java nio 的重点Buffer，为了更深入了解其原理，看了下它的源码，在源码实现上还是很简单的，
ByteBuffer的子类HeapByteBuffer实现了它的各种操作，底层是通过byte数组对数据进行保存的。
/**
* A byte buffer.
*
* <p> This class defines six categories of operations upon
* byte buffers:
*
* <ul>
*
* <li><p> Absolute and relative {@link #get() <i>get</i>} and
* {@link #put(byte) <i>put</i>} methods that read and write
* single bytes; </p></li>
*
* <li><p> Relative {@link #get(byte[]) <i>bulk get</i>}
* methods that transfer contiguous sequences of bytes from this buffer
* into an array; </p></li>
*
* <li><p> Relative {@link #put(byte[]) <i>bulk put</i>}
* methods that transfer contiguous sequences of bytes from a
* byte array or some other byte
* buffer into this buffer; </p></li>
*
*
*
* <li><p> Absolute and relative {@link #getChar() <i>get</i>}
* and {@link #putChar(char) <i>put</i>} methods that read and
* write values of other primitive types, translating them to and from
* sequences of bytes in a particular byte order; </p></li>
*
* <li><p> Methods for creating <i><a href="#views">view buffers</a></i>,
* which allow a byte buffer to be viewed as a buffer containing values of
* some other primitive type; and </p></li>
*
*
*
* <li><p> Methods for {@link #compact compacting}, {@link
* #duplicate duplicating}, and {@link #slice slicing}
* a byte buffer. </p></li>
*
* </ul>
*
* <p> Byte buffers can be created either by {@link #allocate
* <i>allocation</i>}, which allocates space for the buffer's
* <p>
* <p>
* <p>
* content, or by {@link #wrap(byte[]) <i>wrapping</i>} an
* existing byte array into a buffer.
*
*
* <a name="direct"></a>
* <h2> Direct <i>vs.</i> non-direct buffers </h2>
*
* <p> A byte buffer is either <i>direct</i> or <i>non-direct</i>. Given a
* direct byte buffer, the Java virtual machine will make a best effort to
* perform native I/O operations directly upon it. That is, it will attempt to
* avoid copying the buffer's content to (or from) an intermediate buffer
* before (or after) each invocation of one of the underlying operating
* system's native I/O operations.
*
* <p> A direct byte buffer may be created by invoking the {@link
* #allocateDirect(int) allocateDirect} factory method of this class. The
* buffers returned by this method typically have somewhat higher allocation
* and deallocation costs than non-direct buffers. The contents of direct
* buffers may reside outside of the normal garbage-collected heap, and so
* their impact upon the memory footprint of an application might not be
* obvious. It is therefore recommended that direct buffers be allocated
* primarily for large, long-lived buffers that are subject to the underlying
* system's native I/O operations. In general it is best to allocate direct
* buffers only when they yield a measureable gain in program performance.
*
* <p> A direct byte buffer may also be created by {@link
* java.nio.channels.FileChannel#map mapping} a region of a file
* directly into memory. An implementation of the Java platform may optionally
* support the creation of direct byte buffers from native code via JNI. If an
* instance of one of these kinds of buffers refers to an inaccessible region
* of memory then an attempt to access that region will not change the buffer's
* content and will cause an unspecified exception to be thrown either at the
* time of the access or at some later time.
*
* <p> Whether a byte buffer is direct or non-direct may be determined by
* invoking its {@link #isDirect isDirect} method. This method is provided so
* that explicit buffer management can be done in performance-critical code.
*
*
* <a name="bin"></a>
* <h2> Access to binary data </h2>
*
* <p> This class defines methods for reading and writing values of all other
* primitive types, except <tt>boolean</tt>. Primitive values are translated
* to (or from) sequences of bytes according to the buffer's current byte
* order, which may be retrieved and modified via the {@link #order order}
* methods. Specific byte orders are represented by instances of the {@link
* ByteOrder} class. The initial order of a byte buffer is always {@link
* ByteOrder#BIG_ENDIAN BIG_ENDIAN}.
*
* <p> For access to heterogeneous binary data, that is, sequences of values of
* different types, this class defines a family of absolute and relative
* <i>get</i> and <i>put</i> methods for each type. For 32-bit floating-point
* values, for example, this class defines:
*
* <blockquote><pre>
* float {@link #getFloat()}
* float {@link #getFloat(int) getFloat(int index)}
* void {@link #putFloat(float) putFloat(float f)}
* void {@link #putFloat(int, float) putFloat(int index, float f)}</pre></blockquote>
*
* <p> Corresponding methods are defined for the types <tt>char</tt>,
* <tt>short</tt>, <tt>int</tt>, <tt>long</tt>, and <tt>double</tt>. The index
* parameters of the absolute <i>get</i> and <i>put</i> methods are in terms of
* bytes rather than of the type being read or written.
