Programming and Problem Solving With Java Copyright 1999, James M. Slack The Java Abstract Windowing...

Programming and Problem SolvingWith Java

Copyright 1999, James M. Slack

The Java Abstract Windowing ToolkitLayout and Layout ManagersComponentsPanelMenusFileDialogOther Capabilities of the AWT

Programming and Problem Solving With Java 2

Graphical User InterfacesMany programs have graphical user interface (GUI)

Windows IconsMenusPointing device

Advantages of GUI programsLooks up-to-dateDesktop metaphorMost users are familiar with GUI programs

Sometimes called

the “W.I.M.P.”

interface


Graphical User InterfacesDevelopment of GUI programs

Used to be very difficult and expensiveToday, visual development tools (like Visual Basic) make

GUI development much easier Just drag components onto the screen with mouse

Still expensive to develop cross-platform GUI appsPorting tools help a little

Java changes things Java GUI programs are source and object compatible

across platformsCan develop Java GUI programs with or without visual

development tools


Layout and Layout ManagersTwo ways to design graphical user interface in Java

Visual development tool: drag and drop componets on the screen (like Visual Basic)•JBuilder•VisualAge for Java•Visual Café•Visual J++

Use Java’s layout managers


Layout and Layout ManagersLayout manager

Automaticallyplacescomponents (buttons, text, ...) on the screen

Adjusts components if user resizes the window

This is the BorderLayoutlayout manager


Layout and Layout ManagersJava’s AWT has several layout managers

predefinedFlowLayoutBorderLayoutGridLayoutGridBagLayoutothers...

Also possible to define additional layout managersDifferent layout managers place components on the

screen in different ways

Will look at thesethree in detail


Layout and Layout ManagersFlowLayout

Simplest layout managerPuts components on window like word processor puts

words on a pageLeft-to-right, top-to-bottom

User Name: Password:

OK Cancel

User Name:

Password:

OK Cancel


Layout and Layout ManagersFlowlayout layout manager adjusts componets

when window size changesAgain, just like a word processor


OK Cancel


OK Cancel


Layout and Layout ManagersFrame

Window that knows how to resize itselfMoves around on the screen when draggedCan minimize, maximize


Layout and Layout ManagersHow to use Flowlayout

Import AWT packageimport java.awt.*;

Define a new class as a subclass of Frameclass FlowLayoutExample extends Frame{ ...}

Constructor steps// Make title for framesuper("FlowLayout Example");

// Initialize layout managersetLayout(new FlowLayout(FlowLayout.CENTER));

// Put components on frameadd(new Button("Hello"));add(new Button("There"));add(new Button("How are you?"));

// Set size of frame and show itsetSize(200, 100);show();


Layout and Layout Managers// Demonstrates how to use the FlowLayout layout manager.

import java.awt.*;

class FlowLayoutExample extends Frame{ // Constructor public FlowLayoutExample() { // Call the constructor for the Frame class with the title // for the window super("FlowLayout Example");

// Choose the layout manager and initialize it setLayout(new FlowLayout(FlowLayout.CENTER));

// Put components on the frame add(new Button("Hello")); add(new Button("There")); add(new Button("How are you?"));

// Set the size for the frame and display it setSize(200, 100); show(); }}

public class DemonstrateFlowLayout{ static public void main(String[] args) { new FlowLayoutExample(); }}

The whole

program


Layout and Layout ManagersResizing frame rearranges components

Flowlayout layout manager arranges components like a word processor arranges words


Layout and Layout ManagersBorderlayout

Divides frame into five areas: North, South, East, West, Center

Can put five components on frame


Layout and Layout ManagersResizing Borderlayout frame

Height of North andSouth are fixed

Width of East andWest are fixed

Other dimensionsgrow to fill frame


Layout and Layout ManagersBorderLayout Example

class BorderLayoutExample extends Frame{ // Constructor public BorderLayoutExample() { // Call the constructor for the Frame class with the title // for the window super("BorderLayout Example");

// Choose the layout manager and initialize it setLayout(new BorderLayout());

// Put components on the frame add(new Button("North"), BorderLayout.NORTH); add(new Button("South"), BorderLayout.SOUTH); add(new Button("West"), BorderLayout.WEST); add(new Button("East"), BorderLayout.EAST); add(new Button("Center"), BorderLayout.CENTER);

