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What is the ByteBuffer.asCharBuffer() method in Java?

Muhammad Ashir

Grokking Modern System Design Interview for Engineers & Managers

Ace your System Design Interview and take your career to the next level. Learn to handle the design of applications like Netflix, Quora, Facebook, Uber, and many more in a 45-min interview. Learn the RESHADED framework for architecting web-scale applications by determining requirements, constraints, and assumptions before diving into a step-by-step design process.

The java.nio.ByteBuffer class provides the asCharBuffer() method to create a char view-buffer of the underlying byte array of the original buffer.

A view-buffer is another buffer that is backed by the same array as the corresponding ByteBuffer object. Any changes made to the original ByteBuffer or the corresponding view-buffer are visible in both places. However, the position, limit, and mark of the two buffers are independent of each other.

Properties

  • The position of the new buffer is zero. It defines the byte index from which the next value will be read from the buffer.

  • The capacity and limit of the new buffer are given by the number of remaining bytes divided by two. The capacity is the index of the last byte in the buffer. The limit is the index of the first index that should not be read from the buffer.

  • The mark will be undefined. This marks the current index of the buffer so that we can return to it when the reset() method is called.

  • The new buffer will only be direct if this buffer is also direct.

  • The new buffer is only read-only if this buffer is also read-only.

Syntax

public abstract CharBuffer asCharBuffer()

Parameters

asCharBuffer() does not take any arguments.

Return value

asCharBuffer() returns a new CharBuffer view.

Code

import java.nio.*;
import java.util.*;
class main {
public static void main( String args[] ) {
ByteBuffer buffer = ByteBuffer.allocate(8);
CharBuffer charBuff = buffer.asCharBuffer();
charBuff.put('a');
charBuff.put('b');
charBuff.put('c');
charBuff.put('d');
charBuff.rewind();
System.out.print("using CharBuffer: ");
for(int i = buffer.position(); i < buffer.limit()/2; i++){
System.out.print(buffer.getChar() + " ");
}
System.out.print("\nusing ByteBuffer: ");
buffer.rewind();
buffer.put(5,(byte)'X');
for(int i = buffer.position(); i < buffer.limit()/2; i++){
System.out.print(buffer.getChar() + " ");
}
}
}

In the code above, we create a ByteBuffer called buffer and allocate it with a capacity of 88 bytes. Next, we create a view buffer using the asCharBuffer() method and call it charBuff. This allows us to put values of type char in the buffer.

We use the put() method of the CharBuffer object to write values into the buffer as follows:

charBuff.put()

The for loop in line 1515 prints the contents of the byte array using CharBuffer. In this loop, we start from the index given by position() all the way through the index at limit() / 2. We need to divide by 22 because the ByteBuffer is indexed by bytes and each char value takes two bytes of memory.

In line 2121, we put the character X in the buffer using the put() method of the ByteBuffer object instead of the CharBuffer object. However, the changes are also visible in the buffer object.

RELATED TAGS

java
communitycreator

Grokking Modern System Design Interview for Engineers & Managers

Ace your System Design Interview and take your career to the next level. Learn to handle the design of applications like Netflix, Quora, Facebook, Uber, and many more in a 45-min interview. Learn the RESHADED framework for architecting web-scale applications by determining requirements, constraints, and assumptions before diving into a step-by-step design process.

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