[Chapter 5] 5.5 Canvas
Author: John Zukowski
Date: Thu Jul 31 14:34:37 1997

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| Chapter 5 Components |

## 5.5 Canvas

A `Canvas` is a class just waiting to be subclassed. Through `Canvas`, you can create additional AWT objects that are not provided by the base classes. `Canvas` is also useful as a drawing area, particularly when additional components are on the screen. It is tempting to draw directly onto a `Container`, but this often isn't a good idea. Anything you draw might disappear underneath the components you add to the container. When you are drawing on a container, you are essentially drawing on the background. The container's layout manager doesn't know anything about what you have drawn and won't arrange components with your artwork in mind. To be safe, do your drawing onto a `Canvas` and place that `Canvas` in a `Container`.

### Canvas Methods

Constructors

public Canvas ()

  The constructor creates a new `Canvas` with no default size. If you place the canvas in a container, the container's layout manager sizes the canvas for you. If you aren't placing the canvas in a container, call `setBounds()` to specify the canvas's size.

  Java 1.0 used the default constructor for `Canvas`; there was no explicit constructor.

Miscellaneous methods

public void paint (Graphics g)

  The default implementation of the `paint()` method colors the entire `Canvas` with the current background color. When you subclass this method, your `paint()` method needs to draw whatever should be shown on the canvas.

public synchronized void addNotify ()

  The `addNotify()` method creates the `Canvas` peer. If you override this method, first call `super.addNotify()`, then add your customizations. Then you can do everything you need with the information about the newly created peer.

### Canvas Events

The `Canvas` peer passes all events to you, which is why it's well suited to creating your own components.

A Simple Calculator |  | Creating Your Own Component