设计模式4——装饰模式(前)

设计模式4——装饰模式

 

★ 场景和问题

在不对原有对象类进行修改的基础上，如何给一个或多个已有的类对象提供增强额外的功能?

★ 引例

写一个MyBufferedReader类，使它能够对字符流(如FileReader、InputStreamReader和PipedReader等)进行功能增强：

(1) 提供带缓冲的myRead()方法，对原有的read()方法进行增速；

(2)提供一个能够每次读取一行字符的myReadLine()方法。

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;

import org.junit.Test;

public class TestMyBufferedreader {
 
 @Test
 public void jdk_testRead() throws IOException {
  FileReader r = new FileReader("a.txt");
  BufferedReader br = new BufferedReader( r );
  int ch=0;
  while( (ch=br.read())!=-1 ){
   System.out.print((char)ch);
  }
  br.close();
 }
 @Test
 public void my_testRead() throws IOException {
  InputStreamReader r = new InputStreamReader(new FileInputStream("a.txt"));
  MyBufferedReader br = new MyBufferedReader( r );
  int ch=0;
  while( (ch=br.myRead())!=-1 ){
   System.out.print((char)ch);
  }
  br.close();
 }
 
 
    /////
 @Test
 public void jdk_testReadLine() throws IOException {
  FileReader r = new FileReader("a.txt");
  BufferedReader br = new BufferedReader( r );
  String line = null;
  while( (line =br.readLine())!=null ){
   System.out.println(line);
  }
  br.close();
 }
 
 @Test
 public void my_testReadLine() throws IOException {
  InputStreamReader r = new InputStreamReader(new FileInputStream("a.txt"));
  MyBufferedReader br = new MyBufferedReader( r );
  String line = null;
  while( (line =br.myReadLine())!=null ){
   System.out.println(line);
  }
  br.close();
 }

}

import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;

public class MyBufferedReader extends Reader {//※※3※
 private Reader r;//※※1※
 private char[]cbuf = new char[1024];
 private int count=0;//记录缓冲区中字符的个数 100
 private int pos=0;
 public MyBufferedReader(Reader r){//※※2※
  this.r = r;
 }
 
 //功能增强1
 public int myRead() throws IOException{
  if(count<=0){
   count = r.read(cbuf);//50
   pos=0;
  }
  if(count==-1){
   return -1;
  }
  count--;//每读一次，缓冲区中的还剩的字符数减1
  char ch = cbuf[pos];//本次读的字符
  pos++;
  return ch;
 }

 public void close() throws IOException {
  r.close();
 }
 
 //换行:  linux--\n    window--\r\n
 public String myReadLine() throws IOException{
  StringBuffer sb = new StringBuffer();
  int ch=0;
  while( (ch=myRead())!=-1 ){
   if(ch=='\r'){
    continue;
   }
   if(ch=='\n'){
    return sb.toString();
   }
   sb.append( (char)ch );//字符连接  str = str+(char)ch;
  }
  if(sb.length()!=0){//文件的最后一行是没有换行符的
   return sb.toString();
  }
  return null;
 }

 @Override
 public int read(char[] cbuf, int off, int len) throws IOException {
  return r.read(cbuf, off, len);
 }

}