// Set the size for the frame and display it pack(); show(); }}

Must specifylocation

pack()makesframe

small aspossible


Layout and Layout ManagersGridLayout

Puts components into a matrix from left to right and from top to bottom

Specify size of matrix in instantiation of GridLayout object

Example: make a matrix with three rows and four columns

new GridLayout(3, 4)


Layout and Layout ManagersResizing GridLayout frame


Layout and Layout ManagersGridLayout example

class GridLayoutExample extends Frame{ // Constructor public GridLayoutExample() { // Call the constructor for the Frame class with the title // for the window super("GridLayout Example");

// Choose the layout manager and initialize it setLayout(new GridLayout(3, 4));

// Put components on the frame add(new Button("1")); add(new Button("2")); add(new Button("3")); add(new Button("4")); add(new Button("5")); add(new Button("6")); add(new Button("7")); add(new Button("8")); add(new Button("9")); add(new Button("0"));

// Set the size for the frame and display it pack(); show(); }}


ComponentsComponent: controls that appear on frame

ButtonsLabelsListsText fieldsOthers

Uses of componentsDisplay information (labels)Collect information (text fields, lists)Control program (buttons, menus)


Components: LabelLabel component: put text on frame

class LabelExample extends Frame{ // Constructor public LabelExample() { // Call the constructor for the Frame class with the title // for the window super("Label Example");

// Choose the layout manager and initialize it setLayout(new FlowLayout(FlowLayout.LEFT));

// Put components on the frame add(new Label("First name: ")); add(new TextField(10)); add(new Label("Last name: ")); add(new TextField(15)); add(new Label("Major: ")); add(new TextField("Computer Science"));



Components: ButtonButton component: give user control

Put on frame same as any other componentMust also tell program what to do when button pressed

Event-driven programmingProgram responds to events (such as button pushes)Older style: program has complete control

To connect event (button push) to actionDefine listener object, link to buttonListener object responds when button pushedSame listener object can handle several events

Listener object for button pushesMust be from class that implements ActionListenerMust have actionPerformed() method


Components: ButtonExample with one button

Will have Listener object be the same as the frame (With larger programs, better to separate Listener from

the frame)import java.awt.*;import java.awt.event.*;

class ButtonExample extends Frame implements ActionListener{ ...}

Define the button, assign to variableButton myButton = new Button("Press Me!");

Need the variable, so can link the button to the listener in the constructor (next slide)

Necessary forbuttons


Components: ButtonExample with one button (continued)

Constructor puts button on frame, links to listener (which is this object)

// Constructorpublic ButtonExample(){ // Call the constructor for the Frame class with the title // for the window super("Button Example");


// Put components on the frame add(myButton, BorderLayout.CENTER);

// Register the button with its listener object myButton.addActionListener(this);

// Set the size for the frame and display it setSize(200, 100); show();}

Link button tolistener


Components: ButtonExample with one button (continued)

Write actionPerformed() method in this classactionPerformed() responds when button pushed

// actionPerformed: Display "Button pressed" in the command when the// window user pressed the button.public void actionPerformed(ActionEvent event){ System.out.println("Button pressed");}

actionPerformed() method can do anything when button pushedOpen or close fileDisplay a messageQuit the program ...


Components: Buttonclass ButtonExample extends Frame implements ActionListener{ Button myButton = new Button("Press Me!");

// Constructor public ButtonExample() { // Call the constructor for the Frame class with the title // for the window super("Button Example");


// Put components on the frame add(myButton, BorderLayout.CENTER);

// Register the button with its listener object myButton.addActionListener(this);

// Set the size for the frame and display it setSize(200, 100); show(); }

// actionPerformed: Display "Button pressed" in the command // window when the user presses the button public void actionPerformed(ActionEvent event) { System.out.println("Button pressed"); }}

Button pressedButton pressedButton pressed


Components: More than 1 ButtonWhen more than one button

Each button has its own listener, orOne listener can handle several buttons

If one listener & several buttonsListener must be able to tell which button was pressedListener can use getSource() method -- returns component

that caused the event// actionPerformed: Distinguish between yesButton and noButton, and// display a corresponding message in the command// window for eachpublic void actionPerformed(ActionEvent event){ if (event.getSource() == yesButton) { System.out.println("You pressed yes"); } else { System.out.println("You pressed no"); }}


