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java io进修(十八) CharArrayWriter(字符数组输出流)

2017-11-02 08:00 星期四 所属: JAVA 教程 浏览:45

副标题#e#

CharArrayWriter 先容

CharArrayReader 用于写入数据符,它担任于Writer。操纵的数据是以字符为单元!

CharArrayWriter 函数列表

CharArrayWriter()
CharArrayWriter(int initialSize)
     
CharArrayWriter     append(CharSequence csq, int start, int end)
CharArrayWriter     append(char c)
CharArrayWriter     append(CharSequence csq)
void     close()
void     flush()
void     reset()
int     size()
char[]     toCharArray()
String     toString()
void     write(char[] buffer, int offset, int len)
void     write(int oneChar)
void     write(String str, int offset, int count)
void     writeTo(Writer out)

Writer和CharArrayWriter源码阐明

Writer是CharArrayWriter的父类,我们先看看Writer的源码,然后再学CharArrayWriter的源码。

1. Writer源码阐明(基于jdk1.7.40)

package java.io;
     
public abstract class Writer implements Appendable, Closeable, Flushable {
     
    private char[] writeBuffer;
     
    private final int writeBufferSize = 1024;
     
    protected Object lock;
     
    protected Writer() {
        this.lock = this;
    }
     
    protected Writer(Object lock) {
        if (lock == null) {
            throw new NullPointerException();
        }
        this.lock = lock;
    }
     
    public void write(int c) throws IOException {
        synchronized (lock) {
            if (writeBuffer == null){
                writeBuffer = new char[writeBufferSize];
            }
            writeBuffer[0] = (char) c;
            write(writeBuffer, 0, 1);
        }
    }
     
    public void write(char cbuf[]) throws IOException {
        write(cbuf, 0, cbuf.length);
    }
     
    abstract public void write(char cbuf[], int off, int len) throws IOException;
     
    public void write(String str) throws IOException {
        write(str, 0, str.length());
    }
     
    public void write(String str, int off, int len) throws IOException {
        synchronized (lock) {
            char cbuf[];
            if (len <= writeBufferSize) {
                if (writeBuffer == null) {
                    writeBuffer = new char[writeBufferSize];
                }
                cbuf = writeBuffer;
            } else {    // Don't permanently allocate very large buffers.
                cbuf = new char[len];
            }
            str.getChars(off, (off + len), cbuf, 0);
            write(cbuf, 0, len);
        }
    }
     
    public Writer append(CharSequence csq) throws IOException {
        if (csq == null)
            write("null");
        else
            write(csq.toString());
        return this;
    }
     
    public Writer append(CharSequence csq, int start, int end) throws IOException {
        CharSequence cs = (csq == null ? "null" : csq);
        write(cs.subSequence(start, end).toString());
        return this;
    }
     
    public Writer append(char c) throws IOException {
        write(c);
        return this;
    }
     
    abstract public void flush() throws IOException;
     
    abstract public void close() throws IOException;
}


#p#副标题#e#

2. CharArrayWriter 源码阐明(基于jdk1.7.40)

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;
     
    // 结构函数:默认缓冲区巨细是32
    public CharArrayWriter() {
        this(32);
    }
     
    // 结构函数:指定缓冲区巨细是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
	// 查察本栏目

说明:

CharArrayWriter实际上是将数据写入到“字符数组”中去。

(01) 通过CharArrayWriter()建设的CharArrayWriter对应的字符数组巨细是32。

(02) 通过CharArrayWriter(int size) 建设的CharArrayWriter对应的字符数组巨细是size。

(03) write(int oneChar)的浸染将int范例的oneChar换成char范例,然后写入到CharArrayWriter中。

(04) write(char[] buffer, int offset, int len) 是将字符数组buffer写入到输出流中,offset是从buffer中读取数据的起始偏移位置,len是读取的长度。

(05) write(String str, int offset, int count) 是将字符串str写入到输出流中,offset是从str中读取数据的起始位置,count是读取的长度。

(06) append(char c)的浸染将char范例的c写入到CharArrayWriter中,然后返回CharArrayWriter工具。

留意:append(char c)与write(int c)都是将单个字符写入到CharArrayWriter中。它们的区别是,append(char c)会返回CharArrayWriter工具,可是write(int c)返回void。

(07) append(CharSequence csq, int start, int end)的浸染将csq从start开始(包罗)到end竣事(不包罗)的数据,写入到CharArrayWriter中。

留意:该函数返回CharArrayWriter工具!

(08) append(CharSequence csq)的浸染将csq写入到CharArrayWriter中。

留意:该函数返回CharArrayWriter工具!

(09) 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

#p#分页标题#e#

关于CharArrayWriter中API的具体用法,参考示例代码(CharArrayWriterTest.java):

import java.io.CharArrayReader;
import java.io.CharArrayWriter;
import java.io.IOException;
     
     
/**
 * CharArrayWriter 测试措施
 *
 * @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 {
            // 建设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);
     
            // 计较长度
            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();
        }
    }
}

运行功效:

caw=ABCdefgh0123456789ijkl

size=22

buf=ABCdefgh0123456789ijkl

caw2=ABCdefgh0123456789ijkl

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

 

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