*
* <a name="views"></a>
*
* <p> For access to homogeneous binary data, that is, sequences of values of
* the same type, this class defines methods that can create <i>views</i> of a
* given byte buffer. A <i>view buffer</i> is simply another buffer whose
* content is backed by the byte buffer. Changes to the byte buffer's content
* will be visible in the view buffer, and vice versa; the two buffers'
* position, limit, and mark values are independent. The {@link
* #asFloatBuffer() asFloatBuffer} method, for example, creates an instance of
* the {@link FloatBuffer} class that is backed by the byte buffer upon which
* the method is invoked. Corresponding view-creation methods are defined for
* the types <tt>char</tt>, <tt>short</tt>, <tt>int</tt>, <tt>long</tt>, and
* <tt>double</tt>.
*
* <p> View buffers have three important advantages over the families of
* type-specific <i>get</i> and <i>put</i> methods described above:
*
* <ul>
*
* <li><p> A view buffer is indexed not in terms of bytes but rather in terms
* of the type-specific size of its values; </p></li>
*
* <li><p> A view buffer provides relative bulk <i>get</i> and <i>put</i>
* methods that can transfer contiguous sequences of values between a buffer
* and an array or some other buffer of the same type; and </p></li>
*
* <li><p> A view buffer is potentially much more efficient because it will
* be direct if, and only if, its backing byte buffer is direct. </p></li>
*
* </ul>
*
* <p> The byte order of a view buffer is fixed to be that of its byte buffer
* at the time that the view is created. </p>
*
*
* <h2> Invocation chaining </h2>
*
*
* <p> Methods in this class that do not otherwise have a value to return are
* specified to return the buffer upon which they are invoked. This allows
* method invocations to be chained.
* <p>
* <p>
* <p>
* The sequence of statements
*
* <blockquote><pre>
* bb.putInt(0xCAFEBABE);
* bb.putShort(3);
* bb.putShort(45);</pre></blockquote>
* <p>
* can, for example, be replaced by the single statement
*
* <blockquote><pre>
* bb.putInt(0xCAFEBABE).putShort(3).putShort(45);</pre></blockquote>
*
* @author Mark Reinhold
* @author JSR-51 Expert Group
* @since 1.4
*/
public abstract class ByteBuffer
extends Buffer
implements Comparable<ByteBuffer> {
//这些字段在此声明，而不是在Heap-X-Buffer中声明
//减少访问这些调用所需的虚拟方法调用次数
//值，编码小缓冲区时成本特别高.
/**
* 通过源码我们可以清楚的知道ByteBuffer底层其实就是一个比byte数组
*/
final byte[] hb; // 仅对堆缓冲区为非null
final int offset;
boolean isReadOnly; //仅对堆缓冲区有效
//创建一个具有给定标记，位置，限制，容量的新缓冲区
//后备数组和数组偏移量
//
ByteBuffer(int mark, int pos, int lim, int cap,
byte[] hb, int offset) {
/**
* 这里调用了java.nio.Buffer四个参数的构造方法，说明
* private int mark = -1;
* private int position = 0;
* private int limit;
* private int capacity;
* 都是父类的属性
*/
super(mark, pos, lim, cap);
this.hb = hb;
this.offset = offset;
}
// 使用给定的标记，位置，限制和容量创建新缓冲区
ByteBuffer(int mark, int pos, int lim, int cap) {
this(mark, pos, lim, cap, null, 0);
}
/**
* 分配新的直接字节缓冲区。
* <p>
* 新缓冲区的位置将为零，其限制将为其
* 容量，其标记将是未定义的，其每个元素都将是
* 初始化为零。是否有
* {@link #hasArray支持数组}未指定。
*
* @param capacity 新缓冲区的容量，以字节为单位
* @return 新的字节缓冲区
* @throws IllegalArgumentException 如果capacity 是负整数
* <p>
* 这里要注意的是直接缓冲区的意义，这个方法申请的空间不是在JVM堆中，
* 而是在JVM堆外操作系统的内存中获取空间，
* 省去了拷贝的开销
*/
public static ByteBuffer allocateDirect(int capacity) {
return new DirectByteBuffer(capacity);
}
/**
* 分配一个新的字节缓冲区。
* <p>
* 新缓冲区的位置将为零，其限制将为其
* 容量，其标记将是未定义的，其每个元素都将是
* 初始化为零。它将有一个{@link #array支持数组}，
* 及其{@link #arrayOffset数组偏移}将为零。
*
* @param capacity 新缓冲区的容量，以字节为单位
* @return 新的字节缓冲区
* @throws IllegalArgumentException 如果容量是负整数
*/
public static ByteBuffer allocate(int capacity) {
if (capacity < 0)
throw new IllegalArgumentException();
/**
* 在JVM堆中获取空间
* java.nio.HeapByteBuffer
*/
return new HeapByteBuffer(capacity, capacity);
}
/**
* 将字节数组包装到缓冲区中。
* <p>
* 新缓冲区将由给定的字节数组支持;
* 也就是说，对缓冲区的修改将导致数组被修改
* 反之亦然。新缓冲区的容量将是
* array.length ，其位置将offset，其限制
* 将是offset + length ，其标记将是未定义的。它的
* {@link #array backing array}将是给定的数组，和
* 它的{@link #arrayOffset数组偏移}将为零。
*
* @param array 将支持新缓冲区的数组
