CharArrayWriter介绍
用于写入字符数据，继承于writer，操作的是单位为字符。
源码分析
CharArrayWriter
package java.io;
import java.util.Arrays;
public class CharArrayWriter extends Writer {
// 字符数组缓冲
protected char buf[];
// 下一个字符的写入位置
protected int count;
// 构造函数：默认缓冲区大小是32
public CharArrayWriter() {
this(32);
}
// 构造函数：指定缓冲区大小是initialSize
public CharArrayWriter(int initialSize) {
if (initialSize < 0) {
throw new IllegalArgumentException("Negative initial size: "
+ initialSize);
}
buf = new char[initialSize];
}
// 写入一个字符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;
}
}
// 写入字符数组c到CharArrayWriter中。off是“字符数组b中的起始写入位置”，len是写入的长度
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;
}
}
// 写入字符串str到CharArrayWriter中。off是“字符串的起始写入位置”，len是写入的长度
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;
}
}
// 将CharArrayWriter写入到“Writer对象out”中
public void writeTo(Writer out) throws IOException {
synchronized (lock) {
out.write(buf, 0, count);
}
}
// 将csq写入到CharArrayWriter中
// 注意：该函数返回CharArrayWriter对象
public CharArrayWriter append(CharSequence csq) {
String s = (csq == null ? "null" : csq.toString());
write(s, 0, s.length());
return this;
}
// 将csq从start开始(包括)到end结束(不包括)的数据，写入到CharArrayWriter中。
// 注意：该函数返回CharArrayWriter对象！
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;
}
// 将字符c追加到CharArrayWriter中！
// 注意：它与write(int c)的区别。append(char c)会返回CharArrayWriter对象。
public CharArrayWriter append(char c) {
write(c);
return this;
}
// 重置
public void reset() {
count = 0;
}
// 将CharArrayWriter的全部数据对应的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实际上是将数据写入“字符数组”中
总结：
1，通过CharArrayWriter（）创建的CharArrayWriter对应的字符数组大小是32
2，通过CharArrayWriter(int size)创建的CharArrayWriter对应字符数组大小是size
3，writer(int oneChar)的作用是将int类型的oneChar换成char类型，然后写入到CharArrayWriter中
4，write(char[] buffer, int offset ,intcount)是将字符数组buffer写入到输出流中，offset是从buffer中读取数据的起始便宜位置，len是读取的长度，
5，write(String str, int offset ,intcount)作用是将字符串写入输出流中，offset是读取数据的起始位置，count是读取的长度
6，append（char c）的作用是将char类型的c写入到CharArrayWriter中，他们的区别是append（char c）会返回一个CharArrayWriter对象，但是write(int c )返回void
7,append(CharSequence csq, int start, int end)的作用将csq从start开始(包括)到end结束(不包括)的数据，写入到CharArrayWriter中。
8,append(CharSequence csq)的作用将csq写入到CharArrayWriter中。
9,writeTo(OutputStream out) 将该“字符数组输出流”的数据全部写入到“输出流out”中。
示例代码
package io;
import java.io.CharArrayReader;
import java.io.CharArrayWriter;
import java.io.IOException;
/**
* CharArrayWriter 测试程序
*
* @author skywang
*/
public class CharArrayWriterTest {
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) {
tesCharArrayWriter() ;
}
/**
* CharArrayWriter的API测试函数
*/
private static void tesCharArrayWriter() {
try {
// 创建CharArrayWriter字符流
CharArrayWriter caw = new CharArrayWriter();
// 写入“A”个字符
caw.write('A');
// 写入字符串“BC”个字符
caw.write("BC");
//System.out.printf("caw=%s\n", caw);
// 将ArrayLetters数组中从“3”开始的后5个字符(defgh)写入到caw中。
caw.write(ArrayLetters, 3, 5);
//System.out.printf("caw=%s\n", caw);
// (01) 写入字符0
// (02) 然后接着写入“123456789”
// (03) 再接着写入ArrayLetters中第8-12个字符(ijkl)
caw.append('0').append("123456789").append(String.valueOf(ArrayLetters), 8, 12);
System.out.printf("caw=%s\n", caw);
// 计算长度
int size = caw.size();
System.out.printf("size=%s\n", size);
// 转换成byte[]数组
char[] buf = caw.toCharArray();
System.out.printf("buf=%s\n", String.valueOf(buf));
// 将caw写入到另一个输出流中
CharArrayWriter caw2 = new CharArrayWriter();
caw.writeTo(caw2);
System.out.printf("caw2=%s\n", caw2);
} catch (IOException e) {
e.printStackTrace();
}
}
}运行结果：
caw=ABCdefgh0123456789ijkl
size=22
buf=ABCdefgh0123456789ijkl
caw2=ABCdefgh0123456789ijkl