Java : Buffer with Examples

Buffer (Java SE 20 & JDK 20) API Examples.
You will find code examples on most Buffer methods.

Summary

A container for data of a specific primitive type.

Class diagram

final var buffer = IntBuffer.allocate(5);

System.out.println(buffer instanceof Buffer); // true

System.out.println(buffer.capacity()); // 5
System.out.println(buffer.limit()); // 5
System.out.println(buffer.position()); // 0

buffer.put(10);
System.out.println(buffer.position()); // 1

buffer.put(20);
System.out.println(buffer.position()); // 2

buffer.put(30);
System.out.println(buffer.position()); // 3

if (buffer.hasArray()) {
    final var ret = buffer.array();
    System.out.println(Arrays.toString(ret)); // [10, 20, 30, 0, 0]
}

final byte[] array = {10, 20, 30};
final var buffer = ByteBuffer.wrap(array);

System.out.println(buffer instanceof Buffer); // true

System.out.println(buffer.capacity()); // 3
System.out.println(buffer.limit()); // 3
System.out.println(buffer.position()); // 0

System.out.println(buffer.get()); // 10
System.out.println(buffer.position()); // 1

System.out.println(buffer.get()); // 20
System.out.println(buffer.position()); // 2

System.out.println(buffer.get()); // 30
System.out.println(buffer.position()); // 3

Methods

abstract Object array ()

Returns the array that backs this buffer (optional operation).

final Buffer buffer = IntBuffer.allocate(5)
        .put(10)
        .put(20)
        .put(30);

if (buffer.hasArray()) {
    if (buffer.array() instanceof int[] array) {
        System.out.println(Arrays.toString(array)); // [10, 20, 30, 0, 0]
    }
}

abstract int arrayOffset ()

Returns the offset within this buffer's backing array of the first element of the buffer (optional operation).

final byte[] bytes = {10, 20, 30, 40, 50};

final var buffer = ByteBuffer.wrap(bytes);
System.out.println(buffer instanceof Buffer); // true

final var sliced = buffer.slice(2, 3);
System.out.println(sliced instanceof Buffer); // true

System.out.println(buffer); // java.nio.HeapByteBuffer[pos=0 lim=5 cap=5]
if (buffer.hasArray()) {
    System.out.println(buffer.arrayOffset()); // 0
    System.out.println(buffer.get()); // 10
    System.out.println(buffer.get()); // 20
    System.out.println(buffer.get()); // 30
    System.out.println(buffer.get()); // 40
    System.out.println(buffer.get()); // 50
}

System.out.println(sliced); // java.nio.HeapByteBuffer[pos=0 lim=3 cap=3]
if (sliced.hasArray()) {
    System.out.println(sliced.arrayOffset()); // 2
    System.out.println(sliced.get()); // 30
    System.out.println(sliced.get()); // 40
    System.out.println(sliced.get()); // 50
}

final int capacity ()

Returns this buffer's capacity.

final Buffer buffer = ByteBuffer.allocate(100);
System.out.println(buffer.capacity()); // 100

final byte[] bytes = {10, 20, 30, 40, 50};
final Buffer buffer = ByteBuffer.wrap(bytes);

System.out.println(buffer.capacity()); // 5

Buffer clear ()

Clears this buffer.

Please see also : rewind()

final byte[] array = {10, 20, 30, 40, 50};
final var buffer = ByteBuffer.wrap(array);
System.out.println(buffer instanceof Buffer); // true

buffer.position(2);
buffer.limit(4);

System.out.println(buffer); // java.nio.HeapByteBuffer[pos=2 lim=4 cap=5]

System.out.println(buffer.get()); // 30
System.out.println(buffer.get()); // 40
System.out.println(buffer.hasRemaining()); // false

System.out.println(buffer.clear()); // java.nio.HeapByteBuffer[pos=0 lim=5 cap=5]

System.out.println(buffer.get()); // 10
System.out.println(buffer.get()); // 20
System.out.println(buffer.get()); // 30
System.out.println(buffer.get()); // 40
System.out.println(buffer.get()); // 50
System.out.println(buffer.hasRemaining()); // false

abstract Buffer duplicate ()

Creates a new buffer that shares this buffer's content.

final byte[] array = {10, 20, 30, 40, 50};
final var buffer = ByteBuffer.wrap(array);
System.out.println(buffer instanceof Buffer); // true

buffer.position(1);
buffer.limit(4);

final var duplicated = buffer.duplicate();
System.out.println(duplicated instanceof Buffer); // true

