Android中完全退出当前应用系统

package com.jsmtr.www.Helper;

import java.util.LinkedList;
import java.util.List;

import android.app.Activity;
import android.app.Application;

public class ActivityManager extends Application {
    @SuppressWarnings("rawtypes")
    private List list = new LinkedList();
    private static ActivityManager instance;

    private ActivityManager () {
    }

    public synchronized static ActivityManager getInstance() {
        if (null == instance) {
            instance = new ActivityManager ();
        }
        return instance;
    }

    @SuppressWarnings("unchecked")
    public void addActivity(Activity activity) {
        list.add(activity);
    }

    public void exit() {
        try {
            for (int i = 0; i < list.size(); i++) {
                Activity activity = (Activity) list.get(i);
                if (activity != null)
                    activity.finish();
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            System.exit(0);
        }
    }

    public void onLowMemory() {
        super.onLowMemory();
        System.gc();
    }
}

ActivityManager.getInstance().addActivity(this);

ActivityManager.getInstance().exit();