* @param offset 要使用的子阵列的偏移量;必须是非负的
* 不大于array.length 。新缓冲区的位置
* 将被设置为此值。
* @param length 要使用的子阵列的长度;
* 必须是非负的且不大于
* array.length - offset
* 新缓冲区的限制将设置为offset + length 。
* @return 新的字节缓冲区
* @throws IndexOutOfBoundsException 如果偏移和长度的先决条件
* 参数不成立
*/
public static ByteBuffer wrap(byte[] array,
int offset, int length) {
try {
return new HeapByteBuffer(array, offset, length);
} catch (IllegalArgumentException x) {
throw new IndexOutOfBoundsException();
}
}
/**
* 将字节数组包装到缓冲区中。
*/
public static ByteBuffer wrap(byte[] array) {
return wrap(array, 0, array.length);
}
/**
* 创建一个新的字节缓冲区，其内容是共享的子序列
* 此缓冲区的内容。
* <p>
* 新缓冲区的内容将从此缓冲区的当前开始
* 位置。此缓冲区内容的更改将在新的中显示
* 缓冲区，反之亦然;两个缓冲区的位置，限制和标记
* 值将是独立的。
* <p>
* 新缓冲区的位置将为零，其容量和限制
* 将是此缓冲区中剩余的字节数及其标记
* 将是未定义的。当且仅当这个时，新缓冲区将是直接的
* 缓冲区是直接的，只有当这个缓冲区时它才是只读的
* 是只读的。
*
* @return The new byte buffer
* <p>
* ByteBuffer的子类HeapByteBuffer对该方法的实现
* public ByteBuffer slice() {
* return new HeapByteBuffer(hb,-1,0,this.remaining(),this.remaining(),this.position() + offset);
* }
*/
public abstract ByteBuffer slice();
/**
* 创建一个共享此缓冲区内容的新字节缓冲区。
* <p>
* 新缓冲区的内容将是此缓冲区的内容。变化
* 此缓冲区的内容将在新缓冲区中显示，反之亦然;
* 两个缓冲区的位置，限制和标记值将是
* 独立。
* <p>
* 新缓冲区的容量，限制，位置和标记值将是
* 与此缓冲区的相同。如果，新的缓冲区将是直接的，
* 且仅当此缓冲区是直接的时，如果和，它将是只读的
* 仅当此缓冲区为只读时。
* <p>
* ByteBuffer的子类HeapByteBuffer对该方法的实现
* public ByteBuffer duplicate() {
* return new HeapByteBuffer(hb,this.markValue(),this.position(),this.limit(),this.capacity(),offset);
* }
* <p>
* HeapByteBuffer(byte[] buf,int mark, int pos, int lim, int cap,int off)
*/
public abstract ByteBuffer duplicate();
/**
* 创建一个共享此缓冲区的新的只读字节缓冲区
* 内容。
* <p>
* ByteBuffer的子类HeapByteBuffer对该方法的实现
* <p>
* public ByteBuffer asReadOnlyBuffer() {
* return new HeapByteBufferR(hb,this.markValue(),this.position(),this.limit(),this.capacity(),offset);
* }
* <p>
* HeapByteBufferR 是HeapByteBuffer的子类，内部将HeapByteBuffer的this.isReadOnly 属性设置为 true;
*/
public abstract ByteBuffer asReadOnlyBuffer();
// -- Singleton get / put方法 --
/**
* 相对 get 方法。读取此缓冲区的字节
* 当前位置，然后增加位置。
*
* @return 缓冲区当前位置的字节
* @throws BufferUnderflowException 如果缓冲区的当前位置不大于其限制抛出该异常
* <p>
* 在HeapByteBuffer中对该方法的实现
* public byte get() {
* return hb[ix(nextGetIndex())];
* }
* final int nextGetIndex() {
* if (position >= limit)
* throw new BufferUnderflowException();
* return position++;
* }
*/
public abstract byte get();
/**
* Relative <i>put</i> method <i>(optional operation)</i>.
*
* <p> Writes the given byte into this buffer at the current
* position, and then increments the position. </p>
*
* @param b The byte to be written
* @return This buffer
* @throws BufferOverflowException If this buffer's current position is not smaller than its limit
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer put(byte b);
/**
* Absolute <i>get</i> method. Reads the byte at the given
* index.
*
* @param index The index from which the byte will be read
* @return The byte at the given index
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit
*/
public abstract byte get(int index);
/**
* Absolute <i>put</i> method <i>(optional operation)</i>.
*
* <p> Writes the given byte into this buffer at the given
* index. </p>
*
* @param index The index at which the byte will be written
* @param b The byte value to be written
* @return This buffer
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer put(int index, byte b);
// -- Bulk get operations --
/**
* Relative bulk <i>get</i> method.
*
* <p> This method transfers bytes from this buffer into the given
* destination array. If there are fewer bytes remaining in the
* buffer than are required to satisfy the request, that is, if
* <tt>length</tt> <tt>></tt> <tt>remaining()</tt>, then no
* bytes are transferred and a {@link BufferUnderflowException} is
* thrown.
*
* <p> Otherwise, this method copies <tt>length</tt> bytes from this
* buffer into the given array, starting at the current position of this
* buffer and at the given offset in the array. The position of this
* buffer is then incremented by <tt>length</tt>.
