cs15 lecture 9 final 10-02-14 print

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Method OverloadingReview

Method Overloading (1/4)● Can define multiple methods

of same name within a class,as long as method signaturesare different

● Example: java.lang.Math● static method max takes in

two numbers and returns thegreater of the two

● There are actually three maxmethods-- one for ints, onefor floats, one for doubles

// this is an approximation of what Math’s// three max methods look likepublic class Math {

// other code elided

public static int max(int a, int b) {// return max of two ints

}

public static float max(float a, float b) {// return max of two floats

}

public static double max(double a,double b){

// return max of two doubles}

}

● Methods in same class withsame name but differentparameter lists

● When calling an overloadedmethod, Java infers whichmethod you mean based onparmeter list

● Thus cannot have two methodswith identical signatures butdifferent return types—compilererror because Java can’tdetermine which to call!




}


}



}

Method Overloading (2/4)● Be careful not to confuse

overloading and overriding!o override an inherited

method in a subclass: thesignatures (name; number,types, and order ofparameters) must be thesame

o overload methods in thesame class: names aresame, but signatures mustbe different




}


}



}

Method Overloading (3/4)

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● If neither overriding nor overloading: Can use same name,indeed signatures for methods in different classes

o Java can differentiate by type of instance on whichmethod is called during method resolution

o for example: if classes Car and Dog both have a movemethod that takes in one parameter of type int, Javaknows to use the Dog’s move when called on aninstance of Dog:

Dog dog = new Dog();

Car car = new Car();

dog.move(1); //Dog’s move method is called.car.move(1); //Car’s move method is called.

Method Overloading (4/4) Method Overloading: Constructors● Even constructors can be

overloaded! Wardrobe classhas multiple constructors

● A String (java.lang.String)is a sequence of alphanumericcharacters, including space!

● Example:String s = “CS15 Rocks!”;

● Can use System.out.printlnto print any string you want:

System.out.println(s);

public class Wardrobe {private String _top;private String _bottom;

public Wardrobe(String top, String bottom) {_top = top;_bottom = bottom;

}

public Wardrobe(String top) {_top = top;_bottom = “Jeans”;

}

public Wardrobe() {_top = “T-Shirt”;_bottom = “Jeans”;

}}

Method Overloading: Example

public class Plastic {

public Plastic(BurnBook myBurnBook) {DirtySecret secret = myBurnBook.getDirtySecret();this.backStab(secret);

}

public void backStab(DirtySecret secret) {String victim = secret.getVictim(); //find out whose secret it isthis.backStab(victim, secret);

}

public void backStab(String victim, DirtySecret secret) {//code to backstab elided (we don’t teach you how to backstab!)

}//other methods elided}

● An overloaded method can call other overloaded methodsLecture 9

Intro to Swing0 of 95

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What is Swing?● Swing is an API (Application Programming

interface)o part of core Java libraryo used to create applications with 2D graphics

● Frequently used classes in javax.swing packageo javax.swing.JFrame– the main window used

by your appo javax.swing.JPanel-- a canvas that contains

graphical componentso javax.swing.JButton-- a clickable button

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JPanelJButtons

JFrame

Creating Applications from Scratch

● Until now, TAs took care of graphicalcomponents for you

● Support code created JFrame, JPanels, allgraphical components

● From now on, you’re in charge of this!

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Graphical User Interfaces (GUIs)

● GUIs provide a user-controlled (i.e.,graphical) way to sendmessages to a systemof objects

● You’ll use Swing tocreate your own GUIsthroughout the semester

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Pixels and Coordinate System

● The screen is a grid ofpixels (tiny dots)

● Integer Cartesian plane with:o origin in upper-left cornero y-axis increasing downwardo corresponds to Latin-based

languages’ writing order

(0, 0)

Y

X

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Pixels and Coordinate System

● When working with Swing,you’ll be able to set the sizeand location of differentcomponents (panels, buttons,etc.) in pixels

● The “location” of eachcomponent will be thelocation of its top left corner

(0, 0)

Y

X

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Creating GUIs with Swing● Pattern: instantiate the

