一些Java的实用代码

1.生成不重复随机数

long now = System.currentTimeMillis();
now = now << 16;
System.out.println(now | new Random().nextInt(0xffff));

2.正则表达式替换字符串

Pattern pattern = Pattern.compile("cat");
Matcher matcher = pattern.matcher("one cat two cats in the cat's yard");
StringBuffer buff = new StringBuffer();
while(matcher.find()){
	matcher.appendReplacement(buff, "dog");
}
matcher.appendTail(buff);