*
* <p> In other words, an invocation of this method of the form
* <tt>src.get(dst, off, len)</tt> has exactly the same effect as
* the loop
*
* <pre>{@code
* for (int i = off; i < off + len; i++)
* dst[i] = src.get():
* }</pre>
* <p>
* except that it first checks that there are sufficient bytes in
* this buffer and it is potentially much more efficient.
*
* @param dst The array into which bytes are to be written
* @param offset The offset within the array of the first byte to be
* written; must be non-negative and no larger than
* <tt>dst.length</tt>
* @param length The maximum number of bytes to be written to the given
* array; must be non-negative and no larger than
* <tt>dst.length - offset</tt>
* @return This buffer
* @throws BufferUnderflowException If there are fewer than <tt>length</tt> bytes
* remaining in this buffer
* @throws IndexOutOfBoundsException If the preconditions on the <tt>offset</tt> and <tt>length</tt>
* parameters do not hold
*/
public ByteBuffer get(byte[] dst, int offset, int length) {
checkBounds(offset, length, dst.length);
if (length > remaining())
throw new BufferUnderflowException();
int end = offset + length;
for (int i = offset; i < end; i++)
dst[i] = get();
return this;
}
/**
* Relative bulk <i>get</i> method.
*
* <p> This method transfers bytes from this buffer into the given
* destination array. An invocation of this method of the form
* <tt>src.get(a)</tt> behaves in exactly the same way as the invocation
*
* <pre>
* src.get(a, 0, a.length) </pre>
*
* @param dst The destination array
* @return This buffer
* @throws BufferUnderflowException If there are fewer than <tt>length</tt> bytes
* remaining in this buffer
*/
public ByteBuffer get(byte[] dst) {
return get(dst, 0, dst.length);
}
// -- Bulk put operations --
/**
* Relative bulk <i>put</i> method <i>(optional operation)</i>.
*
* <p> This method transfers the bytes remaining in the given source
* buffer into this buffer. If there are more bytes remaining in the
* source buffer than in this buffer, that is, if
* <tt>src.remaining()</tt> <tt>></tt> <tt>remaining()</tt>,
* then no bytes are transferred and a {@link
* BufferOverflowException} is thrown.
*
* <p> Otherwise, this method copies
* <i>n</i> = <tt>src.remaining()</tt> bytes from the given
* buffer into this buffer, starting at each buffer's current position.
* The positions of both buffers are then incremented by <i>n</i>.
*
* <p> In other words, an invocation of this method of the form
* <tt>dst.put(src)</tt> has exactly the same effect as the loop
*
* <pre>
* while (src.hasRemaining())
* dst.put(src.get()); </pre>
* <p>
* except that it first checks that there is sufficient space in this
* buffer and it is potentially much more efficient.
*
* @param src The source buffer from which bytes are to be read;
* must not be this buffer
* @return This buffer
* @throws BufferOverflowException If there is insufficient space in this buffer
* for the remaining bytes in the source buffer
* @throws IllegalArgumentException If the source buffer is this buffer
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public ByteBuffer put(ByteBuffer src) {
if (src == this)
throw new IllegalArgumentException();
if (isReadOnly())
throw new ReadOnlyBufferException();
int n = src.remaining();
if (n > remaining())
throw new BufferOverflowException();
for (int i = 0; i < n; i++)
put(src.get());
return this;
}
/**
* Relative bulk <i>put</i> method <i>(optional operation)</i>.
*
* <p> This method transfers bytes into this buffer from the given
* source array. If there are more bytes to be copied from the array
* than remain in this buffer, that is, if
* <tt>length</tt> <tt>></tt> <tt>remaining()</tt>, then no
* bytes are transferred and a {@link BufferOverflowException} is
* thrown.
*
* <p> Otherwise, this method copies <tt>length</tt> bytes from the
* given array into this buffer, starting at the given offset in the array
* and at the current position of this buffer. The position of this buffer
* is then incremented by <tt>length</tt>.
*
* <p> In other words, an invocation of this method of the form
* <tt>dst.put(src, off, len)</tt> has exactly the same effect as
* the loop
*
* <pre>{@code
* for (int i = off; i < off + len; i++)
* dst.put(a[i]);
* }</pre>
* <p>
* except that it first checks that there is sufficient space in this
* buffer and it is potentially much more efficient.
*
* @param src The array from which bytes are to be read
* @param offset The offset within the array of the first byte to be read;
* must be non-negative and no larger than <tt>array.length</tt>
* @param length The number of bytes to be read from the given array;
* must be non-negative and no larger than
* <tt>array.length - offset</tt>
* @return This buffer
* @throws BufferOverflowException If there is insufficient space in this buffer
* @throws IndexOutOfBoundsException If the preconditions on the <tt>offset</tt> and <tt>length</tt>
* parameters do not hold
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public ByteBuffer put(byte[] src, int offset, int length) {
checkBounds(offset, length, src.length);
if (length > remaining())
throw new BufferOverflowException();
int end = offset + length;
for (int i = offset; i < end; i++)
this.put(src[i]);
return this;
}
/**
* Relative bulk <i>put</i> method <i>(optional operation)</i>.
