Java基础知识之CharArrayReader流的使用

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/**
     * 利用指定字符数组创建CharArrayReader对象
     * 本质是将字符数组赋值给对象的字符缓冲区
     */
    public CharArrayReader(char buf[]) {
        this.buf = buf;
        this.pos = 0;
        this.count = buf.length;
    }

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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;
    }

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/** 字符缓冲区 */
    protected char buf[];
 
    /** 缓冲区当前位置 */
    protected int pos;
 
    /** 标记在缓冲区中的位置 */
    protected int markedPos = 0;
 
    /**
     * 缓冲区结束的索引，该索引或者之外没有有效数据
     * 即缓冲区的长度值
     */
    protected int count;

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public int read() throws IOException {
        synchronized (lock) {
            ensureOpen();
            if (pos >= count) //当前位置大于等于结束索引时，代表缓冲区内容已读取到尾部，返回-1
                return -1;
            else
                return buf[pos++];   //直接换回缓冲区字符
        }
    }

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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) { //字符缓冲区数据已读取完毕
                return -1;
            }
            if (pos + len > count) { //字符缓冲区当前位置读取len个字节后超出界限的话，则只读当前位置到结束索引的字节
                len = count - pos;
            }
            if (len <= 0) {         //感觉此if多余
                return 0;
            }
            System.arraycopy(buf, pos, b, off, len); //从字符缓冲区中读取len个字节到目标数组中
            pos += len; //修改字符缓冲区当前位置
            return len;
        }
    }

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/**
     *关闭流并释放资源--本质是将缓冲区赋值为null,则该流其它方法都不能使用
     *根本就没有调用过系统资源，因此关闭是无效的？但是一旦关闭在调用其他方法，就会抛异常
     */
    public void close() {
        buf = null;
    }
 
   /** 确保流不被关闭 */
    private void ensureOpen() throws IOException {
        if (buf == null)
            throw new IOException("Stream closed");
    }

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CharArrayReader(char array[ ]) 
CharArrayReader(char array[ ], int start, int numChars)

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// Demonstrate CharArrayReader. 
import java.io.*; 
public class CharArrayReaderDemo { 
 public static void main(String args[]) throws IOException { 
 String tmp = "abcdefghijklmnopqrstuvwxyz"; 
 int length = tmp.length(); 
 char c[] = new char[length]; 
 tmp.getChars(0, length, c, 0); 
 CharArrayReader input1 = new CharArrayReader(c); 
 CharArrayReader input2 = new CharArrayReader(c, 0, 5); 
 int i; 
 System.out.println("input1 is:"); 
 while((i = input1.read()) != -1) { 
 System.out.print((char)i); 
 } 
 System.out.println(); 
 System.out.println("input2 is:"); 
 while((i = input2.read()) != -1) { 
 System.out.print((char)i); 
 } 
 System.out.println(); 
 } 
}