System.out.println(buffer); // java.nio.HeapByteBuffer[pos=1 lim=4 cap=5]
System.out.println(duplicated); // java.nio.HeapByteBuffer[pos=1 lim=4 cap=5]

System.out.println(buffer.get()); // 20
System.out.println(buffer.get()); // 30
System.out.println(buffer.get()); // 40

System.out.println(duplicated.get()); // 20
System.out.println(duplicated.get()); // 30
System.out.println(duplicated.get()); // 40

Buffer flip ()

Flips this buffer.

final byte[] array = {10, 20, 30, 40, 50};
final var buffer = ByteBuffer.wrap(array);
System.out.println(buffer instanceof Buffer); // true

System.out.println(buffer.get()); // 10
System.out.println(buffer.get()); // 20
System.out.println(buffer.get()); // 30

System.out.println(buffer); // java.nio.HeapByteBuffer[pos=3 lim=5 cap=5]
System.out.println(buffer.flip()); // java.nio.HeapByteBuffer[pos=0 lim=3 cap=5]

System.out.println(buffer.get()); // 10
System.out.println(buffer.get()); // 20
System.out.println(buffer.get()); // 30

abstract boolean hasArray ()

Tells whether or not this buffer is backed by an accessible array.

final var buffer = IntBuffer.allocate(5)
        .put(10)
        .put(20)
        .put(30);
System.out.println(buffer instanceof Buffer); // true

final var ret = buffer.hasArray();
System.out.println(ret); // true

if (ret) {
    final var array = buffer.array();
    System.out.println(Arrays.toString(array)); // [10, 20, 30, 0, 0]
}

final var buffer = ByteBuffer.allocateDirect(5);
System.out.println(buffer instanceof Buffer); // true

System.out.println(buffer.hasArray()); // false
try {
    final var array = buffer.array();
} catch (UnsupportedOperationException e) {
    System.out.println("UnsupportedOperationException!");
}

// Result
// ↓
//UnsupportedOperationException!

final boolean hasRemaining ()

Tells whether there are any elements between the current position and the limit.

final byte[] array = {10, 20, 30, 40};
final var buffer = ByteBuffer.wrap(array);
System.out.println(buffer instanceof Buffer); // true

buffer.limit(3);

System.out.println(buffer); // java.nio.HeapByteBuffer[pos=0 lim=3 cap=4]
System.out.println(buffer.hasRemaining()); // true
System.out.println(buffer.remaining()); // 3

System.out.println(buffer.get()); // 10

System.out.println(buffer); // java.nio.HeapByteBuffer[pos=1 lim=3 cap=4]
System.out.println(buffer.hasRemaining()); // true
System.out.println(buffer.remaining()); // 2

System.out.println(buffer.get()); // 20

System.out.println(buffer); // java.nio.HeapByteBuffer[pos=2 lim=3 cap=4]
System.out.println(buffer.hasRemaining()); // true
System.out.println(buffer.remaining()); // 1

System.out.println(buffer.get()); // 30

System.out.println(buffer); // java.nio.HeapByteBuffer[pos=3 lim=3 cap=4]
System.out.println(buffer.hasRemaining()); // false
System.out.println(buffer.remaining()); // 0

abstract boolean isDirect ()

Tells whether or not this buffer is direct.

final Buffer buffer = ByteBuffer.allocate(5);
System.out.println(buffer.isDirect()); // false

final Buffer buffer = ByteBuffer.allocateDirect(5);
System.out.println(buffer.isDirect()); // true

abstract boolean isReadOnly ()

Tells whether or not this buffer is read-only.

final var buffer = IntBuffer.allocate(5);
System.out.println(buffer instanceof Buffer); // true

System.out.println(buffer.isReadOnly()); // false

buffer.put(10);
buffer.put(20);
buffer.put(30);

System.out.println(buffer); // java.nio.HeapIntBuffer[pos=3 lim=5 cap=5]

final var buffer = IntBuffer.allocate(5).asReadOnlyBuffer();
System.out.println(buffer instanceof Buffer); // true

System.out.println(buffer.isReadOnly()); // true

try {
    buffer.put(10);
} catch (ReadOnlyBufferException e) {
    System.out.println("ReadOnlyBufferException!");
}

// Result
// ↓
//ReadOnlyBufferException!

final int limit ()

Returns this buffer's limit.

final byte[] array = {10, 20, 30, 40, 50};
final Buffer buffer = ByteBuffer.wrap(array);

System.out.println(buffer); // java.nio.HeapByteBuffer[pos=0 lim=5 cap=5]
System.out.println(buffer.limit()); // 5

