for Java.io.PipedReader class −

 public class PipedReader extends Reader

Field

Following are the fields for Java.io.PipedReader class −

  • protected Object lock − This is the object used to synchronize operations on this stream.

Class constructors

Sr.No. Constructor & Description
1

PipedReader()

This creates a PipedReader so that it is not yet connected.
2

PipedReader(int pipeSize)

This creates a PipedReader so that it is not yet connected and uses the specified pipe size for the pipe's buffer.
3

PipedReader(PipedWriter src)

This creates a PipedReader so that it is connected to the piped writer src.
4

PipedReader(PipedWriter src, int pipeSize)

This creates a PipedReader so that it is connected to the piped writer src and uses the specified pipe size for the pipe's buffer.

Class methods

Sr.No. Method & Description
1 void close()

This method closes this piped stream and releases any system resources associated with the stream.
2 void connect(PipedWriter src)

This method causes this piped reader to be connected to the piped writer src.
3 int read()

This method reads the next character of data from this piped stream.
4 int read(char[] cbuf, int off, int len)

This method reads up to len characters of data from this piped stream into an array of characters.
5 boolean ready()

This method tell whether this stream is ready to be read.

Methods inherited

This class inherits methods from the following classes −

  • Java.io.Reader
  • Java.io.Object

Example - Closing a PipedReader after reading from a connected PipedWriter

The following example shows the usage of PipedReader close() method.

PipedReaderDemo.java

 package com.tutorialspoint; import java.io.PipedReader; import java.io.PipedWriter; import java.io.IOException; public class PipedReaderDemo { public static void main(String[] args) { try { PipedReader reader = new PipedReader(); PipedWriter writer = new PipedWriter(reader); // Connect streams writer.write("Hello, Reader!"); writer.close(); // Finish writing int data; while ((data = reader.read()) != -1) { System.out.print((char) data); } reader.close(); // Close the reader after reading is complete System.out.println("\nPipedReader closed successfully."); } catch (IOException e) { e.printStackTrace(); } } }

Output

Let us compile and run the above program, this will produce the following result−

 Hello, Reader! PipedReader closed successfully.

Explanation

  • The close() method is used to release system resources held by the PipedReader.

  • After the data is fully read, closing the stream is necessary to avoid resource leaks.

  • Always close both ends (PipedReader and PipedWriter) when done.

Example - Connecting PipedReader to PipedWriter and reading text

The following example shows the usage of PipedReader connect(PipedWriter src) method.

PipedReaderDemo.java

 package com.tutorialspoint; import java.io.PipedReader; import java.io.PipedWriter; import java.io.IOException; public class PipedReaderDemo { public static void main(String[] args) { try { PipedReader reader = new PipedReader(); PipedWriter writer = new PipedWriter(); // Connect the reader to the writer reader.connect(writer); // Write data through the writer writer.write("Hello from PipedWriter!"); writer.close(); // Close to signal end of data // Read and print data from reader int data; while ((data = reader.read()) != -1) { System.out.print((char) data); // Output: Hello from PipedWriter! } reader.close(); } catch (IOException e) { e.printStackTrace(); } } }

Output

Let us compile and run the above program, this will produce the following result−

 Hello from PipedWriter!

Explanation

  • The connect(PipedWriter src) method connects the PipedReader to the given PipedWriter.

  • Once connected, data written to the PipedWriter can be read from the PipedReader.

  • This is a basic example of one-way character communication between two objects in the same thread.

Example - Reading single characters using read() after connecting to PipedWriter

The following example shows the usage of PipedReader read() method.

PipedReaderDemo.java

 package com.tutorialspoint; import java.io.PipedReader; import java.io.PipedWriter; import java.io.IOException; public class PipedReaderDemo { public static void main(String[] args) { try { PipedReader reader = new PipedReader(); PipedWriter writer = new PipedWriter(reader); // Connect via constructor writer.write("ABC"); writer.close(); // Finish writing int ch; while ((ch = reader.read()) != -1) { System.out.print((char) ch); // Output: ABC } reader.close(); } catch (IOException e) { e.printStackTrace(); } } }

Output

Let us compile and run the above program, this will produce the following result−

 ABC

Explanation

  • The read() method reads one character at a time (as an int) and returns -1 when the stream ends.

  • This example demonstrates synchronous reading of characters written to a pipe.

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