ruby写的生日问题

chenwar — Wed, 02 Jul 2008 16:59:26 +0800

作者: chenwar 链接：http://chenwar.javaeye.com/blog/210704 发表时间: 2008年07月02日

声明：本文系JavaEye网站发布的原创博客文章，未经作者书面许可，严禁任何网站转载本文，否则必将追究法律责任！

才学ruby三天，写了个生日概率问题，和理论结果不同，暂时不知道错在何处？
问题：n个人中有两个人生日相同的概率是多少？
#生日问题
arr = Array.new
a=0
b=1
person_num = 20 # 人数
loopnum =0
num=0 #记录person_num内生日相同的次数
sum=50000 #循环次数
while loopnum while a
arr[arr.size] = rand(365) #365内的随机数

for i in 0..arr.size

if arr[i]==arr.last and i!=(arr.size-1)
# if i
num+=1

#end
b = 0
break
end
end
a+=1
end #end of a
loopnum+=1
a=0
arr.clear #清空数组
b=1
end #end of loopnum
puts person_num.to_s + "个人生日相同的概率是"+(Float(num*100)/Float(sum)).to_s+"%"
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学习一种缓存方法(转)

chenwar — Wed, 21 May 2008 11:26:04 +0800

作者: chenwar 链接：http://chenwar.javaeye.com/blog/195162 发表时间: 2008年05月21日

声明：本文系JavaEye网站发布的原创博客文章，未经作者书面许可，严禁任何网站转载本文，否则必将追究法律责任！

CacheManager类
使用一个HashMap来缓存从数据库中查询出的Object,并提供获取，存放，清除的方法
//---------------------------------------------------------
// Application: Company Applcation
// Author : Cao guangxin
// File : CacheManager.java
//
// Copyright 2006 RelationInfo Software
// Writed at Wed Apr 12 08:58:55 CST 2006
// writed by Eclipse SDK
// Visit http://www.37signals.cn
//---------------------------------------------------------

package net.cn37signals.company.util;

import java.util.Comparator;
import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.TreeMap;

class CostComparator implements Comparator {
public int compare(Object o1, Object o2) {
return ((Double) o1).compareTo((Double) o2);
}

public boolean equals(Object o) {
return super.equals(o);
}
}

public class CacheManager {
//三种清除cache时的排序策略
public static int LRU = 0;

public static int LFU = 1;

public static int MIX = 2;

//使用一个HashMap来存储Object
private HashMap cacheHashMap = new HashMap();

private int CACHE_CAPACITY = 100;

private int TRESHOLD = 90;

private int purgeAlgorithm;

private long hitCount = 0;

private long missCount = 0;

public CacheManager(int purgeAlgorithm, int cacheCapacity, int treshold) {
this.purgeAlgorithm = purgeAlgorithm;
CACHE_CAPACITY = cacheCapacity;
TRESHOLD = treshold;
}

public CacheManager(int purgeAlgorithm) {
this.purgeAlgorithm = purgeAlgorithm;
}

/**
*根据字符串identifier从cacheHashMap容器中获取cachedObject对象
*如果cacheHashMap中没有identifier键，或cachedObject已经过时，则返回null,
*同时missCount值加1
*否则获取对应的cachedObject对象，并使hitCount加1
*/
public synchronized Object getCache(String identifier) {
CachedObject cachedObject = (CachedObject) cacheHashMap.get(identifier);
Object obj = null;

if (cachedObject == null) {
missCount++;
} else if (cachedObject.isExpired()) {
cacheHashMap.remove(identifier);
missCount++;
} else {
cachedObject.incNumAccess();
cachedObject.setLastAccessTime(new Date());
hitCount++;
obj = cachedObject.getObject();
}
return obj;
}

public synchronized void invalidate(String identifier) {
cacheHashMap.remove(identifier);
}

public long getHitCount() {
return hitCount;
}

public long getMissCount() {
return missCount;
}

public long getCurrentCacheSize() {
return cacheHashMap.size();
}

public synchronized void putCache(Object object, String id,
int minutesToLive) {
CachedObject cachedObject = new CachedObject(object, id, minutesToLive);
if (cacheHashMap.size() == CACHE_CAPACITY) {
sweep();
}
cacheHashMap.put(id, cachedObject);
}

/**
*cacheHashMap容器的整理
*先将超时的cachedObject清除，
*当cachedObject数量大于TRESHOLD时，将访问频率小（次数小）的cachedObject清除
*/
public synchronized void sweep() {
TreeMap costTreeMap = new TreeMap(new CostComparator());
for (Iterator i = cacheHashMap.entrySet().iterator(); i.hasNext();) {
Map.Entry entry = (Map.Entry) i.next();
CachedObject cachedObject = (CachedObject) entry.getValue();
if (cachedObject.isExpired()) {
cacheHashMap.remove(entry.getKey());
} else {
double cost = 0.0;
switch (purgeAlgorithm) {
case 0:
cost = cachedObject.getLFUCost();
break;
case 1:
cost = cachedObject.getLRUCost();
break;
default:
cost = cachedObject.getMixCost();
}
costTreeMap.put(new Double(cost), entry.getKey());
}
}

// delete to treshold
for (int i = cacheHashMap.size(); i > TRESHOLD; i--) {
Object kk = costTreeMap.firstKey();
Object k = costTreeMap.get(kk);
cacheHashMap.remove(k);
costTreeMap.remove(kk);
}
}

public void clearCache() {
hitCount = 0;
missCount = 0;
cacheHashMap.clear();
}

/**
*将字符数组生成形如:"keys1/keys2/keys3"的字符串
*/
public static String createKey(String[] keys) {
StringBuffer newKey = new StringBuffer("");
for (int i = 0; i < keys.length; i++)
newKey.append(keys[i]).append("/");
return newKey.toString();
}
}