Components: More than 1 Button// Demonstrates one way to distinguish between two buttons in an// actionPerformed() method

import java.awt.*;import java.awt.event.*;

class TwoButtonsExample extends Frame implements ActionListener{ Button yesButton = new Button("Yes"); Button noButton = new Button("No"); Label myLabel = new Label();

// Constructor public TwoButtonsExample() { // Call the constructor for the Frame class with the title // for the window super("Two Button Example");


// Put components on the frame add(yesButton, BorderLayout.WEST); add(noButton, BorderLayout.EAST); add(myLabel, BorderLayout.SOUTH);

// Register the buttons with the listener object yesButton.addActionListener(this); noButton.addActionListener(this);



Components: More than 1 Button // actionPerformed: Distinguish between yesButton and noButton, // and display a corresponding message for each public void actionPerformed(ActionEvent event) { if (event.getSource() == yesButton) { myLabel.setText("You pressed yes"); } else { myLabel.setText("You pressed no"); } }}

public class DemonstrateTwoButtons{ static public void main(String[] args) { new TwoButtonsExample(); }}


Components: CheckboxCheckbox good for getting yes/no responses

Often used for option dialogsExample from JBuilder

Each checkbox can be independent of others, or can be linked to others


Components: Checkbox// Demonstration of how to use check box components.


class CheckBoxExample extends Frame implements ActionListener{ Checkbox airCondCheckBox = new Checkbox("A/C"); Checkbox cruiseCheckBox = new Checkbox("Cruise"); Button costButton = new Button("Compute Cost"); Label costLabel = new Label();

// Constructor CheckBoxExample() { // Call the constructor for the Frame class with the title // for the window super("Car Cost");


// Put components on the frame add(airCondCheckBox); add(cruiseCheckBox); add(costButton); add(costLabel);

// Register the buttons with the listener object costButton.addActionListener(this);



Components: Checkbox // actionPerformed: Compute the cost of the automobile based // on the options the user has selected public void actionPerformed(ActionEvent event) { double cost = 15000.0; if (cruiseCheckBox.getState()) { cost = cost + 1000.0; } if (airCondCheckBox.getState()) { cost = cost + 1500.0; } costLabel.setText("Cost: " + cost); }}

public class DemonstrateCheckBox{ static public void main(String[] args) { new CheckBoxExample(); }}


Components: CheckboxCheckbox groups

Can make a group of checkboxes mutually exclusive

If user clicks one, the othersgo blank

Often called “radio buttons”in other developmentenvironments

To put checkbox object in checkbox groupMake a CheckBoxGroup objectUse CheckboxGroup object in Checkbox constructor


Components: CheckboxExample

Have CheckBoxGroup paymentGroupPut cash CheckBox component into that group

Checkbox cashCheckBox = new Checkbox("Cash", false, paymentGroup);

Checkbox constructor argumentsDescriptive text string true if that checkbox should be checked by defaultCheckBoxGroup object


Components: Checkbox// Demonstration of how to use a check box group// for mutually exclusive check box components


class CheckBoxExample extends Frame implements ActionListener{ TextField amountTextField = new TextField(10); CheckboxGroup paymentGroup = new CheckboxGroup(); Checkbox cashCheckBox = new Checkbox("Cash", false, paymentGroup); Checkbox checkCheckBox = new Checkbox("Check", false, paymentGroup); Checkbox creditCardCheckBox = new Checkbox("Credit card", false, paymentGroup); Button makePaymentButton = new Button("Make payment");


Components: Checkbox // Constructor public CheckBoxExample() { // Call the constructor for the Frame class with the title // for the window super("Payment");


// Put components on the frame add(new Label("Amount")); add(amountTextField); add(new Label("Payment type")); add(cashCheckBox); add(new Label()); add(checkCheckBox); add(new Label()); add(creditCardCheckBox); add(makePaymentButton);

// Register the button with the listener object makePaymentButton.addActionListener(this);



