Java - Reader read(char[] cbuf) method

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Description

The Java Reader read(char[] cbuf) method reads characters into 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) method.

public int read(char[] cbuf)

Parameters

cbuf − Destination buffer.

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) method

The following example shows the usage of Reader read(char[] cbuf) 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 an array.
         System.out.println( reader.read(cbuf));

         // 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 - Read a string in chunks using StringReader

The following example shows the usage of Reader read(char[] cbuf) 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 = "Java IO Reader Example";
      try (StringReader reader = new StringReader(data)) {
         char[] buffer = new char[10];  // Read in chunks of 10 characters
         int charsRead;
         while ((charsRead = reader.read(buffer)) != -1) {
            System.out.println("Read " + charsRead + " chars: " + new String(buffer, 0, charsRead));
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Read 10 chars: Java IO Re
Read 10 chars: ader Examp
Read 3 chars: le

Explanation

• We use a buffer of size 10 and read repeatedly until the end of the string.

• read(char[]) fills the buffer and returns how many characters were read.

• We convert only the valid portion (0 to charsRead) of the buffer to a string.

Example - Use read(char[]) with a smaller buffer

The following example shows the usage of Reader read(char[] cbuf) 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 = "ABCD";
      try (StringReader reader = new StringReader(data)) {
         char[] buffer = new char[2];  // Small buffer
         int charsRead;
         while ((charsRead = reader.read(buffer)) != -1) {
            System.out.println("Read: " + new String(buffer, 0, charsRead));
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Read: AB 
Read: CD

Explanation

• The string "ABCD" is read in 2-character chunks.

• On each iteration, we print the part of the buffer that was filled.