//==============================
DAOCacheManager类
持有一个静态的CacheManager类对象，提供对其的操作方法
业务方法都要通过他来使用cacheManager
//---------------------------------------------------------
// Application: Company Applcation
// Author : Cao guangxin
// File : DAOCacheManager.java
//
// Copyright 2006 RelationInfo Software
// Writed at Wed Apr 12 08:58:55 CST 2006
// writed by Eclipse SDK
// Visit http://www.37signals.cn
//---------------------------------------------------------

package net.cn37signals.company.dao;

import java.text.MessageFormat;

import net.cn37signals.company.util.CacheManager;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class DAOCacheManager {
private static Log log = LogFactory.getFactory().getInstance("DAOCacheManager");
//cacheManager是静态的，供多个线程公用
private static CacheManager cacheManager = new CacheManager(CacheManager.MIX);

/**
*从cache中获取对象
*/
public static Object getCache(String identifier) {
if (log.isInfoEnabled()) {
Object[] o = {new Long(cacheManager.getHitCount()), new Long(cacheManager.getMissCount())};
log.info(MessageFormat.format(" [DAOCacheManager] getCache: {0} hits, {1} misses", o));
}
return cacheManager.getCache(identifier);
}

/**
*将对象放入cache中
*/
public static void putCache(Object object, String id, int minutesToLive) {
if (log.isInfoEnabled()) {
log.info(" [DAOCacheManager] putCache");
}
cacheManager.putCache(object, id, minutesToLive);
}

public static void invalidate(String id) {
cacheManager.invalidate(id);
}

}
//=====================
CachedObject类
对要放入cache的对象进行包装
//---------------------------------------------------------
// Application: Company Applcation
// Author : Cao guangxin
// File : CachedObject.java
//
// Copyright 2006 RelationInfo Software
// Writed at Wed Apr 12 08:58:55 CST 2006
// writed by Eclipse SDK
// Visit http://www.37signals.cn
//---------------------------------------------------------

package net.cn37signals.company.util;

import java.util.Calendar;
import java.util.Date;
import java.util.List;

public class CachedObject {

public Object object = null;
private Date dateofExpiration = null;
private String identifier = null;
private Date lastAccessTime = new Date();
private long numAccess = 1;
private int size;

// +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

public CachedObject(Object obj, String id, int minutesToLive) {
this.object = obj;
this.identifier = id;

size = objectSize(obj);
lastAccessTime = new Date();
// minutesToLive of 0 means it lives on indefinitely.
if (minutesToLive != 0) {
Calendar cal = Calendar.getInstance();
cal.setTime(lastAccessTime);
cal.add(cal.MINUTE, minutesToLive);
dateofExpiration = cal.getTime();
}
}

public void setLastAccessTime(Date lastAccessTime) {
this.lastAccessTime = lastAccessTime;
}

public boolean isExpired() {
// Remember if the minutes to live is zero then it lives forever!
if (dateofExpiration != null && dateofExpiration.before(new Date())) {
return true;
}
return false;
}

public String getIdentifier() {
return identifier;
}

public Object getObject() {
return object;
}

public Date getDateofExpiration() {
return (this.dateofExpiration);
}

public Date getLastAccessTime() {
return (this.lastAccessTime);
}

public long getNumAccess() {
return (this.numAccess);
}

public long getSize() {
return (this.size);
}

public double getMixCost() {
long milis = new Date().getTime() - lastAccessTime.getTime();
if(milis == 0) {
milis = 1;
}
return (double)numAccess / (double)milis / (double)size;
}

public double getLRUCost() {
long milis = new Date().getTime() - lastAccessTime.getTime();
if(milis == 0) {
milis = 1;
}
return 1.0/(double)milis;
}

public double getLFUCost() {
return (double) numAccess;
}

public void incNumAccess() {
numAccess++;
}

public boolean equals(Object o2) {
try {
String key2 = ((CachedObject) o2).getIdentifier();
return identifier.equals(key2);
} catch (Exception e) {
return false;
}
}

private static int objectSize(Object o) {
try {
int size = ((List) o).size();
return size + 1;
} catch (Exception e) {
return 1;
}
}

}
//==============================
使用方法
public List list(int offset, int limit) throws SQLException {
String[] objKeys = {"Users", "list", String.valueOf(offset), String.valueOf(limit)};
String objKey = CacheManager.createKey(objKeys);
ArrayList list = (ArrayList) DAOCacheManager.getCache(objKey);
//如果cache的hashmap中有，直接取出，没有则从数据库中查询，并放入hashmap中
if (list != null)
return list;
//--
//从数据库中查询(略)
//--
//将查询结果放入cache
DAOCacheManager.putCache(list, objKey, 1);
return list;
}
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mysql中文问题

chenwar — Wed, 21 May 2008 10:11:45 +0800

作者: chenwar 链接：http://chenwar.javaeye.com/blog/195105 发表时间: 2008年05月21日

声明：本文系JavaEye网站发布的原创博客文章，未经作者书面许可，严禁任何网站转载本文，否则必将追究法律责任！

mysql-connector-java-3.1.12-bin.jar
jdk1.5.0_06

java内部使用unicode,mysql使用iso-8859-1
如果在程序中添加转换编码较为麻烦，我试图用以下方法

在C:\WINDOWS\my.ini文件中加入一句
default-character-set=gbk
“gbk”为小写

连接字符串改为：
connection = DriverManager.getConnection( "jdbc:mysql://localhost/test?user=root&password=&useUnicode=true&characterEncoding=GBK" );

在MySQL-Front工具中将所有表，字段的字符集都改为gb2312或gbk

.......

jsp页面输入中文，提交，成功！！--->吃饭
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