Separation of concepts: What is the best way to create UI interfaces?

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Overview
To create the user interfaces there are two controls: Containers and Windows. Whatever you are drawing to be displayed to the user must be within one of those controls. In the next topics of this session we will understand what the function of each one is and what factors that make Containers or Windows are preferable in certain cases.
Differences Between Containers and Windows
First let's understand what the main function of each one is:
Definition
Container: is a control capable of containing other controls. It is primarily a form of organization. To fully understand the attributes and methods of this control, access the Container documentation in the API session by clicking below:
Container
Window: é a control capable of overlapping others, creating an illusion of depth. In addition, Windows is also containers, as they can accommodate several components within them. Windows allow animations, while the pure container exchange does not. As an example, we have the Sliding and the Material Window, which have more modern transition effects.
To fully understand which attributes and control methods, access the Windows documentation in the API session by clicking below: 
Window
Which one to use?
How much is thought in a MessageBox, it is clear that it is a Window and not only a Container, since it does not occupy the entire screen.
In cases where Window occupies the entire screen, the difference between Window and Container becomes narrower. A full screen window does not "delete" the screen underneath, it is still there. Ithis means that the status of the "bottom" screen remains unchanged. In addition, execution locks in the popup until unpop occurs (Windows are modal by default). 
In the case of container hot-swap exchanges, the container that left the scene actually leaves the scene and may even be deleted if no reference to it is retained.
Now that you know the definition of each becomes easier to identify where they should be used.
Best Practices
Opting for mixed approach is the best way to use UI controls well. For, as shown, using only Containers deprives you of having transition animations. Using only Windows can generate an overuse of resources (especially memory).
With the mixed approach, one searches for the best of both worlds. However, it is worth mentioning some extra points:
It's common for programmers to create whole systems for more control. It is not impossible to have a system of BaseContainers that can have animations or make a Windows system that is not heavy when there are many overlapping screens.
It is also important to take into account the designer's vision. Some applications do not need animated transitions or only use animated transitions. This kind of thing can help you decide which approach to use.
Finally, there are also other options. Using SideMenu is a form of pre-ready screen management. Some applications use a full screen TabbedContainer and switch screens with side swipes or programmatically. 
In cases of Processes and Flows of the application are "BaseContainers", since there is no need to keep the other screens in the background (and in memory) then we use Container.
As for the internal screens of a stream, it makes sense to use Windows and other features like Scroll or Tabbed Containers to perform transitions and organizations. You can have several examples of organization of interfaces in MaterialTemplates in github, where we created several interface templates following the recommendations of the Material.
In this way, Windows is used for animations and screen transitions within a stream and uses BaseContainers to switch from one stream to another of the application.
Taking a practical example, our implementation of SideMenu uses Containers for each screen and uses a TopMenu to create the Menu itself, which appears overlapping the current screen.
In TCSample,many of the screens use the Material Window to create a "second screen" within the current screen.
Navigating between interfaces
Container
To call a Container, just use:
swap(new InitialScreen()); - If you are in the Main Window and want to call a Container, simply use the swap() command.
MainWindow.getMainWindow().Swap(new SecondScreen()); - If you are in a container or Window and want to call a Container just use the command.
Window
To call a window, just use: 
.popup() - The execution stops after the popup()command is executed.
.popupNonBlocking() - the execution continues right after the popup command, even with the window still open.
Other Ways
As we mentioned in the previous topic, you can use BaseContainers to exchange flows in the application, in this case we use the show() and back().  See the example below:
BaseContainer_Sample
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public class BaseContainer extends Container {
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​
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    protected static final Vector containerStack = new Vector(5);
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​
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    public void show() {
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    	//containerStack.
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        containerStack.push(this); // push ourself
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        MainWindow.getMainWindow().swap(this);
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    }
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​
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    public void back() {
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        if (parent == null || getParentWindow() == Window.getTopMost()) {
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            try {
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                containerStack.pop();
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                MainWindow.getMainWindow().swap((Container)containerStack.peek());
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            } catch (ElementNotFoundException enfe) {
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                MainWindow.exit(0);
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            }
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        }
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    }
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}
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​
Copied!
Another way to work with interface changes without losing the data of each is through the design pattern called Singleton, where you will create a single object for which there is only one instance. To delve deeper into this pattern, just click here.
References
To better illustrate where each of them is used, you can download the Nubank_Sample project in GitHub.​
Reading JavaDoc can be very useful.
Data Persistence: DAO Pattern.
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Contents
Overview
Differences Between Containers and Windows
Definition
Which one to use?
Best Practices
Navigating between interfaces