Components: Checkbox // actionPerformed: Compute the cost of the automobile based // on the options the user has selected public void actionPerformed(ActionEvent event) { if (cashCheckBox.getState()) { System.out.println("Cash payment"); } if (checkCheckBox.getState()) { System.out.println("Check payment"); } if (creditCardCheckBox.getState()) { System.out.println("Credit card payment"); } }}

public class DemonstrateCheckBoxGroup{ static public void main(String[] args) { new CheckBoxExample(); }}


Components: ChoiceAllows user to pick from a list that’s normally hidden

User presses arrow button to see optionsUser then clicks on desired option


Components: Choice// Demonstration of how to use a choice component

import java.awt.*;import java.awt.event.*;class ChoiceExample extends Frame implements ActionListener{ Button submitButton = new Button("Submit"); Choice browserChoice = new Choice(); Label resultLabel = new Label();

// Constructor public ChoiceExample() { // Call the constructor for the Frame class with window title super("Choice Example");


// Add choices to the choice component browserChoice.add("Netscape"); browserChoice.add("Internet Explorer"); browserChoice.add("HotJava");

// Put components on the frame add(browserChoice); add(submitButton); add(resultLabel);

// Register the button with the listener object submitButton.addActionListener(this);

// Set the size for the frame and display it pack(); show(); }


Components: Choice // actionPerformed: Display the selected browser name from // the choice component public void actionPerformed(ActionEvent event) { resultLabel.setText( browserChoice.getSelectedItem()); }}

public class DemonstrateChoice{ static public void main(String[] args) { new ChoiceExample(); }}


Components: TextFieldAllows user to type one line of text

Allows user to enter anythingRetrieve text from the field with getText() method


Components: TextField// Demonstrates the use of text field components


class TextFieldExample extends Frame implements ActionListener{ TextField firstNameText = new TextField(15); TextField lastNameText = new TextField(20); TextField majorText = new TextField("CompSci");

Button submitButton = new Button("Submit"); Label resultLabel = new Label();

// Constructor public TextFieldExample() { // Call the constructor for the Frame class with window title super("TextField Example");



Components: TextField // Put components on the frame add(new Label("First name: ")); add(firstNameText); add(new Label("Last name: ")); add(lastNameText); add(new Label("Major: ")); add(majorText); add(submitButton); add(resultLabel);

// Register the button with the listener object submitButton.addActionListener(this);


// actionPerformed: Display the first name, last name, and name // of major from the three text field areas public void actionPerformed(ActionEvent event) { resultLabel.setText(firstNameText.getText() + " " + lastNameText.getText() + " " + majorText.getText()); }}

public class DemonstrateTextField{ static public void main(String[] args) { new TextFieldExample(); }}


Components: TextAreaLike TextField, but allows user to type more than

one line


Components: TextArea// Demonstration of a TextArea component

import java.awt.*;import java.awt.event.*;class TextAreaExample extends Frame implements ActionListener{ TextArea nameAndAddressTextArea = new TextArea(); Button submitButton = new Button("Submit");

// Constructor public TextAreaExample() { // Call the constructor for the Frame class with window title super("TextArea Example");


// Put components on the frame add(new Label("Name and address"), BorderLayout.WEST); add(nameAndAddressTextArea, BorderLayout.CENTER); add(submitButton, BorderLayout.SOUTH);


Components: TextArea // Register the button with the listener object submitButton.addActionListener(this);


// actionPerformed: Display the contents of the TextArea // component in the command window public void actionPerformed(ActionEvent event) { System.out.println(nameAndAddressTextArea.getText()); }}

public class DemonstrateTextArea{ static public void main(String[] args) { new TextAreaExample(); }}


Components: TextAreaTextArea methods

Method Parameters Description

append() String Append the string to the end of the text in thetext area.

getText() none Return the contents of the text area as a string.

insert() String, int Insert the string into the text in the text areastarting at the given position (position starts at 0in the text).

setText() String Change the contents of the text area to the givenstring.

replaceRange() String, int, int Replace text in the text area between the givenpositions.


