Java 学习 UUID 与 时间格式化 为了生成唯一身份识别码

String uuid1 = UUID.randomUUID().toString();
Log.e(TAG, "uuid1 默认的uuid: "+uuid1);
String uuid2 = UUID.randomUUID().toString().replace("-","");//格式化UUID将“-”去掉
Log.e(TAG, "uuid2 将“-”去掉: "+uuid2);
String uuid3 = UUID.randomUUID().toString().replace("-",".");//格式UUID将“-”格式成“.”
Log.e(TAG, "uuid3 将“-”格式成“.”: "+uuid3);
String uuid4 = UUID.randomUUID().toString().concat(".apk");//格式UUID,在UUID的结尾添加.apk
Log.e(TAG, "uuid4 结尾添加.apk: "+uuid4);
String uuid5 = UUID.randomUUID().toString().replaceAll("\\d","");//替换所有,参数1为要替换的字符正则表达式,参数2为替换字符；
Log.e(TAG, "uuid5 去掉所有数字: "+uuid5);

UUID newuuid = UUID.fromString(uuid1);//将String类型 转成 UUID
UUID u1 = UUID.randomUUID();
UUID u2 = UUID.randomUUID();
int values = u1.compareTo(u2);  // -1=小于  0=等于  1=大于
Log.e(TAG, "u1 对比 u2: "+values);//注意UUID对比 不会根据生成时间就比较大，它只是简单的比较字符大小

结果：

08-16 14:54:27.134 18951-18951/yt.yunwatch E/DemoActivity: uuid1 默认的uuid: 02f33031-dbb6-465f-9645-11388b3f08c6
08-16 14:54:27.135 18951-18951/yt.yunwatch E/DemoActivity: uuid2 将“-”去掉: f7b60f9a76954939afd773c158527b99
08-16 14:54:27.135 18951-18951/yt.yunwatch E/DemoActivity: uuid3 将“-”格式成“.”: 2c5c2843.a122.465b.bb23.963221fb32ed
08-16 14:54:27.136 18951-18951/yt.yunwatch E/DemoActivity: uuid4 结尾添加.apk: f466f910-0ed9-4a26-8532-bee14272136f.apk
08-16 14:54:27.137 18951-18951/yt.yunwatch E/DemoActivity: uuid5 去掉所有数字: fdb-ca-d-b-cfaee
08-16 14:54:27.138 18951-18951/yt.yunwatch E/DemoActivity: u1 对比 u2: -1

Java格式化时间到毫秒：

SimpleDateFormat formatter = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss:SSS");

String formatStr =formatter.format(new Date();

附录：

java格式化字母表

Symbol	Meaning	Presentation	Example
G	era designator	Text	AD
y	year	Number	2009
M	month in year	Text & Number	July & 07
d	day in month	Number	10
h	hour in am/pm (1-12)	Number	12
H	hour in day (0-23)	Number	0
m	minute in hour	Number	30
s	second in minute	Number	55
S	millisecond	Number	978
E	day in week	Text	Tuesday
D	day in year	Number	189
F	day of week in month	Number	2 (2nd Wed in July)
w	week in year	Number	27
W	week in month	Number	2
a	am/pm marker	Text	PM
k	hour in day (1-24)	Number	24
K	hour in am/pm (0-11)	Number	0
z	time zone	Text	Pacific Standard Time
'	escape for text	Delimiter	(none)
'	single quote	Literal	'