*
* <p> This method transfers the entire content of the given source
* byte array into this buffer. An invocation of this method of the
* form <tt>dst.put(a)</tt> behaves in exactly the same way as the
* invocation
*
* <pre>
* dst.put(a, 0, a.length) </pre>
*
* @param src The source array
* @return This buffer
* @throws BufferOverflowException If there is insufficient space in this buffer
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public final ByteBuffer put(byte[] src) {
return put(src, 0, src.length);
}
// -- Other stuff --
/**
* Tells whether or not this buffer is backed by an accessible byte
* array.
*
* <p> If this method returns <tt>true</tt> then the {@link #array() array}
* and {@link #arrayOffset() arrayOffset} methods may safely be invoked.
* </p>
*
* @return <tt>true</tt> if, and only if, this buffer
* is backed by an array and is not read-only
*/
public final boolean hasArray() {
return (hb != null) && !isReadOnly;
}
/**
* Returns the byte array that backs this
* buffer <i>(optional operation)</i>.
*
* <p> Modifications to this buffer's content will cause the returned
* array's content to be modified, and vice versa.
*
* <p> Invoke the {@link #hasArray hasArray} method before invoking this
* method in order to ensure that this buffer has an accessible backing
* array. </p>
*
* @return The array that backs this buffer
* @throws ReadOnlyBufferException If this buffer is backed by an array but is read-only
* @throws UnsupportedOperationException If this buffer is not backed by an accessible array
*/
public final byte[] array() {
if (hb == null)
throw new UnsupportedOperationException();
if (isReadOnly)
throw new ReadOnlyBufferException();
return hb;
}
/**
* Returns the offset within this buffer's backing array of the first
* element of the buffer <i>(optional operation)</i>.
*
* <p> If this buffer is backed by an array then buffer position <i>p</i>
* corresponds to array index <i>p</i> + <tt>arrayOffset()</tt>.
*
* <p> Invoke the {@link #hasArray hasArray} method before invoking this
* method in order to ensure that this buffer has an accessible backing
* array. </p>
*
* @return The offset within this buffer's array
* of the first element of the buffer
* @throws ReadOnlyBufferException If this buffer is backed by an array but is read-only
* @throws UnsupportedOperationException If this buffer is not backed by an accessible array
*/
public final int arrayOffset() {
if (hb == null)
throw new UnsupportedOperationException();
if (isReadOnly)
throw new ReadOnlyBufferException();
return offset;
}
/**
* Compacts this buffer <i>(optional operation)</i>.
*
* <p> The bytes between the buffer's current position and its limit,
* if any, are copied to the beginning of the buffer. That is, the
* byte at index <i>p</i> = <tt>position()</tt> is copied
* to index zero, the byte at index <i>p</i> + 1 is copied
* to index one, and so forth until the byte at index
* <tt>limit()</tt> - 1 is copied to index
* <i>n</i> = <tt>limit()</tt> - <tt>1</tt> - <i>p</i>.
* The buffer's position is then set to <i>n+1</i> and its limit is set to
* its capacity. The mark, if defined, is discarded.
*
* <p> The buffer's position is set to the number of bytes copied,
* rather than to zero, so that an invocation of this method can be
* followed immediately by an invocation of another relative <i>put</i>
* method. </p>
*
*
*
* <p> Invoke this method after writing data from a buffer in case the
* write was incomplete. The following loop, for example, copies bytes
* from one channel to another via the buffer <tt>buf</tt>:
*
* <blockquote><pre>{@code
* buf.clear(); // Prepare buffer for use
* while (in.read(buf) >= 0 || buf.position != 0) {
* buf.flip();
* out.write(buf);
* buf.compact(); // In case of partial write
* }
* }</pre></blockquote>
*
* @return This buffer
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer compact();
/**
* Tells whether or not this byte buffer is direct.
*
* @return <tt>true</tt> if, and only if, this buffer is direct
*/
public abstract boolean isDirect();
/**
* Returns a string summarizing the state of this buffer.
*
* @return A summary string
*/
public String toString() {
StringBuffer sb = new StringBuffer();
sb.append(getClass().getName());
sb.append("[pos=");
sb.append(position());
sb.append(" lim=");
sb.append(limit());
sb.append(" cap=");
sb.append(capacity());
sb.append("]");
return sb.toString();
}
/**
* Returns the current hash code of this buffer.
*
* <p> The hash code of a byte buffer depends only upon its remaining
* elements; that is, upon the elements from <tt>position()</tt> up to, and
* including, the element at <tt>limit()</tt> - <tt>1</tt>.
*
* <p> Because buffer hash codes are content-dependent, it is inadvisable
* to use buffers as keys in hash maps or similar data structures unless it
* is known that their contents will not change. </p>
*
* @return The current hash code of this buffer
*/
public int hashCode() {
int h = 1;
int p = position();
for (int i = limit() - 1; i >= p; i--)
h = 31 * h + (int) get(i);
return h;
}
/**
* Tells whether or not this buffer is equal to another object.
