CMPT 270: Custom JComponents and Graphics

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Questions and Answers

What is the first step in creating a custom JComponent?

  • Override the paintComponent method
  • Create a class that inherits from JComponent (correct)
  • Set the current color in the graphics context
  • Invoke the repaint() method

What method must be overridden to customize the appearance of a JComponent?

  • paintComponent() (correct)
  • createComponent()
  • renderComponent()
  • drawComponent()

When is the paintComponent method called?

  • When the component is created and when the window resizes (correct)
  • Whenever the background color is changed
  • Only when the user interacts with the component
  • Only when the application starts

What type of parameter is passed into the paintComponent method?

<p>Graphics (C)</p> Signup and view all the answers

Which command is used to change the current color for drawing in a graphics context?

<p>g.setColor(Color) (C)</p> Signup and view all the answers

What does the repaint() method do for a JComponent?

<p>It forces the JComponent to render itself again. (C)</p> Signup and view all the answers

What is a common action performed with the Graphics object?

<p>Drawing shapes and setting colors (C)</p> Signup and view all the answers

After changing something in your program, what method do you call to ensure your component is updated on the screen?

<p>repaint() (A)</p> Signup and view all the answers

Flashcards

Custom JComponent

A class that extends the JComponent class to create a custom UI element.

paintComponent Method

A method that is called automatically when the component is created or needs to be redrawn, allowing developers to define how the component should be rendered.

Graphics Object

An object that provides tools for drawing shapes, lines, and text on the screen, allowing you to customize the appearance of your custom component.

g.setColor(Color)

A function of the Graphics object that allows you to set the color that will be used for subsequent drawing operations.

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g.drawRect(int x, int y, int width, int height)

Draws an empty rectangle with the specified width and height, using the current drawing color.

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g.fillRect(int x, int y, int width, int height)

Draws a filled rectangle with the specified width and height, using the current drawing color.

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repaint()

A method that requests the Java Swing system to redraw a specific component, often needed when the component's appearance needs an update.

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JComponent

It provides a framework for creating graphical user interfaces. It's a key part of Java's Swing toolkit, allowing developers to create complex and customizable interactive GUIs.

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Study Notes

CMPT 270: Developing Object Oriented Systems

  • Course focuses on graphics and custom JComponents
  • Learning objectives include:
    • Creating custom JComponents
    • Creating primitive graphics
    • Incorporating custom components into GUI Swing programs

Custom JComponents

  • Creating a custom JComponent is similar to creating a custom JFrame
  • To create a custom JComponent:
    • Create a class that inherits from JComponent
    • Override the paintComponent method
    • Write custom drawing code to customize the component's appearance

paintComponent Method

  • Automatically called on creation and window resizing
  • To redraw the component when needed, call the repaint() method on the component instance.
  • Accepts a Graphics object as a parameter
    • This object is used for drawing shapes and other graphical elements

Graphics Object and Graphics Context

  • The Graphics parameter provides a way to draw on a component.

  • The Graphics object offers various methods for drawing (like rectangles, ovals, lines)

  • Use g.setColor() to set the drawing color

  • The paintComponent method is the key method for custom drawing.

Drawing Commands

  • g.setColor(Color): Sets the drawing color
  • g.drawRect(int x, int y, int width, int height): Draws a rectangle
  • g.fillRect(int x, int y, int width, int height): Fills a rectangle
  • Other methods for drawing different shapes (oval, arc, polygon, roundRect), and images

Example paintComponent Method

  • Sets the color to red
  • Fills a rectangle at (0, 0) with dimensions 100x200
  • Sets the color to black
  • Draws an oval at (50, 50) with dimensions 75x75

Exercise 1: Creating a Healthbar

  • Create a functional health bar UI for a video game
  • Implement a Model–View–Controller architecture to manage player health
  • The View component will contain a custom HealthbarComponent.
  • This component changes size depending on the current health compared to maximum health
  • Add buttons for "damage" and "heal" to test the health bar
  • This exercise involves creating custom UI elements

Summary

  • Inherit from JComponent to build custom UI widgets.
  • Customize component appearance by overriding the paintComponent method.

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CMPT 270 Developing Object Oriented Systems PDF

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