Java 中的CharArrayReader 介绍_动力节点Java学院整理

CharArrayReader(char[] buf)
CharArrayReader(char[] buf, int offset, int length)
void   close()
void   mark(int readLimit)
boolean  markSupported()
int    read()
int    read(char[] buffer, int offset, int len)
boolean  ready()
void   reset()
long   skip(long charCount)

 package java.io;
 public abstract class Reader implements Readable, Closeable {
   protected Object lock;
   protected Reader() {
     this.lock = this;
   }
   protected Reader(Object lock) {
     if (lock == null) {
       throw new NullPointerException();
     }
     this.lock = lock;
   }
   public int read(java.nio.CharBuffer target) throws IOException {
     int len = target.remaining();
     char[] cbuf = new char[len];
     int n = read(cbuf, 0, len);
     if (n > 0)
       target.put(cbuf, 0, n);
     return n;
   }
   public int read() throws IOException {
    char cb[] = new char[1];
     if (read(cb, 0, 1) == -1)
       return -1;
     else
       return cb[0];
   }
   public int read(char cbuf[]) throws IOException {
     return read(cbuf, 0, cbuf.length);
   }
   abstract public int read(char cbuf[], int off, int len) throws IOException;
   private static final int maxSkipBufferSize = 8192;
   private char skipBuffer[] = null;
   public long skip(long n) throws IOException {
     if (n < L)
       throw new IllegalArgumentException("skip value is negative");
     int nn = (int) Math.min(n, maxSkipBufferSize);
     synchronized (lock) {
       if ((skipBuffer == null) || (skipBuffer.length < nn))
       while (r > 0) {
        int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
        if (nc == -1)
           break;
         r -= nc;
       }
       return n - r;
     }
   }
   public boolean ready() throws IOException {
     return false;
   }
   public boolean markSupported() {
     return false;
   }
   public void mark(int readAheadLimit) throws IOException {
     throw new IOException("mark() not supported");
   }
   public void reset() throws IOException {
     throw new IOException("reset() not supported");
   }
   abstract public void close() throws IOException;
 }

  package java.io;
  public class CharArrayReader extends Reader {
    // 字符数组缓冲
    protected char buf[];
    // 下一个被获取的字符的位置
    protected int pos;
   // 被标记的位置
   protected int markedPos = 0;
   // 字符缓冲的长度
   protected int count;
   // 构造函数
   public CharArrayReader(char buf[]) {
     this.buf = buf;
     this.pos = 0;
     this.count = buf.length;
   }
   // 构造函数
     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;
   }
   // 判断“CharArrayReader是否有效”。
   // 若字符缓冲为null，则认为其无效。
   private void ensureOpen() throws IOException {
     if (buf == null)
       throw new IOException("Stream closed");
   }
   // 读取下一个字符。即返回字符缓冲区中下一位置的值。
   // 注意：读取的是字符！
   public int read() throws IOException {
     synchronized (lock) {
       ensureOpen();
       if (pos >= count)
         return -1;
       else
         return buf[pos++];
     }
   }
   // 读取数据，并保存到字符数组b中从off开始的位置中，len是读取长度。
   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 -;
       }
       if (pos + len > count) {
         len = count - pos;
       }
      if (len <= 0) {
        return 0;
       }
       System.arraycopy(buf, pos, b, off, len);
       pos += len;
       return len;
     }
   }
   // 跳过n个字符
   public long skip(long n) throws IOException {
     synchronized (lock) {
       ensureOpen();
       if (pos + n > count) {
         n = count - pos;
       }
       if (n < 0) {
         return 0;
       }
       pos += n;
       return n;
     }
   }
   // 判断“是否能读取下一个字符”。能的话，返回true。
   public boolean ready() throws IOException {
     synchronized (lock) {
       ensureOpen();
       return (count - pos) > ;
     }
   }
   public boolean markSupported() {
     return true;
   }
   // 保存当前位置。readAheadLimit在此处没有任何实际意义
   // mark()必须和reset()配合使用才有意义！
   public void mark(int readAheadLimit) throws IOException {
     synchronized (lock) {
       ensureOpen();
       markedPos = pos;
     }
   }
   // 重置“下一个读取位置”为“mark所标记的位置”
   public void reset() throws IOException {
     synchronized (lock) {
       ensureOpen();
       pos = markedPos;
     }
   }
   public void close() {
     buf = null;
   }
 }

 /**
  * CharArrayReader 演示程序
  *
  * 
  */
 import java.io.CharArrayReader;
 import java.io.CharArrayWriter;
 import java.io.IOException;
 public class CharArrayReaderTest {
   private static final int LEN = 5;
   // 对应英文字母“abcdefghijklmnopqrstuvwxyz”
   private static final char[] ArrayLetters = new char[] {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
   public static void main(String[] args) {
     tesCharArrayReader() ;
   }
   /**
   * CharArrayReader的API测试函数
   */
   private static void tesCharArrayReader() {
     try {
       // 创建CharArrayReader字符流，内容是ArrayLetters数组
       CharArrayReader car = new CharArrayReader(ArrayLetters);
      // 从字符数组流中读取5个字符
       for (int i=; i<LEN; i++) {
         // 若能继续读取下一个字符，则读取下一个字符
         if (car.ready() == true) {
           // 读取“字符流的下一个字符”
           char tmp = (char)car.read();
           System.out.printf("%d : %c\n", i, tmp);
         }
       }
       // 若“该字符流”不支持标记功能，则直接退出
       if (!car.markSupported()) {
         System.out.println("make not supported!");
         return ;
       }
      // 标记“字符流中下一个被读取的位置”。即--标记“f”，因为因为前面已经读取了5个字符，所以下一个被读取的位置是第6个字符”
      // (01), CharArrayReader类的mark(0)函数中的“参数0”是没有实际意义的。
      // (02), mark()与reset()是配套的，reset()会将“字符流中下一个被读取的位置”重置为“mark()中所保存的位置”
      car.mark(0);
      // 跳过5个字符。跳过5个字符后，字符流中下一个被读取的值应该是“k”。
       car.skip(5);
       // 从字符流中读取个数据。即读取“klmno”
       char[] buf = new char[LEN];
      car.read(buf, 0, LEN);
       System.out.printf("buf=%s\n", String.valueOf(buf));
       // 重置“字符流”：即，将“字符流中下一个被读取的位置”重置到“mark()所标记的位置”，即f。
       car.reset();
       // 从“重置后的字符流”中读取5个字符到buf中。即读取“fghij”
      car.read(buf, 0, LEN);
       System.out.printf("buf=%s\n", String.valueOf(buf));
     } catch (IOException e) {
       e.printStackTrace();
     }
   }
 }

0 : a
1 : b
2 : c
3 : d
4 : e
buf=klmno
buf=fghij