public final class InputMethodManager { 
static final Object mInstanceSync = new Object();//同步 
//内部全局唯一实例 
static InputMethodManager mInstance; 

//对外api 
static public InputMethodManager getInstance(Context context) { 
return getInstance(context.getMainLooper()); 
} 

/** 
* 内部api，供上面的外部api调用 
* @hide 系统隐藏的api 
*/ 
static public InputMethodManager getInstance(Looper mainLooper) { 
synchronized (mInstanceSync) { 
if (mInstance != null) { 
return mInstance; 
} 
IBinder b = ServiceManager.getService(Context.INPUT_METHOD_SERVICE); 
IInputMethodManager service = IInputMethodManager.Stub.asInterface(b); 
mInstance = new InputMethodManager(service, mainLooper); 
} 
return mInstance; 
} 
} 

class ContextImpl extends Context{ 
@Override 
public Object getSystemService(String name) { 
if (WINDOW_SERVICE.equals(name)) { 
//... ... 省略下面n个if，else if 
} else if (INPUT_METHOD_SERVICE.equals(name)) { 
//获取输入法管理者唯一实例 
return InputMethodManager.getInstance(this); 
} else if (KEYGUARD_SERVICE.equals(name)) { 
//... ... 省略下面n个if，else if 
} else if (ACCESSIBILITY_SERVICE.equals(name)) { 
//又见单例，无处不在 
return AccessibilityManager.getInstance(this); 
} else if (LOCATION_SERVICE.equals(name)) { 
//... ... 省略下面n个if，else if 
} else if (NFC_SERVICE.equals(name)) { 
return getNfcManager(); 
} 
return null; 
} 
}