Components: TextAreaExample of using TextArea methods


Components: TextArea// Demonstration of the append(), insert(), and// replaceRange() methods of the TextArea class.

import java.awt.*;import java.awt.event.*;import java.text.*;

class TextAreaExample2 extends Frame implements ActionListener{ TextArea aTextArea = new TextArea(); TextField someTextTextField = new TextField(30); TextField firstPositionTextField = new TextField(); TextField secondPositionTextField = new TextField(); Button insertButton = new Button("Insert"); Button appendButton = new Button("Append"); Button replaceButton = new Button("Replace"); Button exitButton = new Button("Exit");


Components: TextArea // Constructor public TextAreaExample2() { // Call the constructor for the Frame class with the title // for the window super("TextArea Example");


// Make a panel for data entry and buttons Panel controlPanel = new Panel(new GridLayout(5, 2));

// Put control components on the panel controlPanel.add(new Label("Text")); controlPanel.add(someTextTextField); controlPanel.add(new Label("Position 1")); controlPanel.add(firstPositionTextField); controlPanel.add(new Label("Position 2")); controlPanel.add(secondPositionTextField); controlPanel.add(insertButton); controlPanel.add(appendButton); controlPanel.add(replaceButton); controlPanel.add(exitButton);


Components: TextArea // Put components on the frame add(aTextArea, BorderLayout.CENTER); add(controlPanel, BorderLayout.SOUTH);

// Register the buttons with the listener object insertButton.addActionListener(this); appendButton.addActionListener(this); replaceButton.addActionListener(this); exitButton.addActionListener(this);


// actionPerformed: Handle the event for the associated button // press public void actionPerformed(ActionEvent event) { // Close the program if exitButton pressed if (event.getSource() == exitButton) { setVisible(false); dispose(); System.exit(0); }


Components: TextArea // Replace aTextArea between the positions given in // firstPosition and secondPosition with the contents of // someTextTextField else { // Convert the number in the secondPosition text field // to an integer int secondPosition = formatter.parse( secondPositionTextField.getText()).intValue(); aTextArea.replaceRange( someTextTextField.getText(), firstPosition, secondPosition); } }

// Ignore any ParseExceptions catch (ParseException e) {} } }}

public class DemonstrateTextArea2{ static public void main(String[] args) { new TextAreaExample2(); }}


PanelPanel

Container that can hold other compoents (including panels)

Like a miniature frame -- can put components on it, but no title or border

Can put panel on a frame, then put other components in the panel

One frame can have several panelsEach panel can have its own layout manager, which can

be different from frame’s layout manager


PanelTwo panels on a BorderLayout frame

F ra m e isB o rd e rL a yo u t

T o p p a n e l isG r id L a yo u t

B o tto m p a n e lis F lo wL a yo u t


Panel// Demonstration of how to use panels

import java.awt.*;

class PanelExample extends Frame{ public PanelExample() { // Constructor super("Panel Example");

// Define a panel for the South area, and add its button // components Panel buttonPanel = new Panel(new FlowLayout()); buttonPanel.add(new Button("Mail")); buttonPanel.add(new Button("News")); buttonPanel.add(new Button("WWW"));

// Define a panel for the North area, and add its label and // text field components Panel loginPanel = new Panel(new GridLayout(2, 2)); loginPanel.add(new Label("Login: ")); loginPanel.add(new TextField(15)); loginPanel.add(new Label("Password: ")); loginPanel.add(new TextField("********"));

// Choose the layout manager for the frame and initialize it setLayout(new BorderLayout());


Panel

// Put components on the frame add(loginPanel, BorderLayout.NORTH); add(new TextArea(), BorderLayout.CENTER); add(buttonPanel, BorderLayout.SOUTH);


public class DemonstratePanel{ static public void main(String[] args) { new PanelExample(); }}


MenusCommon feature in most GUI programs

Program can have many commands, arranged hierarchically

Menu doesn’t take much screen space


MenusHow to make a menu

Make a MenuBar object, add to frameMenuBar mb = new MenuBar();setMenuBar(mb);

Make top-level Menu objects, add to MenuBar objectMenu fileMenu = new Menu("File");mb.add(fileMenu);

Make MenuItem objects, add to Menu objectMenuItem openMenuItem = new MenuItem("Open");fileMenu.add(openMenuItem);

Add listener object to each MenuItem objectexitMenuItem.addActionListener(this);


