/* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package java.nio;
/**
* A buffer is a list of elements of a specific primitive type.
* <p>
* A buffer can be described by the following properties:
* <ul>
* <li>Capacity: the number of elements a buffer can hold. Capacity may not be
* negative and never changes.</li>
* <li>Position: a cursor of this buffer. Elements are read or written at the
* position if you do not specify an index explicitly. Position may not be
* negative and not greater than the limit.</li>
* <li>Limit: controls the scope of accessible elements. You can only read or
* write elements from index zero to <code>limit - 1</code>. Accessing
* elements out of the scope will cause an exception. Limit may not be negative
* and not greater than capacity.</li>
* <li>Mark: used to remember the current position, so that you can reset the
* position later. Mark may not be negative and no greater than position.</li>
* <li>A buffer can be read-only or read-write. Trying to modify the elements
* of a read-only buffer will cause a <code>ReadOnlyBufferException</code>,
* while changing the position, limit and mark of a read-only buffer is OK.</li>
* <li>A buffer can be direct or indirect. A direct buffer will try its best to
* take advantage of native memory APIs and it may not stay in the Java heap,
* thus it is not affected by garbage collection.</li>
* </ul>
* <p>
* Buffers are not thread-safe. If concurrent access to a buffer instance is
* required, then the callers are responsible to take care of the
* synchronization issues.
*/
public abstract class Buffer {
/**
* <code>UNSET_MARK</code> means the mark has not been set.
*/
final static int UNSET_MARK = -1;
/**
* The capacity of this buffer, which never change.
*/
final int capacity;
/**
* <code>limit - 1</code> is the last element that can be read or written.
* Limit must be no less than zero and no greater than <code>capacity</code>.
*/
int limit;
/**
* Mark is where position will be set when <code>reset()</code> is called.
* Mark is not set by default. Mark is always no less than zero and no
* greater than <code>position</code>.
*/
int mark = UNSET_MARK;
/**
* The current position of this buffer. Position is always no less than zero
* and no greater than <code>limit</code>.
*/
int position = 0;
// BEGIN android-added
/**
* The log base 2 of the element size of this buffer. Each typed subclass
* (ByteBuffer, CharBuffer, etc.) is responsible for initializing this
* value. The value is used by native code to avoid the need for costly
* 'instanceof' tests.
*
*/
int _elementSizeShift;
/**
* Returns the array associated with this buffer, or null if none exists.
* Each typed subclass (ByteBuffer, CharBuffer, etc.) overrides this method
* to call its array() method with appropriate checks.
*
* @return a primitive array or null
*/
Object _array() {
return null;
}
/**
* Returns the offset into the backing array, if one exists, otherwise 0.
* Each typed subclass (ByteBuffer, CharBuffer, etc.) overrides this method
* to call its arrayOffset() method with appropriate checks.
*
* @return the array offset, or 0
*/
int _arrayOffset() {
return 0;
}
/**
* For direct buffers, the effective address of the data. This is set
* on first use. If the field is zero, this is either not a direct
* buffer or the field has not been initialized, and you need to issue
* the getEffectiveAddress() call and use the result of that.
*
* This is strictly an optimization.
*/
int effectiveDirectAddress = 0;
// END android-added
/**
* Construct a buffer with the specified capacity.
*
* @param capacity
* The capacity of this buffer
*/
Buffer(int capacity) {
super();
if (capacity < 0) {
throw new IllegalArgumentException();
}
this.capacity = this.limit = capacity;
}
/**
* Returns the capacity of this buffer.
*
* @return the number of elements that are contained in this buffer.
*/
public final int capacity() {
return capacity;
}
/**
* Clears this buffer.
* <p>
* While the content of this buffer is not changed, the following internal
* changes take place: the current position is reset back to the start of
* the buffer, the value of the buffer limit is made equal to the capacity
* and mark is cleared.
*
* @return this buffer.
*/
public final Buffer clear() {
position = 0;
mark = UNSET_MARK;
limit = capacity;
return this;
}
/**
* Flips this buffer.
* <p>
* The limit is set to the current position, then the position is set to
* zero, and the mark is cleared.
* <p>
* The content of this buffer is not changed.
*
* @return this buffer.
*/
public final Buffer flip() {
limit = position;
position = 0;
mark = UNSET_MARK;
return this;
}
/**
* Indicates if there are elements remaining in this buffer, that is if
* {@code position < limit}.
*
* @return {@code true} if there are elements remaining in this buffer,
* {@code false} otherwise.
*/
public final boolean hasRemaining() {
return position < limit;
}
/**
* Indicates whether this buffer is read-only.
*
* @return {@code true} if this buffer is read-only, {@code false}
* otherwise.
*/
public abstract boolean isReadOnly();
/**
* Returns the limit of this buffer.
*
* @return the limit of this buffer.
*/
public final int limit() {
return limit;
}
/**
* Sets the limit of this buffer.
* <p>
* If the current position in the buffer is in excess of
* <code>newLimit</code> then, on returning from this call, it will have
* been adjusted to be equivalent to <code>newLimit</code>. If the mark
* is set and is greater than the new limit, then it is cleared.
*
* @param newLimit
* the new limit, must not be negative and not greater than
* capacity.
* @return this buffer.
* @exception IllegalArgumentException
* if <code>newLimit</code> is invalid.
*/
public final Buffer limit(int newLimit) {
if (newLimit < 0 || newLimit > capacity) {
throw new IllegalArgumentException();
}
limit = newLimit;
if (position > newLimit) {
position = newLimit;
}
if ((mark != UNSET_MARK) && (mark > newLimit)) {
mark = UNSET_MARK;
}
return this;
}
/**
* Marks the current position, so that the position may return to this point
* later by calling <code>reset()</code>.
*
* @return this buffer.
*/
public final Buffer mark() {
mark = position;
return this;
}
/**
* Returns the position of this buffer.
*
* @return the value of this buffer's current position.
*/
public final int position() {
return position;
}
/**
* Sets the position of this buffer.
* <p>
* If the mark is set and it is greater than the new position, then it is
* cleared.
*
* @param newPosition
* the new position, must be not negative and not greater than
* limit.
* @return this buffer.
* @exception IllegalArgumentException
* if <code>newPosition</code> is invalid.
*/
public final Buffer position(int newPosition) {
if (newPosition < 0 || newPosition > limit) {
throw new IllegalArgumentException();
}
position = newPosition;
if ((mark != UNSET_MARK) && (mark > position)) {
mark = UNSET_MARK;
}
return this;
}
/**
* Returns the number of remaining elements in this buffer, that is
* {@code limit - position}.
*
* @return the number of remaining elements in this buffer.
*/
public final int remaining() {
return limit - position;
}
/**
* Resets the position of this buffer to the <code>mark</code>.
*
* @return this buffer.
* @exception InvalidMarkException
* if the mark is not set.
*/
public final Buffer reset() {
if (mark == UNSET_MARK) {
throw new InvalidMarkException();
}
position = mark;
return this;
}
/**
* Rewinds this buffer.
* <p>
* The position is set to zero, and the mark is cleared. The content of this
* buffer is not changed.
*
* @return this buffer.
*/
public final Buffer rewind() {
position = 0;
mark = UNSET_MARK;
return this;
}
}