*
* <p> Two byte buffers are equal if, and only if,
*
* <ol>
*
* <li><p> They have the same element type, </p></li>
*
* <li><p> They have the same number of remaining elements, and
* </p></li>
*
* <li><p> The two sequences of remaining elements, considered
* independently of their starting positions, are pointwise equal.
*
* <p> A byte buffer is not equal to any other type of object. </p>
*
* @param ob The object to which this buffer is to be compared
* @return <tt>true</tt> if, and only if, this buffer is equal to the
* given object
*/
public boolean equals(Object ob) {
if (this == ob)
return true;
if (!(ob instanceof ByteBuffer))
return false;
ByteBuffer that = (ByteBuffer) ob;
if (this.remaining() != that.remaining())
return false;
int p = this.position();
for (int i = this.limit() - 1, j = that.limit() - 1; i >= p; i--, j--)
if (!equals(this.get(i), that.get(j)))
return false;
return true;
}
private static boolean equals(byte x, byte y) {
return x == y;
}
/**
* Compares this buffer to another.
*
* <p> Two byte buffers are compared by comparing their sequences of
* remaining elements lexicographically, without regard to the starting
* position of each sequence within its corresponding buffer.
* <p>
* Pairs of {@code byte} elements are compared as if by invoking
* {@link Byte#compare(byte, byte)}.
*
* <p> A byte buffer is not comparable to any other type of object.
*
* @return A negative integer, zero, or a positive integer as this buffer
* is less than, equal to, or greater than the given buffer
*/
public int compareTo(ByteBuffer that) {
int n = this.position() + Math.min(this.remaining(), that.remaining());
for (int i = this.position(), j = that.position(); i < n; i++, j++) {
int cmp = compare(this.get(i), that.get(j));
if (cmp != 0)
return cmp;
}
return this.remaining() - that.remaining();
}
private static int compare(byte x, byte y) {
return Byte.compare(x, y);
}
// -- Other char stuff --
// -- Other byte stuff: Access to binary data --
boolean bigEndian = true;
boolean nativeByteOrder = (Bits.byteOrder() == ByteOrder.BIG_ENDIAN);
/**
* Retrieves this buffer's byte order.
*
* <p> The byte order is used when reading or writing multibyte values, and
* when creating buffers that are views of this byte buffer. The order of
* a newly-created byte buffer is always {@link ByteOrder#BIG_ENDIAN
* BIG_ENDIAN}. </p>
*
* @return This buffer's byte order
*/
public final ByteOrder order() {
return bigEndian ? ByteOrder.BIG_ENDIAN : ByteOrder.LITTLE_ENDIAN;
}
/**
* Modifies this buffer's byte order.
*
* @param bo The new byte order,
* either {@link ByteOrder#BIG_ENDIAN BIG_ENDIAN}
* or {@link ByteOrder#LITTLE_ENDIAN LITTLE_ENDIAN}
* @return This buffer
*/
public final ByteBuffer order(ByteOrder bo) {
bigEndian = (bo == ByteOrder.BIG_ENDIAN);
nativeByteOrder =
(bigEndian == (Bits.byteOrder() == ByteOrder.BIG_ENDIAN));
return this;
}
// Unchecked accessors, for use by ByteBufferAs-X-Buffer classes
//
abstract byte _get(int i); // package-private
abstract void _put(int i, byte b); // package-private
/**
* Relative <i>get</i> method for reading a char value.
*
* <p> Reads the next two bytes at this buffer's current position,
* composing them into a char value according to the current byte order,
* and then increments the position by two. </p>
*
* @return The char value at the buffer's current position
* @throws BufferUnderflowException If there are fewer than two bytes
* remaining in this buffer
*/
public abstract char getChar();
/**
* Relative <i>put</i> method for writing a char
* value <i>(optional operation)</i>.
*
* <p> Writes two bytes containing the given char value, in the
* current byte order, into this buffer at the current position, and then
* increments the position by two. </p>
*
* @param value The char value to be written
* @return This buffer
* @throws BufferOverflowException If there are fewer than two bytes
* remaining in this buffer
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putChar(char value);
/**
* Absolute <i>get</i> method for reading a char value.
*
* <p> Reads two bytes at the given index, composing them into a
* char value according to the current byte order. </p>
*
* @param index The index from which the bytes will be read
* @return The char value at the given index
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus one
*/
public abstract char getChar(int index);
/**
* Absolute <i>put</i> method for writing a char
* value <i>(optional operation)</i>.
*
* <p> Writes two bytes containing the given char value, in the
* current byte order, into this buffer at the given index. </p>
*
* @param index The index at which the bytes will be written
* @param value The char value to be written
* @return This buffer
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus one
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putChar(int index, char value);
/**
* Creates a view of this byte buffer as a char buffer.
*
* <p> The content of the new buffer will start at this buffer's current
* position. Changes to this buffer's content will be visible in the new
* buffer, and vice versa; the two buffers' position, limit, and mark
* values will be independent.
*
* <p> The new buffer's position will be zero, its capacity and its limit
* will be the number of bytes remaining in this buffer divided by
* two, and its mark will be undefined. The new buffer will be direct
* if, and only if, this buffer is direct, and it will be read-only if, and
* only if, this buffer is read-only. </p>
*
* @return A new char buffer
*/
public abstract CharBuffer asCharBuffer();
/**
* Relative <i>get</i> method for reading a short value.
