2011-09-01--RandomAccessFile 随机读取文件

/*
 * 2011 09 01 题目要求是实现随机写文件中10个double数据，然后格式化输出
 * 简单设计了一下，使用了 java.text.DecimalFormat中的pattern方法来
 * 构建格式，其实跟regex的写法类似，不过要简单一点。
 * Younger.Shen  申延刚
 * younger.x.shen@gmail.com
 * blog.youkuaiyun.com/hack2me
 
 
0
一位数字，这一位缺失显示为0。用来补零

#
一位数字, 这一位缺失就不显示

.
小数点，不用多说了吧

,
千位分隔符

E
科学计数法

%
百分比
*/

package com.youngershen.io.test;


import java.io.*;
import java.util.*;
import java.text.*;

public class RandomAccessFileDemo {

	private RandomAccessFile f = null;
	private ArrayList<Double> d = new ArrayList<Double>();
	private File file = null;

	
	
	public RandomAccessFileDemo(String name) {
		
		file = new File(name);
	
		
		try {
			
			f = new  RandomAccessFile(file,"rw");
			
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		operate();
		readOut();
		
	}
	
	public void operate(){
		
		for(int i=0;i<10;i++){
			
			try {
				
				f.writeDouble(Math.random()*10);
		
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			
		}
		try {
			
			f.close();
	
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
	
	
	public static void patternPrint(String pattern, double x) {

		DecimalFormat df = new DecimalFormat(pattern);

		System.out.println(df.format(x));

		
	}
	public void readOut(){
		
		try {
			
			f = new RandomAccessFile(file,"r") ;
			
		} catch (FileNotFoundException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}
		
	
		
		for(int i=0;i<10;i++){
			
			try {
				
				f.seek(i*8);
				
				d.add(f.readDouble());
			
				
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		
		for(int i=0;i<10;i++){
			
		
			patternPrint("#.###" , d.get(i));
			
		}
		
		try{
			
			f.close();
			
		}catch(IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
	public static void main(String[] args){
		
		new RandomAccessFileDemo("./sss.txt");
		System.out.println("hello");
		
	}
}