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

---

---

Description

The Java Reader read(char[] cbuf,int off,int len) method reads characters into a portion of an array. This method will block until some input is available, an I/O error occurs, or the end of the stream is reached.

Declaration

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

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

Parameters

• cbuf − Destination buffer.

• off − Offset at which to start storing 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 some I/O error occurs.

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

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

ReaderDemo.java

package com.tutorialspoint;

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

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

      // create a StringReader
      Reader reader = new StringReader(s);

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

      try {
         // read characters into a portion of an array.
         System.out.println( reader.read(cbuf, 0, 5));

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

         // close the stream 
         reader.close();

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

Output

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

5
Hello

Example - Reading into a portion of a character array

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

ReaderDemo.java

package com.tutorialspoint;

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

public class ReaderDemo {
   public static void main(String[] args) {
      String data = "ABCDEFG";
      try (StringReader reader = new StringReader(data)) {
         char[] buffer = new char[10];
         // Fill initial buffer to show unused areas later
         for (int i = 0; i < buffer.length; i++) {
            buffer[i] = '-';
         }

         int charsRead = reader.read(buffer, 2, 5); // Start at index 2, read 5 characters
         System.out.println("Characters read: " + charsRead);
         System.out.println("Buffer content: " + new String(buffer));
      } 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: --ABCDE---

Explanation

• We read 5 characters starting at index 2 in the buffer.

• Unused positions (like index 0 and 1) remain as '-' to visualize where data was placed.

Example - Multiple reads with different offsets

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

ReaderDemo.java

package com.tutorialspoint;

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

public class ReaderDemo {
   public static void main(String[] args) {
      String data = "123456789";
      try (StringReader reader = new StringReader(data)) {
         char[] buffer = new char[10];

         int read1 = reader.read(buffer, 0, 4);  // Fill from index 0
         int read2 = reader.read(buffer, 5, 3);  // Fill from index 5

         System.out.println("First read (" + read1 + " chars): " + new String(buffer, 0, read1));
         System.out.println("Second read (" + read2 + " chars): " + new String(buffer, 5, read2));
         System.out.println("Full buffer: " + new String(buffer));
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

First read (4 chars): 1234
Second read (3 chars): 567
Full buffer: 1234567

Explanation

• First, we read 4 characters into the beginning of the buffer.

• Then, we read the next 3 characters into a different part of the buffer (index 5).