java.nio · java.base · since Java 1.4

ByteBuffer

declaration

public abstract class ByteBuffer extends Buffer
        implements Comparable<ByteBuffer>

The NIO byte container with the position/limit/capacity state machine: fill → flip() → drain → clear. Heap or direct; typed getters/putters with configurable byte order.

Key methods

`static ByteBuffer allocate(int) / allocateDirect(int)`	Heap vs off-heap (direct: no copy for I/O, pricier to create).
`Buffer flip()`	Switch from writing to reading — the forgotten call behind half of NIO bugs.
`Buffer clear() / compact()`	Reset for refilling (clear discards; compact keeps unread bytes).
`int getInt() / putInt(int)`	Typed access at the position (all primitives).
`ByteBuffer order(ByteOrder bo)`	Endianness — default BIG_ENDIAN; most native formats are little.