单例模式

public final class WindowManagerGlobal {
    private static final String TAG = "WindowManager";


    private static WindowManagerGlobal sDefaultWindowManager;
    private WindowManagerGlobal() {
    }
    public static WindowManagerGlobal getInstance() {
        synchronized (WindowManagerGlobal.class) {
            if (sDefaultWindowManager == null) {
                sDefaultWindowManager = new WindowManagerGlobal();
            }
            return sDefaultWindowManager;
        }
    }
}