Menus// Demonstration of menus (also shows the// recommended way to exit a Java GUI application)


class MenuExample extends Frame implements ActionListener{ Menu fileMenu = new Menu("File"); Menu editMenu = new Menu("Edit"); MenuItem openMenuItem = new MenuItem("Open"); MenuItem saveMenuItem = new MenuItem("Save"); MenuItem exitMenuItem = new MenuItem("Exit"); MenuItem copyMenuItem = new MenuItem("Copy"); MenuItem cutMenuItem = new MenuItem("Cut"); MenuItem pasteMenuItem = new MenuItem("Paste");


Menus // Constructor public MenuExample() { // Call the constructor for the Frame class with the title // for the window super("Menu Example");


// Define a menu bar object and add it to frame MenuBar mb = new MenuBar(); setMenuBar(mb);

// Add menus to menu bar mb.add(fileMenu); mb.add(editMenu);

// Add menu items to menus fileMenu.add(openMenuItem); fileMenu.add(saveMenuItem); fileMenu.addSeparator(); fileMenu.add(exitMenuItem); editMenu.add(copyMenuItem); editMenu.add(cutMenuItem); editMenu.add(pasteMenuItem);

// Add listener for menu items exitMenuItem.addActionListener(this); // (add others here ...)



Menus // actionPerformed: Handle events for the menu. This example // only shows how to handle the exit menu // item. Other menu items could be handled // in a similar way. public void actionPerformed(ActionEvent event) { if (event.getSource() == exitMenuItem) { setVisible(false); dispose(); System.exit(0); } }}

public class DemonstrateMenu{ static public void main(String[] args) { new MenuExample(); }}


FileDialogUse FileDialog to open, save files

Purpose: Get file name from userWindows “Open” file dialog


FileDialogPlatform independent

Uses native dialog for computer running programWindows “Save As” file dialog


FileDialogHow to use FileDialog to get file name from user

Make a FileDialog objectFileDialog openDialog = new FileDialog(this, "Open", FileDialog.LOAD);

•First parameter: parent frame (waits while dialog displayed)•Second parameter: title on dialog•Third parameter: FileDialog.OPEN or FileDialog.SAVE

Display the dialog// Display the dialog and get the filename from the useropenDialog.setVisible(true);

Hide the dialog after user picks a file// Hide the dialog so it does not cover the application,// but is still available so we can get the filenameopenDialog.setVisible(false);

•Don’t delete or dispose of dialog until after getting file name


FileDialogGet filename with getFile(), getDirectory()

// Check whether user canceled the loadif (openDialog.getFile() == null){ System.out.println("User canceled the load");}else{ // Display the full filename in the command window System.out.println("Open file " + openDialog.getDirectory() + openDialog.getFile());}

Can dispose of dialog, garbage collect it, or leave hidden// Optional stepopenDialog.dispose();

Directory and file names vary between platformsWindows: c:\My Documents\Programs\Program1.javaUnix: /usr/users/smith/programs/Program1.javaVAX: [smith.programs]Program1.java


FileDialogExample Program


FileDialog// Demonstrates the use of FileDialog

import java.io.*;import java.awt.*;import java.awt.event.*;

class FileDialogExample extends Frame implements ActionListener{ // Interface variables Button openButton = new Button("Open"); Button saveButton = new Button("Save");

// Constructor public FileDialogExample() { // Call the constructor for the Frame class with the title // for the window super("FileDialog Example");


// Add components to frame add(openButton); add(saveButton);


FileDialog // Add listener for buttons openButton.addActionListener(this); saveButton.addActionListener(this);


// actionPerformed: Detect the event (Open, or Save) // display either a load file dialog or a // save file dialog. Display the name of the // file that the user has selected in the // command window. public void actionPerformed(ActionEvent event) { if (event.getSource() == openButton) { FileDialog openDialog = new FileDialog(this, "Open", FileDialog.LOAD);

// Display the dialog and get the filename from the user openDialog.setVisible(true);

// Hide the dialog so it does not cover the application, // but is still available so we can get the filename openDialog.setVisible(false);


FileDialog // Check whether user canceled the load if (openDialog.getFile() == null) { System.out.println("User canceled the load"); } else { // Display the full filename in the command window System.out.println("Open file " + openDialog.getDirectory() + openDialog.getFile()); } } else if (event.getSource() == saveButton) { FileDialog saveDialog = new FileDialog(this, "Save", FileDialog.SAVE);