Swing components youneed and add them tographical containers

● Start with JFrame

JFrame

● Add JPanel to JFrame

● Add JButtons,JLabels, etc. to JPanel

JPanel

Hello, World!JLabel

JButtons

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Creating GUIs with Swing● Swing uses a default

layout to arrangecomponents in a JFrameor JPanel

● We’ll learn how tocustomize layout later inlecture

● For now, let Swing do itfor us

JFrame

JPanel

Hello, World!JLabel

JButtons

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Our First Swing Application

● Spec: app that contains textreading “CS15 Rocks!” andbutton that randomlychanges the text’s color withevery click

● Useful classes: JFrame,JPanel, JLabel, JButton,and ActionListener

JFrame

JLabel

JButtonJPanel

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DEMO: ColorTextApp

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JFrame

JLabel

JButtonJPanel

Process1. Create a top-level App class that

contains an instance of JFrame2. Create a subclass of JPanel that

contains an instance of JButton andan instance of JLabel

3. Add an instance of your JPanelsubclass to the JFrame

4. Set up an ActionListener thatchanges the label’s color each timethe button is clicked

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JFrame

JLabel

JButtonJPanel

● This is our top-levelclass

● It contains the JFrame(window in which theapp will display) as acomponent

public class ColorTextApp {

public ColorTextApp() {JFrame frame = new JFrame();frame.setDefaultCloseOperation(

JFrame.EXIT_ON_CLOSE);

frame.setVisible(true);}

public static void main(String[] args) {new ColorTextApp();

}}

Top-level Class: ColorTextApp

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● First we instantiate aJFrame, which we store inlocal variable frame

● Note: these slides will omitimport statements at top offile

Top-level Class: ColorTextApppublic class ColorTextApp {





}}

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● Next we call setDefaultCloseOperation onour JFrame

● This method specifies what happens whenuser hits “x” in corner of the JFrame

● Pass in constant JFrame.EXIT_ON_CLOSEas an argument so app will quit when wepress the “x”

● Swing magic keeps JFrames and theircontents alive as long as the “x” is notpressed, so they will not be “garbage-collected!” (Java GC’s variables when theygo out of scope – cease to exist)






}}

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● Finally, we call the methodsetVisible on our JFrame

● Pass in boolean value trueas an argument

● This makes the JFrame showup!

● Pro tip: Always call thismethod last to avoid nastylayout bugs






}}

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contains an instance of JButtonand an instance of JLabel



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JFrame

JLabel

JButtonJPanel

● The classColorTextPanel “is a”JPanel: our canvas thatmay contain other SwingGUI components

● We’ve specialized thisclass to contain anddisplay a JLabel and aJbutton (local vars)

public class ColorTextPanel extends JPanel {

public ColorTextPanel() {JLabel label = new JLabel("CS15 Rocks!");JButton button = new JButton("Random Color");

Dimension panelSize = new Dimension(150, 75);this.setPreferredSize(panelSize);this.add(label);this.add(button);

}}

JPanel Subclass: ColorTextPanel

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}}

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● First, we instantiate aJLabel and JButton

● In each case, we pass ina String as an argument

● This String is the text wewant the label/button todisplay○ Here we pass the

string as a “literal”;could also pass astring variable

● Now we set the “preferredsize” of our panel

● First, instantiate a Dimension(object that represents awidth and height, in pixels)

● First argument is width,second is height

● Then call methodsetPreferredSize on panel,passing in the Dimension asan argument





}}

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● Finally, we add the labeland button to the panel bycalling the panel’s addmethod

● This is a necessary stepfor the label and button toshow up!

The ColorTextPanel class




}}

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JFrame

JLabel

JButtonJPanel

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● First, instantiate a newColorTextPanel

● Then, add it to the JFrame bycalling the add method

● Finally, call the method packon the JFrame

o “pack” tells frame to resizeitself based on thepreferred sizes of thecomponents inside it

The ColorTextApp classpublic class ColorTextApp {



JPanel panel = new ColorTextPanel();frame.add(panel);frame.pack();



}}

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4. Set up an ActionListener thatchanges the label’s color eachtime the button is clicked

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JFrame

JLabel

JButtonJPanel

● Need a way to respond to stimulus of buttonbeing clicked

● We refer to this as event handling

o A source generates an event (like amouse click or a key press) and notifiesall registered listeners

o Each listener has a method forresponding to the event

o stimulus-response mechanism that allowsmultiple listeners to respond

Responding to User Input

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● Whenever a JButton is clicked, it generates ajava.awt.event.ActionEvent

● We define class that listens for ActionEvents: mustimplement interface java.awt.event.ActionListener

● ActionListener interface declares method:public void actionPerformed(ActionEvent e);

● This method must be defined in our listener classo called by Java whenever an ActionEvent is firedo specifies response to event

ActionListeners

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ActionListeners

Click!

