CS51 - Spring 2010 - Lecture 11

  • Exercises 11.4.2 and 11.4.3

  • show ColorSlider demo
       - what's in the center?
          - canvas with a FilledRect
       - we can adjust the sliders and in response to that, our program updates the color
          - Another interface ChangeListener
             - one method: public void stateChanged(ChangeEvent evt)
             - similar to our other listeners, we have an: addChangeListener(this) method
          - this pattern should start to look familiar:
             - implements ChangeListener
             - add the stateChange method
             - tell the program that "this" will listen/respond to any changes made by the object (in this case, the sliders)
       - why do we have two different interfaces ActionListener and ChangeListener
       - what does our layout look like at the bottom?
          - compare 3 by 1 grids with nested 1 by 3 grids and one 3 by 3 grid

  • look at ColorSlider code
       - what information do you think we need to construct a new JSlider (i.e. what's going to go in the constructor)?
          - need to know whether it's a vertical or horizonal slider
          - range, specified by a minimum value and a maximum value
          - initial, starting value
       - what information for JLabels?
          - the text
          - the alignment
             - JLabel.RIGHT
             - JLabel.LEFT
             - JLabel.CENTER
       - to handle the changing sliders:
          - implements ChangeListener
          - stateChanged method: going to be called everytime any of the sliders changes values
          - addChangeListener(this) for the three sliders
       - what do we want to do when a slider changes value?
          - get the value from each of the sliders
             - getValue() method returns the value
          - set the color of our FilledRect to be the new color indicated by the sliders
          - update the text for all of the sliders
             - setText(...) (similar to setText for Text)
             - why do we do "" + redValue? what does this accomplish?
       - we could try and figure out which of the sliders changed using evt.getSource(), but it would just make the code more complicated

  • show ColorMixer demo
       - rather than using a JSlider, we can use a JTextField to allow the user to enter data
          - getText() method allows us to get the text entered in the JTextField
          - how do we know when to check the data?
             - when the user hits "return" it triggers an event
             - what type of listener do you think we would use?
                - ActionListener (discrete, user generate event)
                - we can addActionListener to respond to user inputs
       - what does the layout look like?
          - 3, 2 GridLayout
          - each row has a JLabel and a JTextField
       - when we're allowing a user to enter data, what do we need to be careful of?
          - need to make sure the the user enters valid data
             - in this case, it has to be a number and that number has to be between 0 and 255

  • look at ColorMixer code
       - when we're creating a GridLayout layout manager, there are two additional parameters we can specify (if we want) that modify the amount of space in between the rows and columns
          - new GridLayout(3, 2, 10, 5)
             - 3 rows
             - 2 columns
             - 10 pixel horizontal gap (i.e. between each column)
             - 5 pixel vertical gap (i.e. between each row)
       - addActionListener(this) for all of the JTextFields
       - actionPerformed method
          - get the text values
          - create a new color and set the color of the FilledRect
          - what does the getColorMix method do?
             - it's a private helper method
             - why is it private?
                - only used internally to the class
             - gets the value from the JTextField and checks to see if it's the appropriate range
             - what if it's not in the range?
                - if it's less than the minimum value, it's set to the minimum value
                - if it's larger than the maximum value, it's set to the maximum value
          - why use a helper method?
             - whenever you find yourself doing repeated work, make a method!

  • what if we want multiple lines of text, like a pararaph, etc?
       - JTextArea
       - same basic premise as JTextField, but multiple lines
       - look at the TextApplet example in the book

  • show Interesting demo

  • midterm review
       - worth 15% of your grade
          - note also that TP1 is worth 15% of your grade
          - make sure you put in the time for both of these
       - close book, closed notes, etc.
       - we will give you copies of:
          - Objectdraw quick reference
          - GUI cheat sheet
       - types of questions
          - 1-2 code this up problems
          - 1-2 what does this code do problems
          - a few short answer questions
       - will cover all the material up through now (including GUIs)
       - topics (roughly)
          - basic programming
             - variables
                - instance
                - local
                - constants
             - methods
             - classes
             - parameters
             - commenting
          - objectdraw components
          - booleans
          - if-else
          - ints and doubles
          - while loops
          - active objects
          - defining and manipulating multiple classes
          - GUIs
          - randomness
          - colors
          - images
          - audio
          - interfaces
    •