// Display the dialog and get the filename from the user saveDialog.setVisible(true);

// Hide the dialog so it does not cover the application, // but is still available so we can get the filename saveDialog.setVisible(false);


FileDialog // Check whether user canceled the save if (saveDialog.getFile() == null) { System.out.println("User canceled the save"); } else { // Display the full filename in the command window System.out.println("Save file " + saveDialog.getDirectory() + saveDialog.getFile()); } } }}

public class DemonstrateFileDialog{ static public void main(String[] args) { new FileDialogExample(); }}


SimpleEditorDesign a simple editor around FileDialog and

TextAreaCan only open and

save files -- no cut, copy, paste (except using keyboard commands)

Has a toolbar forfrequent commands

Also has a menusystem


SimpleEditor// This program is a simple editor that allows// the user to type in text and save it to a file. The user// can also load text from a file.//// The program has one menu with menu items Open, Save, and// Exit. It also has a "toolbar" across the top with buttons// for Open, Save, and Exit.//// It is a simple demonstration of TextArea, menus, and// file dialogs.

import java.io.*;import java.awt.*;import java.awt.event.*;

public class SimpleEditor extends Frame implements ActionListener{ // Interface variables Menu fileMenu = new Menu("File"); MenuItem openMenuItem = new MenuItem("Open"); MenuItem saveMenuItem = new MenuItem("Save"); MenuItem exitMenuItem = new MenuItem("Exit"); Button openButton = new Button("Open"); Button saveButton = new Button("Save"); Button exitButton = new Button("Exit"); TextArea editTextArea = new TextArea();


SimpleEditor // Constructor public SimpleEditor() { // Call the constructor for the Frame class with the title // for the window super("Simple Editor");


// Define a menu bar object and add it to frame MenuBar mb = new MenuBar(); setMenuBar(mb);

// Add menu to menu bar mb.add(fileMenu);

// Add menu items to menu fileMenu.add(openMenuItem); fileMenu.add(saveMenuItem); fileMenu.addSeparator(); fileMenu.add(exitMenuItem);


SimpleEditor // Add listener for menu items openMenuItem.addActionListener(this); saveMenuItem.addActionListener(this); exitMenuItem.addActionListener(this);

// Make a "toolbar" panel out of the three buttons Panel toolbarPanel = new Panel(); toolbarPanel.setLayout(new FlowLayout(FlowLayout.LEFT)); toolbarPanel.add(openButton); toolbarPanel.add(saveButton); toolbarPanel.add(exitButton);

// Add listener for buttons openButton.addActionListener(this); saveButton.addActionListener(this); exitButton.addActionListener(this);

// Add components to frame add(toolbarPanel, BorderLayout.NORTH); add(editTextArea, BorderLayout.CENTER);

// Set the size for the frame and display // it setSize(300, 300); show(); }


SimpleEditor // actionPerformed: Detect the event (Open, Save, or Exit) // and handle the event. The Exit event is // handled within the method. The Open and // Save events are delegated to other // private methods in this class. public void actionPerformed(ActionEvent event) { if (event.getSource() == exitMenuItem || event.getSource() == exitButton) { setVisible(false); dispose(); System.exit(0); } else if (event.getSource() == openMenuItem || event.getSource() == openButton) { readTextFromFile(); } else if (event.getSource() == saveMenuItem || event.getSource() == saveButton) { saveTextToFile(); } }


SimpleEditor // readTextFromFile: Ask the user for a filename, then open the file // and read its contents into the TextArea edit buffer. private void readTextFromFile() { try { // Initialize the file variable File inFile = new File(getLoadFileName());

// Create an input stream and attach it to the file BufferedReader fileInStream = new BufferedReader(new FileReader(inFile));

// Read from the file editTextArea.setText(""); String line = fileInStream.readLine(); while (line != null) { editTextArea.append(line + '\n'); line = fileInStream.readLine(); }

// Close the stream fileInStream.close(); } catch (java.io.IOException e) {} }


SimpleEditor // saveTextToFile: Ask the user for a filename, then save the // contents of the TextArea edit buffer. // NOTE: This method saves the text with just linefeeds between // lines. Some programs require a carriage return along // with each line feed between lines so they can read the // file. This is common with Windows 95/98/NT programs. private void saveTextToFile() { try { // Initialize the output file variable File outFile = new File(getSaveFileName());

