date and time in Android

本文总结Android中有关时间日期的用法

1、用示例介绍Date、DateFormat、Calendar的用法

Date date = new Date();//current time,values come from System.currentTimeMillis
Log.println(Log.INFO, TAG, "Date:"+date.getYear()+"-"+date.getMonth()+"-"+date.getDay()
+"-"+date.getHours()+"-"+date.getMinutes()+"-"+date.getSeconds());
//abstract class,format a date for display to a human
DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH-mm-ss E");
String dateTime = dateFormat.format(date);
Log.println(Log.INFO, TAG, dateTime);
//default Locale,default TimeZone,current date and time
//break down a date if you need to extract fields
Calendar calendar = Calendar.getInstance();//abstract class
Log.println(Log.INFO, TAG, calendar.get(Calendar.YEAR)+"-"+(calendar.get(Calendar.MONTH)+1)
+"-"+calendar.get(Calendar.DAY_OF_MONTH)+"-"+calendar.get(Calendar.HOUR)
+"-"+calendar.get(Calendar.MINUTE)+"-"+calendar.get(Calendar.SECOND));

2、System、SystemClock、Thread对时间的支持

用一个示例演示用法，any question可查看代码中的注释。

public class MainActivity extends Activity {
private static final String TAG = MainActivity.class.getSimpleName();
long start = SystemClock.elapsedRealtime();
long start_up = SystemClock.uptimeMillis();
/**milliseconds running in the current thread*/
long start_app = SystemClock.currentThreadTimeMillis();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//add all top-level views to screen
getWindow().setContentView(R.layout.activity_main);
findViewById(R.id.btn).setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
new Thread(){
public void run() {
super.run();
//regardless of the system's time zone
//called "Unix time" or "epoch time"
//depends on system time
long time1 = System.currentTimeMillis();//since January 1, 1970 00:00:00.0 UTC
Log.println(Log.INFO, TAG, "System.currentTimeMillis:"+time1+"ms");
//Equivalent to Linux's CLOCK_MONOTONIC
//only be used to measure a duration by comparing it against another timestamp on the same device
long time2 = System.nanoTime();//since booted
Log.println(Log.INFO, TAG, "System.nanoTime:"+time2+"ns");
SystemClock.sleep(500);
long time3 = SystemClock.elapsedRealtimeNanos();//17
try {
//The precision is not guaranteed, the Thread may sleep more or less than requested
Thread.sleep(500, 500000);
} catch (InterruptedException e) {
e.printStackTrace();
}
Log.println(Log.INFO, TAG, "Thread.sleep:"+(SystemClock.elapsedRealtimeNanos()-time3)+"ns");
};
}.start();
}
});
}
@Override
protected void onResume() {
Log.println(Log.INFO, TAG, "onResume");
Log.println(Log.INFO, TAG, "sleep:"+(SystemClock.elapsedRealtime()-start)+"ms");
Log.println(Log.INFO, TAG, "non-sleep:"+(SystemClock.uptimeMillis()-start_up)+"ms");
super.onResume();
}
@Override
protected void onPause() {
Log.println(Log.INFO, TAG, "onPause");
start = SystemClock.elapsedRealtime();
start_up = SystemClock.uptimeMillis();
start_app = SystemClock.currentThreadTimeMillis();
Log.println(Log.INFO, TAG, start+"ms"+"-"+start_up+"ms"+"-"+start_app+"ms");//what's the difference?
Log.println(Log.INFO, TAG, "start-start_up="+(start-start_up));//deep sleep time
super.onPause();
}
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
xmlns:android="http://schemas.android.com/apk/res/android">
<Button
android:id="@+id/btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="sleep"/>
</LinearLayout>

下面异常由Thread.sleep(long,int)抛出



3、详细介绍DateFormat的用法

DateFormat使用了简单工厂模式，其中工厂角色与抽象产品角色合并，具体产品角色只有SimpleDateFormat

//均为SimpleDateFormat实例
DateFormat[] dateFormats = {DateFormat.getDateInstance(),
DateFormat.getDateTimeInstance(),
DateFormat.getTimeInstance()};
for(DateFormat df:dateFormats){
Log.d(TAG, df.format(new Date(0L)));
df.setTimeZone(TimeZone.getTimeZone("UTC"));
Log.d(TAG, df.format(new Date(0L)));
}
Locale[] locales = DateFormat.getAvailableLocales();
//locale.toLanguageTag() API 21
for(Locale locale:locales){
Log.d(TAG, "Locale:"+locale.toString());
}
String[] ids = TimeZone.getAvailableIDs();
for(String id:ids){
Log.d(TAG, "id:"+id);
}
//SHORT, MEDIUM, LONG, FULL, or DEFAULT
Log.d(TAG, DateFormat.getDateInstance(DateFormat.SHORT, Locale.CHINA).format(new Date(0L)));
Log.d(TAG, DateFormat.getDateInstance(DateFormat.MEDIUM, Locale.UK).format(new Date(0L)));//DEFAULT 2
Log.d(TAG, DateFormat.getDateInstance(DateFormat.LONG, Locale.US).format(new Date(0L)));
Log.d(TAG, DateFormat.getDateInstance(DateFormat.FULL, Locale.TAIWAN).format(new Date(0L)));

toLanguageTag方法在21引入，在低于21的设备会报如下异常