Java 7之传统I/O - 字符类 CharArrayReader和CharArrayWriter

CharArrayReader和CharArrayWriter是字符数组流。它和ByteArrayInputStream、ByteArrayOutputStream类似，只不过ByteArrayXXputStream是字节数组流，而CharArrayXX是字符数组流。

CharArrayWriter是用于读取字符数组，它继承于Writer类。以字符为单位进行数组的操作。下面来看一下主要方法实现的源代码：

1、创建及初始化

看一下CharArrayWritrer中定义的重要变量及构造函数：

    protected char buf[];  // 字符数组,用于数组的存取     protected int count;   // 数组中数据元素个数    public CharArrayWriter() {        this(32);    }    public CharArrayWriter(int initialSize) {        if (initialSize < 0) {            throw new IllegalArgumentException("Negative initial size: " + initialSize);        }        buf = new char[initialSize];    }

默认buf数组的大小为32，也可以自己进行指定。

CharArrayReader中定义的重要变量及构造函数：

    protected char buf[];         // 字符数组,用于数组的存取    protected int pos;            // 当前读取的位置    protected int markedPos = 0;  // 设置的标识位        protected int count;          // 数组中数据元素个数    public CharArrayReader(char buf[]) {        this.buf = buf;        this.pos = 0;        this.count = buf.length;    }    public CharArrayReader(char buf[], int offset, int length) {        if ((offset < 0) || (offset > buf.length) || (length < 0) || ((offset + length) < 0)) {            throw new IllegalArgumentException();        }        this.buf = buf;        this.pos = offset;        this.count = Math.min(offset + length, buf.length);        this.markedPos = offset;    }

2、CharArrayWritrer写入数据

    public void write(int c) {        synchronized (lock) {            int newcount = count + 1;            if (newcount > buf.length) {                buf = Arrays.copyOf(buf, Math.max(buf.length << 1, newcount));            }            buf[count] = (char)c;            count = newcount;        }    }    public void write(char c[], int off, int len) {        if ((off < 0) || (off > c.length) || (len < 0) || ((off + len) > c.length) || ((off + len) < 0)) {            throw new IndexOutOfBoundsException();        } else if (len == 0) {            return;        }        synchronized (lock) {            int newcount = count + len;            if (newcount > buf.length) {                buf = Arrays.copyOf(buf, Math.max(buf.length << 1, newcount));            }            System.arraycopy(c, off, buf, count, len);            count = newcount;        }    }    public void write(String str, int off, int len) {        synchronized (lock) {            int newcount = count + len;            if (newcount > buf.length) {                buf = Arrays.copyOf(buf, Math.max(buf.length << 1, newcount));            }            str.getChars(off, off + len, buf, count);            count = newcount;        }    }

实现了Write类中定义的write()方法和append()方法。其实现代码还是比较简单的，在前面类似的方法已经说过多遍了，这里不再赘述。

3、CharArrayReader读取数据

CharArrayReader 是用于读取字符数组，它继承于Reader。操作的数据是以字符为单位。下面来看一下主要方法实现的源代码：

    public int read() throws IOException {        synchronized (lock) {            ensureOpen();            if (pos >= count)                return -1;            else                return buf[pos++];        }    }    public int read(char b[], int off, int len) throws IOException {        synchronized (lock) {            ensureOpen();            if ((off < 0) || (off > b.length) || (len < 0) ||                ((off + len) > b.length) || ((off + len) < 0)) {                throw new IndexOutOfBoundsException();            } else if (len == 0) {                return 0;            }            if (pos >= count) {                return -1;            }            if (pos + len > count) {                len = count - pos;            }            if (len <= 0) {                return 0;            }            System.arraycopy(buf, pos, b, off, len);            pos += len;            return len;        }    }

与操作字符串的类StringReader、StringWriter类似，其实字符数组与字符串操作有相通性，字符串在底层实际上就是由字符数组来实现的。如果理解了StringReader和StringWriter类，这个类会非常容易理解。另外提醒一点，这两个类也是线程安全的。

下面来编写一个简单的测试程序：

       char[] x={'a','d','p'};       CharArrayWriter cw=new CharArrayWriter();       cw.write(x,0,2);       cw.append("x");       System.out.println(cw.toString()); // adx              CharArrayReader cr=new CharArrayReader(cw.toCharArray());       System.out.println((char)cr.read());// a