CharBuffer read() methods in Java with Examples

The read() method of java.nio.CharBuffer Class is used to read characters into the specified character buffer. The buffer is used as a repository of characters as-is: the only changes made are the results of a put operation. No flipping or rewinding of the buffer is performed.

Syntax:

public int read(CharBuffer target)

Parameter: This method takes the buffer to read characters into.

Return Value: This method returns the number of characters added to the buffer, or -1 if this source of characters is at its end.

Exception: This method throws following exception:-

• IOException – if an I/O error occurs
• NullPointerException – if target is null
• ReadOnlyBufferException – if target is a read only buffer

Below are the examples to illustrate the read() method:

Examples 1:

// Java program to demonstrate
// read() method

import java.nio.*;
import java.util.*;
import java.io.IOException;

public class GFG {
    public static void main(String[] args)
    {
        try {

            // Declare and initialize the char array
            char[] cb1 = { 'x', 'y', 'z' };
            char[] cb2 = { 'a', 'b', 'c', 'd', 'e' };

            // wrap the char array into CharBuffer
            // using wrap() method
            CharBuffer charBuffer1
                = CharBuffer.wrap(cb1);

            // wrap the char array into CharBuffer
            // using wrap() method
            CharBuffer charBuffer2
                = CharBuffer.wrap(cb2);

            // print the byte buffer
            System.out.println("CharBuffer Before operation is: "
                               + Arrays.toString(
                                     charBuffer1.array())
                               + "\nTarget Charbuffer: "
                               + Arrays.toString(
                                     charBuffer2.array()));

            // Get the value of the number of Character
            // read from the charBuffer
            // using read() method
            int value
                = charBuffer1
                      .read(charBuffer2);

            // print the byte buffer
            System.out.println("\nCharBuffer After operation is: "
                               + Arrays.toString(
                                     charBuffer1.array())
                               + "\nTarget Charbuffer: "
                               + Arrays.toString(
                                     charBuffer2.array())
                               + "\nno of value changed: "
                               + value);
        }
        catch (IOException e) {
            System.out.println("an I/O error occurs");
            System.out.println("Exception throws: " + e);
        }
        catch (NullPointerException e) {
            System.out.println("target charbuffer is null");
            System.out.println("Exception throws: " + e);
        }
        catch (ReadOnlyBufferException e) {
            System.out.println("target is a read only buffer");
            System.out.println("Exception throws: " + e);
        }
    }
}

Output:

CharBuffer Before operation is: [x, y, z]
Target Charbuffer: [a, b, c, d, e]

CharBuffer After operation is: [x, y, z]
Target Charbuffer: [x, y, z, d, e]
no of value changed: 3

Examples 2: For NullPointerException

// Java program to demonstrate
// read() method

import java.nio.*;
import java.util.*;
import java.io.IOException;

public class GFG {
    public static void main(String[] args)
    {
        try {

            // Declare and initialize the char array
            char[] cb1 = { 'x', 'y', 'z' };

            // wrap the char array into CharBuffer
            // using wrap() method
            CharBuffer charBuffer1
                = CharBuffer.wrap(cb1);

            // print the byte buffer
            System.out.println("CharBuffer Before operation is: "
                               + Arrays.toString(
                                     charBuffer1.array()));

            // Get the value of number of Character
            // read from the charBuffer
            // using read() method
            int value = charBuffer1.read(null);
        }

        catch (IOException e) {
            System.out.println("\nan I/O error occurs");
            System.out.println("Exception throws: " + e);
        }

        catch (NullPointerException e) {
            System.out.println("\ntarget charbuffer is null");
            System.out.println("Exception throws: " + e);
        }

        catch (ReadOnlyBufferException e) {
            System.out.println("\ntarget is a read only buffer");
            System.out.println("Exception throws: " + e);
        }
    }
}

Output:

CharBuffer Before operation is: [x, y, z]

target charbuffer is null
Exception throws: java.lang.NullPointerException

Examples 3: For ReadOnlyBufferException

// Java program to demonstrate
// read() method

import java.nio.*;
import java.util.*;
import java.io.IOException;

public class GFG {
    public static void main(String[] args)
    {
        try {

            // Declare and initialize the char array
            char[] cb1 = { 'x', 'y', 'z' };
            char[] cb2 = { 'a', 'b', 'c', 'd', 'e' };

            // wrap the char array into CharBuffer
            // using wrap() method
            CharBuffer charBuffer1
                = CharBuffer.wrap(cb1);

            // wrap the char array into CharBuffer
            // using wrap() method
            CharBuffer charBuffer2
                = CharBuffer.wrap(cb2);

            // print the byte buffer
            System.out.println("CharBuffer Before operation is: "
                               + Arrays.toString(
                                     charBuffer1.array())
                               + "\nTarget Charbuffer: "
                               + Arrays.toString(
                                     charBuffer2.array()));

            // converting Charbuffer to readonlybuff
            CharBuffer readonlybuff
                = charBuffer2.asReadOnlyBuffer();

            // Get the value of number of Character
            // read from the charBuffer
            // using read() method
            int value = charBuffer1.read(readonlybuff);

            // print the byte buffer
            System.out.println("\nCharBuffer After operation is: "
                               + Arrays.toString(
                                     charBuffer1.array())
                               + "\nTarget Charbuffer: "
                               + Arrays.toString(
                                     charBuffer2.array())
                               + "\nno of value changed: "
                               + value);
        }
        catch (IOException e) {
            System.out.println("\nan I/O error occurs");
            System.out.println("Exception throws: " + e);
        }
        catch (NullPointerException e) {
            System.out.println("\ntarget charbuffer is null");
            System.out.println("Exception throws: " + e);
        }
        catch (ReadOnlyBufferException e) {
            System.out.println("\ntarget is a read only buffer");
            System.out.println("Exception throws: " + e);
        }
    }
}

Output:

CharBuffer Before operation is: [x, y, z]
Target Charbuffer: [a, b, c, d, e]

target is a read only buffer
Exception throws: java.nio.ReadOnlyBufferException

Reference: https://docs.oracle.com/javase/9/docs/api/java/nio/CharBuffer.html#read-java.nio.CharBuffer-