Java.io package Useful Resources
Java.io - Discussion

Java - PipedReader class

Quiz

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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