*
* <p> Reads the next two bytes at this buffer's current position,
* composing them into a short value according to the current byte order,
* and then increments the position by two. </p>
*
* @return The short value at the buffer's current position
* @throws BufferUnderflowException If there are fewer than two bytes
* remaining in this buffer
*/
public abstract short getShort();
/**
* Relative <i>put</i> method for writing a short
* value <i>(optional operation)</i>.
*
* <p> Writes two bytes containing the given short value, in the
* current byte order, into this buffer at the current position, and then
* increments the position by two. </p>
*
* @param value The short value to be written
* @return This buffer
* @throws BufferOverflowException If there are fewer than two bytes
* remaining in this buffer
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putShort(short value);
/**
* Absolute <i>get</i> method for reading a short value.
*
* <p> Reads two bytes at the given index, composing them into a
* short value according to the current byte order. </p>
*
* @param index The index from which the bytes will be read
* @return The short value at the given index
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus one
*/
public abstract short getShort(int index);
/**
* Absolute <i>put</i> method for writing a short
* value <i>(optional operation)</i>.
*
* <p> Writes two bytes containing the given short value, in the
* current byte order, into this buffer at the given index. </p>
*
* @param index The index at which the bytes will be written
* @param value The short value to be written
* @return This buffer
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus one
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putShort(int index, short value);
/**
* Creates a view of this byte buffer as a short buffer.
*
* <p> The content of the new buffer will start at this buffer's current
* position. Changes to this buffer's content will be visible in the new
* buffer, and vice versa; the two buffers' position, limit, and mark
* values will be independent.
*
* <p> The new buffer's position will be zero, its capacity and its limit
* will be the number of bytes remaining in this buffer divided by
* two, and its mark will be undefined. The new buffer will be direct
* if, and only if, this buffer is direct, and it will be read-only if, and
* only if, this buffer is read-only. </p>
*
* @return A new short buffer
*/
public abstract ShortBuffer asShortBuffer();
/**
* Relative <i>get</i> method for reading an int value.
*
* <p> Reads the next four bytes at this buffer's current position,
* composing them into an int value according to the current byte order,
* and then increments the position by four. </p>
*
* @return The int value at the buffer's current position
* @throws BufferUnderflowException If there are fewer than four bytes
* remaining in this buffer
*/
public abstract int getInt();
/**
* Relative <i>put</i> method for writing an int
* value <i>(optional operation)</i>.
*
* <p> Writes four bytes containing the given int value, in the
* current byte order, into this buffer at the current position, and then
* increments the position by four. </p>
*
* @param value The int value to be written
* @return This buffer
* @throws BufferOverflowException If there are fewer than four bytes
* remaining in this buffer
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putInt(int value);
/**
* Absolute <i>get</i> method for reading an int value.
*
* <p> Reads four bytes at the given index, composing them into a
* int value according to the current byte order. </p>
*
* @param index The index from which the bytes will be read
* @return The int value at the given index
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus three
*/
public abstract int getInt(int index);
/**
* Absolute <i>put</i> method for writing an int
* value <i>(optional operation)</i>.
*
* <p> Writes four bytes containing the given int value, in the
* current byte order, into this buffer at the given index. </p>
*
* @param index The index at which the bytes will be written
* @param value The int value to be written
* @return This buffer
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus three
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putInt(int index, int value);
/**
* Creates a view of this byte buffer as an int buffer.
*
* <p> The content of the new buffer will start at this buffer's current
* position. Changes to this buffer's content will be visible in the new
* buffer, and vice versa; the two buffers' position, limit, and mark
* values will be independent.
*
* <p> The new buffer's position will be zero, its capacity and its limit
* will be the number of bytes remaining in this buffer divided by
* four, and its mark will be undefined. The new buffer will be direct
* if, and only if, this buffer is direct, and it will be read-only if, and
* only if, this buffer is read-only. </p>
*
* @return A new int buffer
*/
public abstract IntBuffer asIntBuffer();
/**
* Relative <i>get</i> method for reading a long value.
*
* <p> Reads the next eight bytes at this buffer's current position,
* composing them into a long value according to the current byte order,
* and then increments the position by eight. </p>
*
* @return The long value at the buffer's current position
* @throws BufferUnderflowException If there are fewer than eight bytes
* remaining in this buffer
*/
public abstract long getLong();
/**
* Relative <i>put</i> method for writing a long
* value <i>(optional operation)</i>.
*
* <p> Writes eight bytes containing the given long value, in the
* current byte order, into this buffer at the current position, and then
* increments the position by eight. </p>
*
* @param value The long value to be written
* @return This buffer
* @throws BufferOverflowException If there are fewer than eight bytes
* remaining in this buffer
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putLong(long value);
/**
* Absolute <i>get</i> method for reading a long value.
*
* <p> Reads eight bytes at the given index, composing them into a
* long value according to the current byte order. </p>
*
* @param index The index from which the bytes will be read
* @return The long value at the given index
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus seven
*/
public abstract long getLong(int index);
/**
* Absolute <i>put</i> method for writing a long
* value <i>(optional operation)</i>.
