CharArrayWriter介紹

用於寫入字元資料，繼承於writer，操作的是單位為字元。

原始碼分析

CharArrayWriter

package java.io;

import java.util.Arrays;

public class CharArrayWriter extends Writer {
    // 字元陣列緩衝
    protected char buf[];

    // 下一個字元的寫入位置
    protected int count;

    // 建構函式：預設緩衝區大小是32
    public CharArrayWriter() {
        this(32);
    }

    // 建構函式：指定緩衝區大小是initialSize
    public CharArrayWriter(int initialSize) {
        if (initialSize < 0) {
            throw new IllegalArgumentException("Negative initial size: "
                                               + initialSize);
        }
        buf = new char[initialSize];
    }

    // 寫入一個字元c到CharArrayWriter中
    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;
        }
    }

    // 寫入字元陣列c到CharArrayWriter中。off是“字元陣列b中的起始寫入位置”，len是寫入的長度
    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;
        }
    }

    // 寫入字串str到CharArrayWriter中。off是“字串的起始寫入位置”，len是寫入的長度
    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;
        }
    }

    // 將CharArrayWriter寫入到“Writer物件out”中
    public void writeTo(Writer out) throws IOException {
        synchronized (lock) {
            out.write(buf, 0, count);
        }
    }

    // 將csq寫入到CharArrayWriter中
    // 注意：該函式返回CharArrayWriter物件
    public CharArrayWriter append(CharSequence csq) {
        String s = (csq == null ? "null" : csq.toString());
        write(s, 0, s.length());
        return this;
    }

    // 將csq從start開始(包括)到end結束(不包括)的資料，寫入到CharArrayWriter中。
    // 注意：該函式返回CharArrayWriter物件！ 
    public CharArrayWriter append(CharSequence csq, int start, int end) {
        String s = (csq == null ? "null" : csq).subSequence(start, end).toString();
        write(s, 0, s.length());
        return this;
    }

    // 將字元c追加到CharArrayWriter中！
    // 注意：它與write(int c)的區別。append(char c)會返回CharArrayWriter物件。
    public CharArrayWriter append(char c) {
        write(c);
        return this;
    }

    // 重置
    public void reset() {
        count = 0;
    }

    // 將CharArrayWriter的全部資料對應的char[]返回
    public char toCharArray()[] {
        synchronized (lock) {
            return Arrays.copyOf(buf, count);
        }
    }

    // 返回CharArrayWriter的大小
    public int size() {
        return count;
    }

    public String toString() {
        synchronized (lock) {
            return new String(buf, 0, count);
        }
    }

    public void flush() { }

    public void close() { }
}
 

CharArrayWriter實際上是將資料寫入“字元陣列”中

總結：

1，通過CharArrayWriter（）建立的CharArrayWriter對應的字元陣列大小是32

2，通過CharArrayWriter(int size)建立的CharArrayWriter對應字元陣列大小是size

3，writer(int oneChar)的作用是將int型別的oneChar換成char型別，然後寫入到CharArrayWriter中

4，write(char[] buffer, int offset ,intcount)是將字元陣列buffer寫入到輸出流中，offset是從buffer中讀取資料的起始便宜位置，len是讀取的長度，

5，write(String str, int offset ,intcount)作用是將字串寫入輸出流中，offset是讀取資料的起始位置，count是讀取的長度

6，append（char c）的作用是將char型別的c寫入到CharArrayWriter中，他們的區別是append（char c）會返回一個CharArrayWriter物件，但是write(int c )返回void

7,append(CharSequence csq, int start, int end)的作用將csq從start開始(包括)到end結束(不包括)的資料，寫入到CharArrayWriter中。

8,append(CharSequence csq)的作用將csq寫入到CharArrayWriter中。

9,writeTo(OutputStream out) 將該“字元陣列輸出流”的資料全部寫入到“輸出流out”中。

示例程式碼

package io;
import java.io.CharArrayReader;
import java.io.CharArrayWriter;
import java.io.IOException;


/**
 * CharArrayWriter 測試程式
 *
 * @author skywang
 */
public class CharArrayWriterTest {

    private static final int LEN = 5;
    // 對應英文字母“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) {

        tesCharArrayWriter() ;
    }

    /**
     * CharArrayWriter的API測試函式
     */
    private static void tesCharArrayWriter() {
        try {
            // 建立CharArrayWriter字元流
            CharArrayWriter caw = new CharArrayWriter();

            // 寫入“A”個字元
            caw.write('A');
            // 寫入字串“BC”個字元
            caw.write("BC");
            //System.out.printf("caw=%s\n", caw);
            // 將ArrayLetters陣列中從“3”開始的後5個字元(defgh)寫入到caw中。
            caw.write(ArrayLetters, 3, 5);
            //System.out.printf("caw=%s\n", caw);

            // (01) 寫入字元0
            // (02) 然後接著寫入“123456789”
            // (03) 再接著寫入ArrayLetters中第8-12個字元(ijkl)
            caw.append('0').append("123456789").append(String.valueOf(ArrayLetters), 8, 12);

            System.out.printf("caw=%s\n", caw);

            // 計算長度
            int size = caw.size();
            System.out.printf("size=%s\n", size);

            // 轉換成byte[]陣列
            char[] buf = caw.toCharArray();
            System.out.printf("buf=%s\n", String.valueOf(buf));

            // 將caw寫入到另一個輸出流中
            CharArrayWriter caw2 = new CharArrayWriter();
            caw.writeTo(caw2);
            System.out.printf("caw2=%s\n", caw2);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

執行結果：

caw=ABCdefgh0123456789ijkl
size=22
buf=ABCdefgh0123456789ijkl
caw2=ABCdefgh0123456789ijkl

原文：http://www.cnblogs.com/skywang12345/p/io_19.html