JButton

ActionListener

ActionEvent e

public void actionPerformed( ) {

// Respond here; may or may not use ActionEvent// (print something to the console,// tell a JLabel to change color, etc.)

}

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ActionEvent e

Our ActionListener: ColorListener

● Our listener class isColorListener

● Its job is to listen forActionEvents andrespond to them bychanging the color of aJLabel

public class ColorListener implements ActionListener {private JLabel _label; //associated label

public ColorListener(JLabel label) {_label = label; }

@Overridepublic void actionPerformed(ActionEvent e) {

int red = (int) (Math.random()*256);int green = (int) (Math.random()*256);int blue = (int) (Math.random()*256);Color random = new Color(red, green, blue);_label.setForeground(random);

}}

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● Associated with a JLabel,which it refers to as_label-- a ColorListenerwill be passed the JLabelwhose color it shouldchange

● When ActionEvent isdetected, will change_label’s color

public class ColorListener implements ActionListener {private JLabel _label;

public ColorListener(JLabel label) {_label = label;

}



}}

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● actionPerformed definesresponse to ActionEvent

● In this case, we want it togenerate a random color,and then set _label to thatcolor



}



}}

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● Use Math.random() togenerate three random ints0-255

● Use them as RGB valuesfor a new Color

● Call JLabel methodsetForeground on _labelto set its color to the randomcolor we’ve created



}



}}

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Adding ActionListenerspublic class ColorTextPanel extends JPanel {


ColorListener listener =new ColorListener(label);

button.addActionListener(listener);


}}

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● First, instantiate a ColorListener● Pass in label as argument to

listener’s constructor so it knows tochange label’s color

● Next, use methodaddActionListener to add ourColorListener to button

○ Typical pattern: listeners areadded to the event-emittingcomponent they listen to

● Whenever button emits anActionEvent, listener will hear andrespond to it

Process

1. Create a top-level App class thatcontains an instance of JFrame

2. Create a subclass of JFrame thatcontains an instance of JButton andan instance of JLabel

3. Add a JPanel to the JFrame


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JFrame

JLabel

JButtonJPanel

The Whole Apppublic class ColorTextPanel extends JPanel {

public ColorTextPanel() {JLabel label = new JLabel("CS15 Rocks!");JButton button = new JButton("Random Color");ColorListener listener = new ColorListener(label);button.addActionListener(listener);Dimension panelSize = new Dimension(150, 75);this.setPreferredSize(panelSize);this.add(label);this.add(button);

}}



}



}}

public class ColorTextApp {



JPanel panel = new ColorTextPanel();frame.add(panel);frame.pack();



}}

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Putting It All Together

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ColorTextApp

JButton

ColorTextPanel

JLabel ColorListener

JFrame

Logical vs. Graphical Containment

● Graphically, the ColorTextPanel is contained within the JFrame, but logically, both arecontained together in a top-level App class; App and ColorListener aren’t graphic!

● Logical containment is based on where objects are created, while graphical is based on swingelements being added to other swing elements via the add(…) method

● Note: The JButton also has a reference to ColorListener, but this reference is omitted from ourdiagram to avoid excessive complexity.