System.out.println(buffer.limit(3)); // java.nio.HeapByteBuffer[pos=0 lim=3 cap=5]
System.out.println(buffer.limit()); // 3

System.out.println(buffer.clear()); // java.nio.HeapByteBuffer[pos=0 lim=5 cap=5]
System.out.println(buffer.limit()); // 5

final byte[] array = {10, 20, 30, 40, 50};
final var buffer = ByteBuffer.wrap(array);
System.out.println(buffer instanceof Buffer); // true

System.out.println(buffer.limit(3)); // java.nio.HeapByteBuffer[pos=0 lim=3 cap=5]

System.out.println(buffer.get()); // 10
System.out.println(buffer.get()); // 20
System.out.println(buffer.get()); // 30

try {
    final var ret = buffer.get();
} catch (BufferUnderflowException e) {
    System.out.println("BufferUnderflowException!");
}

// Result
// ↓
//BufferUnderflowException!

Buffer limit (int newLimit)

Sets this buffer's limit.

Please see limit().

Buffer mark ()

Sets this buffer's mark at its position.

final byte[] array = {10, 20, 30, 40, 50};
final var buffer = ByteBuffer.wrap(array);
System.out.println(buffer instanceof Buffer); // true

System.out.println(buffer.get()); // 10
System.out.println(buffer.get()); // 20

System.out.println(buffer.position()); // 2
System.out.println(buffer.mark()); // java.nio.HeapByteBuffer[pos=2 lim=5 cap=5]

System.out.println(buffer.get()); // 30
System.out.println(buffer.get()); // 40
System.out.println(buffer.get()); // 50

System.out.println(buffer.position()); // 5
System.out.println(buffer.reset()); // java.nio.HeapByteBuffer[pos=2 lim=5 cap=5]

System.out.println(buffer.get()); // 30
System.out.println(buffer.get()); // 40
System.out.println(buffer.get()); // 50

final int position ()

Returns this buffer's position.

final byte[] array = {10, 20, 30, 40, 50};
final var buffer = ByteBuffer.wrap(array);
System.out.println(buffer instanceof Buffer); // true

System.out.println(buffer.position()); // 0

System.out.println(buffer.get()); // 10
System.out.println(buffer.position()); // 1

System.out.println(buffer.get()); // 20
System.out.println(buffer.position()); // 2

System.out.println(buffer.get()); // 30
System.out.println(buffer.position()); // 3

System.out.println(buffer.get()); // 40
System.out.println(buffer.position()); // 4

System.out.println(buffer.get()); // 50
System.out.println(buffer.position()); // 5

System.out.println(buffer.position(3)); // java.nio.HeapByteBuffer[pos=3 lim=5 cap=5]

System.out.println(buffer.get()); // 40
System.out.println(buffer.position()); // 4

System.out.println(buffer.get()); // 50
System.out.println(buffer.position()); // 5

Buffer position (int newPosition)

Sets this buffer's position.

Please see position().

final int remaining ()

Returns the number of elements between the current position and the limit.

Please see hasRemaining().

Buffer reset ()

Resets this buffer's position to the previously-marked position.

Please see mark().

Buffer rewind ()

Rewinds this buffer.

Please see also : clear()

final int[] array = {10, 20, 30, 40, 50};
final Buffer buffer = IntBuffer.wrap(array);

buffer.position(2);
buffer.limit(4);

System.out.println(buffer.position()); // 2
System.out.println(buffer.limit()); // 4

System.out.println(buffer.rewind()); // java.nio.HeapIntBuffer[pos=0 lim=4 cap=5]

System.out.println(buffer.position()); // 0
System.out.println(buffer.limit()); // 4

abstract Buffer slice ()

Creates a new buffer whose content is a shared subsequence of this buffer's content.

final byte[] array = {10, 20, 30, 40, 50};
final var buffer = ByteBuffer.wrap(array);
System.out.println(buffer instanceof Buffer); // true

buffer.position(1);
buffer.limit(4);

final var sliced = buffer.slice();
System.out.println(sliced instanceof Buffer); // true

System.out.println(buffer); // java.nio.HeapByteBuffer[pos=1 lim=4 cap=5]
System.out.println(sliced); // java.nio.HeapByteBuffer[pos=0 lim=3 cap=3]

System.out.println(buffer.get()); // 20
System.out.println(buffer.get()); // 30
System.out.println(buffer.get()); // 40
System.out.println(buffer.hasRemaining()); // false

System.out.println(sliced.get()); // 20
System.out.println(sliced.get()); // 30
System.out.println(sliced.get()); // 40
System.out.println(sliced.hasRemaining()); // false

abstract Buffer slice (int index, int length)