CharBuffer read() methods in Java with Examples

Last Updated : 28 Jul, 2019

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-