SimpleDateFormat format = new SimpleDateFormat("dd/MM/yyyy");
Calendar c = Calendar.getInstance();
Date date = Calendar.getInstance().getTime();
String sDate = format.format(date);//31-12-9999
int mYear = c.get(Calendar.YEAR);//9999
int mMonth = c.get(Calendar.MONTH);
mMonth = mMonth + 1;//12
int hrs = c.get(Calendar.HOUR_OF_DAY);//24
int min = c.get(Calendar.MINUTE);//59
String AMPM;
if (c.get(Calendar.AM_PM) == 0) {
    AMPM = "AM";
} else {
    AMPM = "PM";
}

从如何获得完整的日期与正确的格式?：

请使用

android.text.format.DateFormat.getDateFormat(Context context)
android.text.format.DateFormat.getTimeFormat(Context context)

获得当前用户设置意义上的有效时间和日期格式(例如12/24时间格式)。

import android.text.format.DateFormat;

private void some() {
    final Calendar t = Calendar.getInstance();
    textView.setText(DateFormat.getTimeFormat(this/*Context*/).format(t.getTime()));
}

实际上，最好使用TextClock小部件。它为您处理所有的复杂性，并将尊重用户的12/24小时的偏好。 http://developer.android.com/reference/android/widget/TextClock.html

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);
    Thread myThread = null;

    Runnable runnable = new CountDownRunner();
    myThread= new Thread(runnable);   
    myThread.start();

}

public void doWork() {
    runOnUiThread(new Runnable() {
        public void run() {
            try{
                TextView txtCurrentTime= (TextView)findViewById(R.id.lbltime);
                    Date dt = new Date();
                    int hours = dt.getHours();
                    int minutes = dt.getMinutes();
                    int seconds = dt.getSeconds();
                    String curTime = hours + ":" + minutes + ":" + seconds;
                    txtCurrentTime.setText(curTime);
            }catch (Exception e) {}
        }
    });
}


class CountDownRunner implements Runnable{
    // @Override
    public void run() {
            while(!Thread.currentThread().isInterrupted()){
                try {
                doWork();
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                }catch(Exception e){
                }
            }
    }
}

String currentDateandTime = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
Toast.makeText(getApplicationContext(), currentDateandTime, Toast.LENGTH_SHORT).show();

显示时间的明显选择是类比时钟视图(AnalogClock View)和数字时钟视图(DigitalClock View)。

例如，如下布局:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" 
    android:orientation="vertical">

    <AnalogClock
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content"/>

    <DigitalClock 
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        android:gravity="center" 
        android:textSize="20sp"/>
</LinearLayout>

看起来是这样的: