Buffer
- Java course
- Expert
- Lesson 13/46
- 5 min
Learn the NIO buffer with Buffer.
The Buffer concept
In NIO data is carried inside a Buffer. A buffer is like an array of primitives; it adds state such as position, limit, and capacity. This state lets a single structure manage both reading and writing.
Example: ByteBuffer b = ByteBuffer.allocate(4) allocates a four-byte buffer. b.put((byte) 5) writes one byte; b.flip() switches from write mode to read mode; b.get() reads the next byte. This flow is the basis of block-wise data processing.
allocate and wrap
There are two common ways to create a buffer. ByteBuffer.allocate(n) allocates an empty buffer; you write data into it with put. ByteBuffer.wrap(array) wraps an existing byte array so it can be read directly.
Example: ByteBuffer.wrap(new byte[]{65, 66}) turns the ready array into a buffer; get() returns 65 first, then 66. allocate requests new memory; wrap reuses what exists. Both expose the same ByteBuffer API.
Practice Write and read with ByteBuffer
Create a buffer with ByteBuffer.allocate(4). Write (byte) 10 and (byte) 20 with put. Switch to read mode with flip. Get the first byte with get and print it with System.out.println.
Starter code
// Create a buffer with ByteBuffer
// Write two bytes with put
// Print the first byte after flipSample solution
import java.nio.ByteBuffer;
public class BufferDemo {
public static void main(String[] args) {
ByteBuffer b = ByteBuffer.allocate(4);
b.put((byte) 10);
b.put((byte) 20);
b.flip();
System.out.println(b.get());
}
}Expected output
10
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which method switches a ByteBuffer from write mode to read mode?
- allocate
- flip Correct answer
- put
- get
Explanation: flip switches from write mode to read mode.
2 Complete the flip call
b.____();b.flip();Explanation: flip switches to read mode.
3 Match the Buffer methods
| Term | Meaning |
|---|---|
allocate |
Allocates a buffer |
put |
Writes data |
flip |
Switches mode |
get |
Reads data |