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JFrame

JLabel

JButtonJPanel

ColorTextApp

JButton

ColorTextPanel

JLabel ColorListener

JFrame

Another Swing App: Clock

● Specifications: Appshould display thecurrent date and time,updating every second

● Useful classes: JFrame,JPanel, JLabel, Timer,ActionListener

JFrame

JLabelJPanel

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DEMO: Clock

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Using Timers● The class javax.swing.Timer comes in handy when we

need to perform a task repeatedly at regular intervals● When we instantiate a Timer, we pass it:

o An int (number of milliseconds between Timer ticks)o An ActionListener that should be notified when the

Timer emits an ActionEvent (on every tick)● We’re going to use a Timer to update the time displayed

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Using Timers

Timer

ActionListener

ActionEvent e

Tick!

public void actionPerformed( ) {

// Respond to ActionEvent here!// (print something to the console, tell// a JLabel to update its text, etc.)

}

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ActionEvent e

Process: Clock1. Create top-level class that

contains a JFrame

2. Write a subclass of JPanel thatcontains a JLabel. Add aninstance of it to our JFrame

3. Write a class that implementsActionListener-- it should knowabout a JLabel and update itstext on every ActionEvent

4. Instantiate a listener and a Timer,and start the Timer

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JFrame

JLabelJPanel

● As in the previousexample, we create a top-level class that contains aJFrame

● Specify closing behavior ofJFrame the same way wedid last time

Top-level Class: Clockpublic class Clock {

public Clock() {JFrame frame = new JFrame();frame.setDefaultCloseOperation(


frame.pack();frame.setVisible(true);

}

public static void main(String[] args) {new Clock();

}}

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● Call pack on the JFrame soit will resize itself based onits contents (which we’ll beadding soon)

● Last, make the frame showup by calling“setVisible(true); ”

Top-level Class: Clockpublic class Clock {




}


}}

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1. Create top-level class thatcontains a JFrame


3. Write a class that implementsActionListener -- it shouldknow about a JLabel and updateits text on every ActionEvent

4. Instantiate a listener and a Timer,and start the Timer

Process: Clock

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JFrame

JLabelJPanel

● We’ll call our JPanelsubclass “ClockPanel”

● As in previous example,create a Dimension torepresent desired width andheight of panel

● Call setPreferredSize onpanel, passing in theDimension we created

JPanel subclass: ClockPanel

public class ClockPanel extends JPanel {

public ClockPanel() {Dimension panelSize =

new Dimension(250, 50);this.setPreferredSize(panelSize);

JLabel timeLabel = new JLabel();this.add(timeLabel);

}}

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● Instantiate a JLabel, whichwill be used to displaycurrent time

● Add the JLabel to ourpanel

JPanel subclass: ClockPanel

public class ClockPanel extends JPanel {

public ClockPanel() {Dimension panelSize =

new Dimension(250, 50);this.setPreferredSize(panelSize);


}}

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● Back in our top-level class● After instantiating our

JFrame, we instantiate aClockPanel and add it tothe frame

Adding a ClockPanel to our JFramepublic class Clock {



ClockPanel panel = new ClockPanel();frame.add(panel);


}


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contains a JFrame


3. Write a class that implementsActionListener-- it shouldknow about a JLabel andupdate its text on everyActionEvent

4. Instantiate a listener and a Timer,and start the Timer 46 of 95

JFrame

JLabelJPanel

Our ActionListener: TimerListener

● A TimerListener’s job willbe responding toActionEvents fired by aTimer

● Knows about a particularJLabel, whose text it willmodify with everyActionEvent

public class TimerListenerimplements ActionListener {

private JLabel _timeLabel; //associated label

public TimerListener(JLabel label) {_timeLabel = label; }


long currTime = System.currentTimeMillis();Date now = new Date(currTime);_timeLabel.setText(now.toString());

}}

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Our ActionListener: TimerListener● When ActionEvent fires, we

first determine current dateand time

● System.currentTimeMillisreturns number ofmilliseconds elapsed sincemidnight January 1, 1970

● Can convert this number tothe actual date and time bypassing it into a newjava.util.Date


private JLabel _timeLabel;

public TimerListener(JLabel label) {_timeLabel = label;

}



}}

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Our ActionListener: TimerListener

● Next, we convert our Dateobject to a String using itstoString method

● We pass the resulting datestring into _timeLabel’ssetText method to update_timeLabel’s text


private JLabel _timeLabel;