// Create a buffered output stream, wrapped by // PrintWriter, and attach it to the file PrintWriter fileOutStream = new PrintWriter(new BufferedWriter (new FileWriter(outFile)));

// Write the output to the file fileOutStream.println(editTextArea.getText());

// Close the output stream fileOutStream.close(); } catch (java.io.IOException e) {} }


SimpleEditor // getLoadFileName: Display a file dialog for loading a file. // Return the full name of the file. private String getLoadFileName() { FileDialog openDialog = new FileDialog(this, "Open", FileDialog.LOAD);

// Display the dialog and get the filename from the user openDialog.setVisible(true);

// Hide the dialog so it does not cover the application, // but is still available so we can get the filename openDialog.setVisible(false);

// Return the full filename return openDialog.getDirectory() + openDialog.getFile(); }


SimpleEditor // getSaveFileName: Display a file dialog for saving a file. // Return the full name of the file. private String getSaveFileName() { FileDialog saveDialog = new FileDialog(this, "Save", FileDialog.SAVE);

// Display the dialog and get the filename from the user saveDialog.setVisible(true);

// Hide the dialog so it does not cover the application, // but is still available so we can get the filename saveDialog.setVisible(false);

// Return the full filename return saveDialog.getDirectory() + saveDialog.getFile(); }

// main: Run an instance of the SimpleEditor // class. // NOTE: This technique of putting main () inside // the application class, rather than making a // separate class for it, is commonly used, // especially for testing classes. static public void main(String[] args) { new SimpleEditor(); }}


Other Capabilities of AWTOther layout managers

CardLayout GridBagLayout

Scroll barsText formatting

Fonts Styles Weights Colors

Nested menus (submenus)

Other dialogs Confirmation of exit

Other listeners Keyboard presses Mouse movements Mouse clicks Changes to text

Can extend Layout managers Components

Many other features!


Swing ComponentsJava 2 introduces Swing components, with

Pluggable look and feel: Microsoft Windows, Motif, Java, and others

Accessibility: designed for convertion into textual forms for screen readers (makes GUI programs more accessible to visually-impaired users)

Drag and drop: allow user to drag information from Java programs to other programs

Many more components


Swing ComponentsSwing largely a superset of AWT

Most AWT components have counterparts in SwingSwing versions start with J, (JLabel, JButton, ...)

Doesn’t include layout managers or listenersMust use AWT versions of these

Example


Swing ComponentsImport AWT and

Swingimport java.awt.*;import java.awt.event.*;import javax.swing.*;

Extend JFrameclass SwingExample extends JFrame implements ActionListener{}

Define Swing componentsJTextField firstNameTextField = new JTextField(20);JTextField lastNameTextField = new JTextField(20);JLabel fullNameLabel = new JLabel();JButton submitButton = new JButton("Press Me!");


Swing ComponentsConstructor

// Constructorpublic SwingExample(){ // Call the constructor for the JFrame class with the title // for the window super("Swing Example");

// Get content pane for this frame Container contentPane = getContentPane();

// Choose the layout manager and initialize it contentPane.setLayout(new GridLayout(3, 2));

// Put components on the frame contentPane.add(new Label("First name: ")); contentPane.add(firstNameTextField); contentPane.add(new Label("Last name: ")); contentPane.add(lastNameTextField); contentPane.add(submitButton); contentPane.add(fullNameLabel);

// Register the button with its listener object submitButton.addActionListener(this); // Set the size for the frame and display it pack(); show();}

Add componentsto content pane

Create content pane


Swing ComponentsactionPerformed()

method

// actionPerformed: Display "Button pressed" in the command // window when the user pressed the button public void actionPerformed(ActionEvent event) { fullNameLabel.setText(firstNameTextField.getText() + " " + lastNameTextField.getText()); }

Same as AWT version


Swing ComponentsUse Swing components largely like AWTSwing components more flexible

Can make a round Swing buttonCan put an image on a button

GotchasDon’t mix AWT and Swing components -- AWT will

probably cover up Swing componentsDon’t put Swing components on a Frame -- use JFrameModify Swing components only in event handlers

(actionPerformed(), ...)

Date post:	17-Jan-2016
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