*
* <p> Writes eight bytes containing the given long value, in the
* current byte order, into this buffer at the given index. </p>
*
* @param index The index at which the bytes will be written
* @param value The long value to be written
* @return This buffer
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus seven
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putLong(int index, long value);
/**
* Creates a view of this byte buffer as a long buffer.
*
* <p> The content of the new buffer will start at this buffer's current
* position. Changes to this buffer's content will be visible in the new
* buffer, and vice versa; the two buffers' position, limit, and mark
* values will be independent.
*
* <p> The new buffer's position will be zero, its capacity and its limit
* will be the number of bytes remaining in this buffer divided by
* eight, and its mark will be undefined. The new buffer will be direct
* if, and only if, this buffer is direct, and it will be read-only if, and
* only if, this buffer is read-only. </p>
*
* @return A new long buffer
*/
public abstract LongBuffer asLongBuffer();
/**
* Relative <i>get</i> method for reading a float value.
*
* <p> Reads the next four bytes at this buffer's current position,
* composing them into a float value according to the current byte order,
* and then increments the position by four. </p>
*
* @return The float value at the buffer's current position
* @throws BufferUnderflowException If there are fewer than four bytes
* remaining in this buffer
*/
public abstract float getFloat();
/**
* Relative <i>put</i> method for writing a float
* value <i>(optional operation)</i>.
*
* <p> Writes four bytes containing the given float value, in the
* current byte order, into this buffer at the current position, and then
* increments the position by four. </p>
*
* @param value The float value to be written
* @return This buffer
* @throws BufferOverflowException If there are fewer than four bytes
* remaining in this buffer
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putFloat(float value);
/**
* Absolute <i>get</i> method for reading a float value.
*
* <p> Reads four bytes at the given index, composing them into a
* float value according to the current byte order. </p>
*
* @param index The index from which the bytes will be read
* @return The float value at the given index
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus three
*/
public abstract float getFloat(int index);
/**
* Absolute <i>put</i> method for writing a float
* value <i>(optional operation)</i>.
*
* <p> Writes four bytes containing the given float value, in the
* current byte order, into this buffer at the given index. </p>
*
* @param index The index at which the bytes will be written
* @param value The float value to be written
* @return This buffer
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus three
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putFloat(int index, float value);
/**
* Creates a view of this byte buffer as a float buffer.
*
* <p> The content of the new buffer will start at this buffer's current
* position. Changes to this buffer's content will be visible in the new
* buffer, and vice versa; the two buffers' position, limit, and mark
* values will be independent.
*
* <p> The new buffer's position will be zero, its capacity and its limit
* will be the number of bytes remaining in this buffer divided by
* four, and its mark will be undefined. The new buffer will be direct
* if, and only if, this buffer is direct, and it will be read-only if, and
* only if, this buffer is read-only. </p>
*
* @return A new float buffer
*/
public abstract FloatBuffer asFloatBuffer();
/**
* Relative <i>get</i> method for reading a double value.
*
* <p> Reads the next eight bytes at this buffer's current position,
* composing them into a double value according to the current byte order,
* and then increments the position by eight. </p>
*
* @return The double value at the buffer's current position
* @throws BufferUnderflowException If there are fewer than eight bytes
* remaining in this buffer
*/
public abstract double getDouble();
/**
* Relative <i>put</i> method for writing a double
* value <i>(optional operation)</i>.
*
* <p> Writes eight bytes containing the given double value, in the
* current byte order, into this buffer at the current position, and then
* increments the position by eight. </p>
*
* @param value The double value to be written
* @return This buffer
* @throws BufferOverflowException If there are fewer than eight bytes
* remaining in this buffer
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putDouble(double value);
/**
* Absolute <i>get</i> method for reading a double value.
*
* <p> Reads eight bytes at the given index, composing them into a
* double value according to the current byte order. </p>
*
* @param index The index from which the bytes will be read
* @return The double value at the given index
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus seven
*/
public abstract double getDouble(int index);
/**
* Absolute <i>put</i> method for writing a double
* value <i>(optional operation)</i>.
*
* <p> Writes eight bytes containing the given double value, in the
* current byte order, into this buffer at the given index. </p>
*
* @param index The index at which the bytes will be written
* @param value The double value to be written
* @return This buffer
* @throws IndexOutOfBoundsException If <tt>index</tt> is negative
* or not smaller than the buffer's limit,
* minus seven
* @throws ReadOnlyBufferException If this buffer is read-only
*/
public abstract ByteBuffer putDouble(int index, double value);
/**
* Creates a view of this byte buffer as a double buffer.
*
* <p> The content of the new buffer will start at this buffer's current
* position. Changes to this buffer's content will be visible in the new
* buffer, and vice versa; the two buffers' position, limit, and mark
* values will be independent.
*
* <p> The new buffer's position will be zero, its capacity and its limit
* will be the number of bytes remaining in this buffer divided by
* eight, and its mark will be undefined. The new buffer will be direct
* if, and only if, this buffer is direct, and it will be read-only if, and
* only if, this buffer is read-only. </p>
*
* @return A new double buffer
*/
public abstract DoubleBuffer asDoubleBuffer();
}
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