}



}}

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contains a JFrame


3. Write a class that implementsActionListener-- it should knowabout a JLabel and update itstext on every ActionEvent

4. Instantiate a listener and aTimer, and start the Timer

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JFrame

JLabelJPanel

● In constructor ofClockPanel class, weinstantiate a newTimerListener

● Pass in our JLabel,timeLabel, as an argumentso the TimerListener willupdate its text

Instantiating a TimerListenerpublic class ClockPanel extends JPanel {

private Timer _timer;public ClockPanel() {

Dimension panelSize =new Dimension(250, 50);

this.setPreferredSize(panelSize);


TimerListener listener =new TimerListener(timeLabel);

_timer = new Timer(100, listener);_timer.start();

}}

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● Next, instantiate a new Timer,and store it in instancevariable _timer

o first argument is number ofms between “ticks”

o second argument is thelistener that will be notifiedon every tick

● Don’t forget to call start onthe Timer!

Instantiating and starting a Timerpublic class ClockPanel extends JPanel {


Dimension panelSize =new Dimension(250, 50);

this.setPreferredSize(panelSize);


TimerListener listener =new TimerListener(timeLabel);

_timer = new Timer(100, listener);_timer.start();

}}

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The Whole Apppublic class ClockPanel extends JPanel {


Dimension panelSize = new Dimension(250, 50);this.setPreferredSize(panelSize);


TimerListener listener = new TimerListener(timeLabel);_timer = new Timer(100, listener);_timer.start();

}}public class TimerListener

implements ActionListener {private JLabel _timeLabel;


}



}}

public class Clock {



ClockPanel panel = new ClockPanel();frame.add(panel);


}


}}

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Putting It All Together: Clock

Clock

JFrame

JLabel TimerTimerListener

ClockPanel

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A Third Swing App: ColorPanelApp

● Specification: An appwith three sliders thatthe user can drag tochange the RGB valuesof the background color

● Useful classes: JFrame,JPanel, JSlider,ChangeListener

JFrame

JSliderJPanel

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DEMO: ColorPanelApp

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● A JSlider lets the user graphically select a value bysliding an arrow within a bounded interval

● One way to construct is by passing two ints (minimumand maximum values) as arguments:

JSlider slider = new JSlider(0, 30);● To get the value of the slider, we can use the getValue

method● A JSlider emits ChangeEvents when value changes--

to listen for them, we use a ChangeListener

Using JSliders

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ChangeListeners ChangeListener

public void stateChanged( ) {

// Respond to ChangeEvent here!// (print something to the console, tell// a JLabel to update its text, etc.)

}

JSlider

ChangeEvent e

ChangeEvent e

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Process: ColorPanelApp1. Create top-level class that

contains a JFrame

2. Write a subclass of JPanel thatcontains three JSliders, add aninstance of it to the JFrame

3. Write a ChangeListener thatchanges a JPanel’s color basedon value of a JSlider

4. Add ChangeListeners to theJSliders

JFrame

JSliderJPanel

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Top-level Class: ColorPanelApp

● This top-level class isalmost identical tothose of the otherexamples-- we followsame pattern of settingup JFrame

● Instantiate JFrame, setits close operation, callpack and setVisible

public class ColorPanelApp {

public ColorPanelApp() {JFrame frame = new JFrame();frame.setDefaultCloseOperation(



}

public static void main(String[] args) {new ColorPanelApp();

}}

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contains a JFrame

2. Write a subclass of JPanelthat contains three JSliders,add an instance of it to theJFrame



JFrame

JSliderJPanel

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JPanel Subclass: ColorPanel

● ColorPanel “is a”JPanel

● As in other examples,create a Dimension,give it desired widthand height, then callsetPreferredSize

● Want panel to start outgray, so call methodsetBackground

public class ColorPanel extends JPanel {

public ColorPanel() {Dimension panelSize = new Dimension(300, 150);this.setPreferredSize(panelSize);this.setBackground(Color.GRAY);JSlider sliderRed = new JSlider(0, 255);JSlider sliderGreen = new JSlider(0, 255);JSlider sliderBlue = new JSlider(0, 255);

this.add(sliderRed);this.add(sliderGreen);this.add(sliderBlue);

}}

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JPanel Subclass: ColorPanel● Instantiate three

JSliders: one tocontrol each channel(red, green, and blue)

