Android design mode-perfect Singleton Mode

Android design mode-perfect Singleton Mode

Android perfect Singleton mode:

The previous Singleton mode was not fully considered;

This problem was obtained during the interview;

Even with such a problem, we can see that the examples we write are too naive;

So I found some information on the Internet and wrote another one;

 

 

Package com. example. demo; public class HttpUtils {// volatile is used as the command keyword to ensure that this command is not omitted due to compiler optimization, and the value must be read directly each time. // a variable defined as volatile means that this variable may be unexpectedly changed. // in this way, the compiler will not assume the value of this variable. // Precisely, the optimizer must carefully re-read the value of this variable every time when using this variable, rather than using the backup saved in the register. Private volatile static HttpUtils instance; private HttpUtils () {// constructor logic processing} public static HttpUtils getInstance () {// determines whether it is null for the first time if (instance = null) {synchronized (HttpUtils. class) {// lock // The second time when determining whether the thread is empty and going here at the same time, we need to optimize if (instance = null) {instance = new HttpUtils () ;}} return instance ;}}

Singleton mode, widely used in Android Framework;

For example:

1. InputMethodManager

2. View Distribution Management AccessibilityManager for click, focus, text change, and other events

 

 

public final class InputMethodManager {    static final boolean DEBUG = false;    static final String TAG = "InputMethodManager";    static final String PENDING_EVENT_COUNTER = "aq:imm";    static InputMethodManager sInstance;    InputMethodManager(IInputMethodManager service, Looper looper) {        mService = service;        mMainLooper = looper;        mH = new H(looper);        mIInputContext = new ControlledInputConnectionWrapper(looper,                mDummyInputConnection, this);    }    /**     * Retrieve the global InputMethodManager instance, creating it if it     * doesn't already exist.     * @hide     */    public static InputMethodManager getInstance() {        synchronized (InputMethodManager.class) {            if (sInstance == null) {                IBinder b = ServiceManager.getService(Context.INPUT_METHOD_SERVICE);                IInputMethodManager service = IInputMethodManager.Stub.asInterface(b);                sInstance = new InputMethodManager(service, Looper.getMainLooper());            }            return sInstance;        }    }        /**     * Private optimization: retrieve the global InputMethodManager instance,     * if it exists.     * @hide     */    public static InputMethodManager peekInstance() {        return sInstance;    }｝