Java - InputStreamReader read(char[] cbuf, int offset, int length) method

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Description

The Java InputStreamReader read(char[] cbuf, int offset, int length) method reads multiple characters into a character array (cbuf), starting from a given offset (off) and reading up to len characters. Returns the actual number of characters read (-1 if EOF is reached).

Declaration

Following is the declaration for java.io.InputStreamReader.read(char[] cbuf, int offset, int length) method −

public int read(char[] cbuf, int offset, int length)

Parameters

• cbuf − Destination character buffer.

• offset − Offset at which to start storing characters.

• length − Maximum numbers of characters to read.

Return Value

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

Exception

IOException − If an I/O error occurs.

Example - Usage of InputStreamReader read(char[] cbuf, int offset, int length) method

The following example shows the usage of Java InputStreamReader read(char[] cbuf, int offset, int length) method.

InputStreamReaderDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;

public class InputStreamReaderDemo {

   public static void main(String[] args) throws IOException {
      InputStreamReader isr = null;
      FileInputStream fis = null;
      char[] cbuf = new char[5];
      int i;
      
      try {
         // new input stream reader is created 
         fis = new FileInputStream("test.txt");
         isr = new InputStreamReader(fis);
         
         // reads into the char buffer
         i = isr.read(cbuf, 2, 3);
         
         // prints the number of characters
         System.out.println("Number of characters read: "+i);
         
         // for each character in the character buffer
         for(char c:cbuf) {
         
            // for empty character
            if(((int)c) == 0)
               c = '-';
            
            // prints the characters
            System.out.println(c);
         }
         
      } catch (Exception e) {
         // print error
         e.printStackTrace();
      } finally {
         // closes the stream and releases resources associated
         if(fis!=null)
            fis.close();
         if(isr!=null)
            isr.close();
      }   
   }
}

Output(Assuming test.txt contains "ABCDE")

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

Number of characters read: 3
-
-
A
B
C

Example - Reading a Portion of a File Using InputStreamReader

The following example shows the usage of Java InputStreamReader read(char[] cbuf, int offset, int length) method.

InputStreamReaderDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;

public class InputStreamReaderDemo {
   public static void main(String[] args) {
      try (InputStreamReader reader = new InputStreamReader(new FileInputStream("example.txt"))) {
         char[] buffer = new char[10]; // Character buffer of size 10
         int charsRead = reader.read(buffer, 2, 5); // Read 5 characters, store from index 2

         if (charsRead != -1) {
            System.out.println("Characters read: " + charsRead);
            System.out.println("Buffer content: " + new String(buffer)); // Print full buffer
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output(if example.txt contains "HelloWorld")

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

Characters read: 5
Buffer content:   Hello

Explanation

• Uses InputStreamReader to read from "example.txt".

• Creates a character buffer (char[]) of size 10.

• Reads 5 characters into buffer, starting at index 2.

• Prints the full buffer, showing that the first two positions are empty.

Example - Reading a File in Chunks Using BufferedReader

The following example shows the usage of Java InputStreamReader read(char[] cbuf, int offset, int length) method.

InputStreamReaderDemo.java

package com.tutorialspoint;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;

public class InputStreamReaderDemo {
   public static void main(String[] args) {
      try (InputStreamReader reader = new InputStreamReader(new FileInputStream("example.txt"));
         BufferedReader bufferedReader = new BufferedReader(reader)) {

         char[] buffer = new char[10]; // Buffer of size 10
         int charsRead;

         while ((charsRead = bufferedReader.read(buffer, 3, 4)) != -1) { // Read 4 characters at index 3
            System.out.println("Characters read: " + charsRead);
            System.out.println("Buffer content: " + new String(buffer)); // Print full buffer
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output(if example.txt contains "Microservices")

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

Characters read: 4
Buffer content:    Micr
Characters read: 4
Buffer content:    ices

Explanation

• Uses BufferedReader for efficient reading.

• Reads 4 characters at a time into buffer, starting at index 3.

• Prints the buffer contents after each read operation.