● Arguments arebeginning/end ofslider’s range: we giveeach range 0-255 (onebyte/RGB channel)

● Finally, add each sliderto panel




}}

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Adding a ColorPanelApp to the JFrame

● Just as we did inprevious examples,first instantiate a panel,then call add to add itto the JFrame




ColorPanel panel = new ColorPanel();frame.add(panel);


}


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contains a JFrame


3. Write a ChangeListener thatchanges a JPanel’s colorbased on value of a JSlider


JFrame

JSliderJPanel

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Changing a JPanel’s Color● Every JPanel has a pair of accessor and mutator methods,

setBackground and getBackground

● We have three JSliders-- one to control each color channel of theJpanel. Each Jslider has its own listener

● When red slider’s listener detects that its slider has been moved:o it calls getBackground to ask the panel for its current coloro it creates a new instance of Color, using the “R” value from the

slider and the “G” and “B” values from the panel’s currentbackground color (since they haven’t changed)

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Our ChangeListener: SliderListener● A SliderListener’s job is to

change the color of a JPanelbased on the value of a JSlider

● Since JSliders emitChangeEvents whenever theirvalue changes, SliderListenerimplements ChangeListenerinterface

● Defines method stateChanged.SliderListener will be codedgenerically so it can be used foreach slider

public class SliderListenerimplements ChangeListener {

private JPanel _panel;private int _channel;private JSlider _slider;

public SliderListener(JPanel panel, int channel,JSlider slider){

_panel = panel;_channel = channel;_slider = slider;

}

@Overridepublic void stateChanged(ChangeEvent e) {

// implementation elided for now}

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Our ChangeListener: SliderListener● To do its job, it needs to know

three things:

o The JPanel whose colorit should change

o Which channel (red,green, or blue) to modify

o Which slider it listens to

● We’ll represent the channel asan int: 0 means red, 1 meansgreen, 2 means blue


private JPanel _panel;private int _channel;private JSlider _slider;

public SliderListener(JPanel panel, int channel,JSlider slider){

_panel = panel;_channel = channel;_slider = slider;

}


// implementation elided for now}

} 68 of 95

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The stateChanged method● Method is called whenever

value of the listener’s JSliderchanges

● Should modify the appropriatecolor channel of the JPanel’sbackground color

● Must take in a ChangeEventas a parameter, because it isrequired by theChangeListener interface;doesn’t use it in this case

// rest of class SliderListener elided for now@Overridepublic void stateChanged(ChangeEvent e) {

int val = _slider.getValue();Color bg = _panel.getBackground();Color newbg;

switch(_channel){case 0:

newbg = new Color(val, bg.getGreen(),bg.getBlue());

break;case 1:

newbg = new Color(bg.getRed(), val,bg.getBlue());

break;default:

newbg = new Color(bg.getRed(), bg.getGreen(),val);

}_panel.setBackground(newbg);

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The stateChanged method

● Need to determine new value ofJSlider

● Since we know the source is theJSlider, we can retrieve valueby calling getValue on _slider





break;case 1:


break;default:



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● Next, we get the JPanel’scurrent background color

● We declare a new Color, newBg,to which we’ll assign a differentvalue based on which colorchannel the listener is supposedto change





break;case 1:


break;default:



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● Depending on the value of_channel, we set newBg to adifferent color

● In each case, only the specifiedcolor channel changes; we usethe gets for the values of theunchanged channels

● Once we’ve changed theappropriate channel, we set theJPanel’s background color tonewBg





break;case 1:


break;default:



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contains a JFrame




JFrame

JSliderJPanel

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Setting up our SliderListeners● Back in ColorPanel

class● Call method

addChangeListener oneach slider, passing in anew instance ofSliderListener

● Pass in ColorPanel,appropriate channelnumber and slider asarguments to eachSliderListener


public ColorPanel() {Dimension panelSize = new Dimension(300, 150);this.setPreferredSize(panelSize);this.setBackground(Color.GRAY);JSlider sliderRed = new JSlider(0, 255);JSlider sliderGreen = new JSlider(0, 255);JSlider sliderBlue = new JSlider(0, 255);sliderRed.addChangeListener(

new SliderListener(this, 0, sliderRed));sliderGreen.addChangeListener(

new SliderListener(this, 1, sliderGreen));sliderBlue.addChangeListener(

new SliderListener(this, 2, sliderBlue));this.add(sliderRed);this.add(sliderGreen);this.add(sliderBlue);

