Java - PushbackReader read(char[] cbuf,int off,int len) method

---

---

Description

The Java PushbackReader read(char[] cbuf,int off,int len) method reads characters into a portion of an array.

read(char[] cbuf,int off,int len) method −

• Reads characters into a portion of a character array

• Returns the number of characters actually read, or -1 if end of stream.

Declaration

Following is the declaration for java.io.PushbackReader.read(char[] cbuf,int off,int len) method.

public int read(char[] cbuf,int off,int len)

Parameters

• cbuf − Destination buffer.

• off − Offset at which to start writing characters.

• len − Maximum number of characters to read.

Return Value

This method returns The number of characters read, or -1 if the end of the stream has been reached.

Exception

IOException − If an I/O error occurs.

Example - Usage of PushbackReader read(char[] cbuf,int off,int len) method

The following example shows the usage of PushbackReader read(char[] cbuf,int off,int len) method.

PushbackReaderDemo.java

package com.tutorialspoint;

import java.io.IOException;
import java.io.PushbackReader;
import java.io.StringReader;

public class PushbackReaderDemo {
   public static void main(String[] args) {
      String s = "Hello World";

      // create a new StringReader
      StringReader sr = new StringReader(s);

      // create a new PushBack reader based on our string reader
      PushbackReader pr = new PushbackReader(sr, 20);

      // create a char array to read chars into
      char cbuf[] = new char[5];

      try {
         // read characters into an array.
         System.out.println("" + pr.read(cbuf));

         // print cbuf
         System.out.println(cbuf);

         // Close the stream 
         pr.close();

      } catch (IOException ex) {
         ex.printStackTrace();
      }
   }
}

Output

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

5
Hello

Example - Basic use of read(char[], int, int)

The following example shows the usage of PushbackReader read(char[] cbuf,int off,int len) method.

PushbackReaderDemo.java

package com.tutorialspoint;

import java.io.IOException;
import java.io.PushbackReader;
import java.io.StringReader;

public class PushbackReaderDemo {
   public static void main(String[] args) {
      try (PushbackReader reader = new PushbackReader(new StringReader("HelloWorld"))) {
         char[] buffer = new char[10];

         // Read 5 characters starting at index 2 in the array
         int charsRead = reader.read(buffer, 2, 5);

         System.out.println("Characters read: " + charsRead);
         System.out.print("Buffer content: ");
         for (char c : buffer) {
            System.out.print(c == '\u0000' ? '_' : c); // Print underscores for unused
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Characters read: 5  
Buffer content: __Hello____

Explanation

• Reads 5 characters ("Hello") into the array starting from index 2.

• Other parts of the array remain with default \u0000 (null characters).

Example - Using read() after unread()

The following example shows the usage of PushbackReader read(char[] cbuf,int off,int len) method.

PushbackReaderDemo.java

package com.tutorialspoint;

import java.io.IOException;
import java.io.PushbackReader;
import java.io.StringReader;

public class PushbackReaderDemo {
   public static void main(String[] args) {
      // Set pushback buffer size to 6 (more than 3 needed)
      try (PushbackReader reader = new PushbackReader(new StringReader("Stream"), 6)) {
         char[] buffer = new char[6];
   
         // Read first 3 characters: 'S', 't', 'r'
         int read1 = reader.read(buffer, 0, 3);
         System.out.println("First read: " + new String(buffer, 0, read1)); // Str

         // Unread the same 3 characters
         reader.unread(buffer, 0, read1);

         // Read up to 6 characters again
         int read2 = reader.read(buffer, 0, 6);
         System.out.println("After unread, read again: " + new String(buffer, 0, read2)); // Stream
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

First read: Str  
After unread, read again: Strea

Explanation

• Reads "Str" into the buffer.

• Then unreads it, placing it back into the stream.

• Reads again − this time it continues beyond the previous read.