java.nio.Buffer源码解读

版本：JDK7

package java.nio;

public abstract class Buffer {

// mark <= position <= limit <= capacity
private int mark = -1;		// 标记，一个特定的position，经过mark()方法指定Buffer中的标记，以后能够经过reset()方法恢复到这个索引位置
private int position = 0;	// 下一个要读取或写入的数据的索引
private int limit;			// 界限，表示缓冲区中可操做数据的大小，索引等于和大于limit的数据不能进行读写。
private int capacity;		// 缓冲区的容量，建立后不能修改。

// Used only by direct buffers
// NOTE: hoisted here for speed in JNI GetDirectBufferAddress
long address;

// Creates a new buffer with the given mark, position, limit, and capacity,
Buffer(int mark, int pos, int lim, int cap) {
    if (cap < 0) throw new IllegalArgumentException("Negative capacity: " + cap);
    this.capacity = cap;
    limit(lim);
    position(pos);
    if (mark >= 0) {
        if (mark > pos)
            throw new IllegalArgumentException("mark > position: (" + mark + " > " + pos + ")");
        this.mark = mark;
    }
}

public final int capacity() {
    return capacity;
}

public final int position() {
    return position;
}

// 从新设置position的值
public final Buffer position(int newPosition) {
    if ((newPosition > limit) || (newPosition < 0)) throw new IllegalArgumentException();
    position = newPosition;
    if (mark > position) mark = -1;
    return this;
}

public final int limit() {
    return limit;
}

// 从新设置limit的值：若是新limit小于position，则将position设为新limit
public final Buffer limit(int newLimit) {
    if ((newLimit > capacity) || (newLimit < 0)) throw new IllegalArgumentException();
    limit = newLimit;
    if (position > limit) position = limit;
    if (mark > limit) mark = -1;
    return this;
}

// 设置标记
public final Buffer mark() {
    mark = position;
    return this;
}

// 将position的值设置为mark
public final Buffer reset() {
    int m = mark;
    if (m < 0)
        throw new InvalidMarkException();
    position = m;
    return this;
}

// 清空缓冲区：Buffer的属性恢复到初始化状态。注意：此时缓冲区中的数据仍然存在。
public final Buffer clear() {
    position = 0;
    limit = capacity;
    mark = -1;
    return this;
}

// 将limit设为当前的position，以后将position重置为0
public final Buffer flip() {
    limit = position;
    position = 0;
    mark = -1;
    return this;
}

// 将position设为0，并取消设置的标记：即从新读Buffer
public final Buffer rewind() {
    position = 0;
    mark = -1;
    return this;
}

// 返回剩余的可用空间
public final int remaining() {
    return limit - position;
}

// 判断缓冲区中是否还有元素
public final boolean hasRemaining() {
    return position < limit;
}


public abstract boolean isReadOnly();

public abstract boolean hasArray();

public abstract Object array();

public abstract int arrayOffset();

public abstract boolean isDirect();

// -- Package-private methods for bounds checking, etc. --
// ...

}