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The Whole App (1/2)public class ColorPanel extends JPanel {


sliderRed.addChangeListener(new SliderListener(this, 0, sliderRed));

sliderGreen.addChangeListener(new SliderListener(this, 1, sliderGreen));

sliderBlue.addChangeListener(new SliderListener(this, 2, sliderBlue));


}}




ColorPanel panel = new ColorPanel();frame.add(panel);


}


}}

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The Whole App (2/2)


private JPanel _panel;private int _channel;

public SliderListener(JPanel panel, int channel){_panel = panel;_channel = channel;

}


int val = _slider.getValue();Color bg = _panel.getBackground();Color newbg;switch(_channel){case 0:


break;case 1:


break;default:


}_panel.setBackground(newbg); }

}

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Putting It All Together: ColorPanelApp

ColorPanelApp

JFrame ColorPanel

JSlider SliderListener

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Buttons in Swing

Some buttons in Swing:● javax.swing.JButton● javax.swing.JToggleButton● javax.swing.JCheckBox● javax.swing.JRadioButton

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Buttons in Swing

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ButtonGroups

● How do we make options mutually exclusive(i.e. you can only click one button at a time)?o put them in a button groupo javax.swing.ButtonGroup

● Buttons that can be added to ButtonGroup:JRadioButtonJToggleButtonJMenuItem (for advanced users)

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JRadioButtons & ButtonGroups

● How to use a ButtonGroup:o create buttons

JRadioButton rB1 = new JRadioButton(“Green, not Red”);JRadioButton rB2 = new JRadioButton(“Red, not Green”);

o create ButtonGroupButtonGroup bGroup = new ButtonGroup();

o add buttons to ButtonGroupbGroup.add(rB1);bGroup.add(rB2);

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public class RadioColorListener implements ActionListener {private JLabel _label;private Color _currentColorpublic RadioColorListener(JLabel label, Color color) {

_label = label;_currentColor = color;

}@Overridepublic void actionPerformed(ActionEvent e) {

_label.setForeground(_currentColor);}

}

Modified ColorTextApp: RadioColorListener

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Modified ColorTextApp: ColorTextPanelpublic class ColorTextPanel extends JPanel {

public ColorTextPanel() {JLabel label = new JLabel("CS15 Rocks!");JRadioButton buttonForRed = new JRadioButton("Red");JRadioButton buttonForGreen = new JRadioButton(“Green);RadioColorListener redListener = new RadioColorListener(label, Color.RED);RadioColorListener greenListener = new RadioColorListener(label, Color.GREEN);

//add listeners to their buttonsbuttonForRed.addActionListener(redListener);buttonForGreen.addActionListener(greenListener);

//create button group and add buttons to itButtonGroup buttonGroup = new ButtonGroup();buttonGroup.add(buttonForRed);buttonGroup.add(buttonForGreen);Dimension panelSize = new Dimension(300, 100);this.setPreferredSize(panelSize);

//add label and buttons to ColorTextPanelthis.add(label);this.add(buttonForRed);this.add(buttonForGreen);

}}

Assume all the swingcomponents areimported!

For more complex projectsyou might want to give theButtons a separate JPaneland use LayoutManagers(stay tuned!)

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More Complicated Swing Apps

● The examples we’ve seen so far have been small andsimple

● What if we want to construct a more realistic GUI?● We can use LayoutManagers to arrange components

nicely within JPanels

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Using java.awt.LayoutManagers● Each JPanel contains a LayoutManager to

automatically arrange its sub-components● LayoutManager interface implemented by classes:

o java.awt.FlowLayouto java.awt.GridLayouto java.awt.BorderLayout

● To specify the LayoutManager for a JPanel, eitherpass an instance of one of these classes to the panel’sconstructor or to its setLayout method later 85 of 95 93/106

