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

// 构造函数BufferedWriter(Writer out) BufferedWriter(Writer out, int sz) void  close()               // 关闭此流，但要先刷新它。void  flush()               // 刷新该流的缓冲。void  newLine()              // 写入一个行分隔符。void  write(char[] cbuf, int off, int len) // 写入字符数组的某一部分。void  write(int c)             // 写入单个字符。void  write(String s, int off, int len)  // 写入字符串的某一部分。 

 package java.io;  public class BufferedWriter extends Writer {    // 输出流对象    private Writer out;    // 保存“缓冲输出流”数据的字符数组    private char cb[];   // nChars 是cb缓冲区中字符的总的个数   // nextChar 是下一个要读取的字符在cb缓冲区中的位置   private int nChars, nextChar;   // 默认字符缓冲区大小   private static int defaultCharBufferSize = ;   // 行分割符   private String lineSeparator;   // 构造函数，传入“Writer对象”，默认缓冲区大小是k   public BufferedWriter(Writer out) {     this(out, defaultCharBufferSize);   }   // 构造函数，传入“Writer对象”，指定缓冲区大小是sz   public BufferedWriter(Writer out, int sz) {     super(out);    if (sz <= 0)       throw new IllegalArgumentException("Buffer size <= ");     this.out = out;     cb = new char[sz];     nChars = sz;     nextChar = 0;     lineSeparator = java.security.AccessController.doPrivileged(       new sun.security.action.GetPropertyAction("line.separator"));   }   // 确保“BufferedWriter”是打开状态   private void ensureOpen() throws IOException {     if (out == null)       throw new IOException("Stream closed");   }   // 对缓冲区执行flush()操作，将缓冲区的数据写入到Writer中   void flushBuffer() throws IOException {     synchronized (lock) {       ensureOpen();      if (nextChar == 0)         return;       out.write(cb, 0, nextChar);       nextChar = 0;     }   }   // 将c写入到缓冲区中。先将c转换为char，然后将其写入到缓冲区。   public void write(int c) throws IOException {     synchronized (lock) {       ensureOpen();       // 若缓冲区满了，则清空缓冲，将缓冲数据写入到输出流中。       if (nextChar >= nChars)         flushBuffer();       cb[nextChar++] = (char) c;     }   }   // 返回a，b中较小的数   private int min(int a, int b) {     if (a < b) return a;     return b;   }   // 将字符数组cbuf写入到缓冲中，从cbuf的off位置开始写入，写入长度是len。   public void write(char cbuf[], int off, int len) throws IOException {     synchronized (lock) {       ensureOpen();       if ((off < 0) || (off > cbuf.length) || (len < 0) ||         ((off + len) > cbuf.length) || ((off + len) < 0)) {         throw new IndexOutOfBoundsException();       } else if (len == 0) {         return;       }       if (len >= nChars) {         /* If the request length exceeds the size of the output buffer,           flush the buffer and then write the data directly. In this           way buffered streams will cascade harmlessly. */         flushBuffer();         out.write(cbuf, off, len);         return;       }       int b = off, t = off + len;       while (b < t) {         int d = min(nChars - nextChar, t - b);         System.arraycopy(cbuf, b, cb, nextChar, d);         b += d;         nextChar += d;         if (nextChar >= nChars)           flushBuffer();       }     }   }   // 将字符串s写入到缓冲中，从s的off位置开始写入，写入长度是len。   public void write(String s, int off, int len) throws IOException {     synchronized (lock) {       ensureOpen();       int b = off, t = off + len;       while (b < t) {         int d = min(nChars - nextChar, t - b);         s.getChars(b, b + d, cb, nextChar);         b += d;         nextChar += d;         if (nextChar >= nChars)           flushBuffer();       }     }   }   // 将换行符写入到缓冲中   public void newLine() throws IOException {     write(lineSeparator);   }   // 清空缓冲区数据   public void flush() throws IOException {     synchronized (lock) {       flushBuffer();       out.flush();     }   }   public void close() throws IOException {     synchronized (lock) {       if (out == null) {         return;       }       try {         flushBuffer();       } finally {         out.close();         out = null;         cb = null;       }     }   } }

import java.io.BufferedWriter; import java.io.File; import java.io.OutputStream; import java.io.FileWriter; import java.io.IOException; import java.io.FileNotFoundException; import java.lang.SecurityException; import java.util.Scanner; /** * BufferedWriter 测试程序 * *  */ public class BufferedWriterTest {  private static final int LEN = 5;   // 对应英文字母“abcdefghijklmnopqrstuvwxyz”   //private static final char[] ArrayLetters = "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) {     testBufferedWriter() ;   }   /**   * BufferedWriter的API测试函数   */   private static void testBufferedWriter() {     // 创建“文件输出流”对应的BufferedWriter     // 它对应缓冲区的大小是16，即缓冲区的数据>=16时，会自动将缓冲区的内容写入到输出流。     try {       File file = new File("bufferwriter.txt");       BufferedWriter out =          new BufferedWriter(            new FileWriter(file));      // 将ArrayLetters数组的前10个字符写入到输出流中      out.write(ArrayLetters, 0, 10);       // 将“换行符/n”写入到输出流中       out.write('/n');       out.flush();       //readUserInput() ;       out.close();    } catch (FileNotFoundException e) {      e.printStackTrace();    } catch (SecurityException e) {      e.printStackTrace();    } catch (IOException e) {      e.printStackTrace();    }   }   /**   * 读取用户输入   */   private static void readUserInput() {     System.out.println("please input a text:");     Scanner reader=new Scanner(System.in);     // 等待一个输入     String str = reader.next();     System.out.printf("the input is : %s/n", str);   } }