FlowLayout

● Default layout used byall JPanels

● Arranges componentsfrom left to right, top tobottom

● When it reaches theedge of the panel,moves to next row

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public class FlowTest extends JFrame {

public FlowTest() {super();this.setSize(200, 300);JButton b1 = new JButton(“One”);JButton b2 = new JButton(“Two”);JButton b3 = new JButton(“Tree”);JButton b4 = new JButton(“Four”);JButton b5 = new JButton(“Five”);JButton b6 = new JButton(“Six”);JPanel mainPanel = new JPanel();

FlowLayout fl = new Flowlayout();mainPanel.setLayout(fl);mainPanel.add(b1);mainPanel.add(b2);mainPanel.add(b3);mainPanel.add(b4);mainPanel.add(b5);mainPanel.add(b6);this.add(mainPanel);this.pack();this.setVisible(true);

}}

FlowLayout

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GridLayout● Arranges components in

a grid● Add components left to

right, top to bottom● Must specify grid size in

constructor-- number ofrows and columns

● Each cell in grid is samesize, determined bylargest element in grid 95 of 95

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public class GridTest extends JFrame {

public GridTest() {super();this.setSize(200, 300);JPanel p1 = new JPanel();JPanel p2 = new JPanel();JPanel p3 = new JPanel();JPanel p4 = new JPanel();JPanel p5 = new JPanel();JPanel p6 = new JPanel();JPanel mainPanel = new JPanel();

p1.setBackground(Color.GREEN);p2.setBackground(Color.RED);p3.setBackground(Color.ORANGE);p4.setBackground(Color.CYAN);p5.setBackground(Color.BLUE);p6.setBackground(Color.YELLOW);

GridLayout gl = new GridLayout(3, 2);mainPanel.setLayout(gl);mainPanel.add(p1);mainPanel.add(p2);mainPanel.add(p3);mainPanel.add(p4);mainPanel.add(p5);mainPanel.add(p6);this.add(mainPanel);this.pack();this.setVisible(true);

}}

GridLayout

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BorderLayout

● Splits JPanel into 5regions: NORTH, SOUTH,EAST, WEST, CENTERo These are all static

constants● Must specify region when

adding component to itscontainer

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BorderLayout

● Don’t have to fill allregions-- default size of aregion is (0, 0)

● BorderLayout will adjustdynamically dependingon what has been added

● Typically add to CENTERfirst-- it should be largest

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BorderLayoutpublic class BorderTest extends JFrame {

public BorderTest() {super();this.setSize(300, 200);JPanel p1 = new JPanel();JPanel p2 = new JPanel();JPanel p3 = new JPanel();JPanel p4 = new JPanel();JPanel p5 = new JPanel();JPanel mainPanel = new JPanel();

p1.setBackground(Color.RED);p2.setBackground(Color.GREEN);p3.setBackground(Color.ORANGE);p4.setBackground(Color.CYAN);p5.setBackground(Color.BLUE);

BorderLayout bl = new BorderLayout();mainPanel.setLayout(bl);mainPanel.add(p1, BorderLayout.CENTER);mainPanel.add(p2, BorderLayout.NORTH);mainPanel.add(p3, BorderLayout.SOUTH);mainPanel.add(p4, BorderLayout.EAST);mainPanel.add(p5, BorderLayout.WEST);this.add(mainPanel);this.pack();this.setVisible(true);

}} 92 of 95

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LayoutManagers● You’ll be using layouts a lot in

CS15-- practice playing aroundwith them!

● Try taking the previous exampleand calling setPreferredSizeon each sub-panel to changetheir sizes and shapes

● If you want to test yourunderstanding (and want to geta headstart on Cartoon), trymaking something like this:

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LayoutManagers

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Swing: Summary● Swing has a variety of tools to help you make

GUIs:o JFrames, JPanels, JButtons, and JSliders, arranged using

LayoutManagerso ActionListeners and ChangeListeners to respond to user inputo Timers to perform a task at regular intervals

● On future projects, instead of relying on supportcode for graphical elements, you will use thesetools yourself!

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Announcements● On-time Due Date for TASafeHouse is Friday,

October 3rd, at 10:00 PM

● Late Due Date for TASafeHouse is Sunday,October 5th, at 11:59 PM

cs15 lecture 9 final 10-02-14 print

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