Chapter 3: Widgets for a GUI General Component methods Useful widgets classes –Text classes Label TextField TextArea –Active widgets Button Checkbox Choice List

Building a GUI Graphical User Interfaces composed of widgets (buttons, text fields, etc.) Various useful classes defined in AWT Part of Component class (abstract class)

Component methods (inherited by all): Point location() - x,y position Dimension size() - width,height of object Rectangle bounds() - both location, size info void move (int x, int y) - set x,y position void resize (int w, int h) - set w,h of object void resize (Dimension d) - similar void reshape (int x, int y, int w, int h) - set rectangle Dimension minimumSize() - determined by system, smallest size needed Dimension preferredSize() - similar to minimum

Component methods (cont): Color getBackground() - return background color Color getForeground() - return foreground color void setBackground(Color c) - set background color void setForeground(Color c) - set foreground color Font getFont() - return current font void setFont(Font f) - set current font boolean isShowing() - true if Component on screen boolean isVisible() - true if object should be visible void hide() - turns component invisible void show() - makes component visible

Component methods (cont): Graphics getGraphics() - returns the Graphics object associated with the current component, useful for doing graphical operations on this component void paint(Graphics g) - method that “shows” component, should not be called by user (overridden) void repaint() - informs the computer that this component needs to be repainted void repaint(int x, int y, int width, int height) - similar to repaint() but indicates only the portion falling in the rectangle needs to be redone void update(Graphics g) - how component redone (generally box erased, repainted), useful to avoid flicker, should not be called by user (overridden)

Text Classes Label - simple text statements, generally one line with no editing expected TextComponent - abstract class with methods used by –TextField - one line text, with some editing –TextArea - generally for more than one line of text with some editing

Label class constructors: Label() - no text, center alignment Label(String label) - center-aligned label with text Label(String label, int alignment) - label with text aligned based on arg, vals: Label.LEFT, CENTER, RIGHT methods: String getText() - return string associated with Label void setText(String label) - set string int getAlignment() - return Label’s current alignment void setAlignment(int alignment) - set alignment

TextComponent class abstract class (parent of TextField, TextArea) methods: String getText() - return the text associated with object void setText(String text) - set text of object boolean isEditable() - flag indicating text can be edited void setEditable(boolean canEdit) - set editable flag String getSelectedText() - return highlighted text int getSelectionStart() - location where selection starts int getSelectionEnd() - location where selection ends void select (int start, int end) - select text start-end void selectAll() - select all of text

TextField class - one line, editing constructors: TextField() - empty (no text), default (system) width TextField(int columns) - no text, columns wide TextField(String text) - set text, use it for width TextField(String text, int columns) - set text, width methods: int getColumns() - return column width of object void setColumns(int c) - set column width char getEchoChar() - return echo char (if any) void setEchoChar(char c) - set echo char boolean echoCharIsSet() - check if echo char set Dimension minimumSize() - minimum needed size Dimension preferredSize() - preferred size

TextArea class - > 1 line, editing look and feel depends on system (may include scrollbars) constructors: TextArea() - empty (no text), default (system) size TextArea(int rows, int cols) - no text, rows, cols size TextArea(String text) - set text, default sized TextField(String text, int rows, int cols) - set text, size methods: int getColumns() - column width of object int getRows() - row height of object

TextArea class (cont) methods: void appendText(String str) - add string to the end of the current text void insertText(String str, int pos) - insert string at position pos void replaceText(String str, int start, int end) - insert string replacing chars from start to end Dimension minimumSize() - minimum required size Dimension preferredSize() - preferred size

import java.applet.*; import java.awt.*; public class TestClass extends Applet { Label myLabel1 = new Label("Test label 1",Label.LEFT); Label myLabel2 = new Label(); TextField myTextField1 = new TextField("Init text",20); TextField myTextField2 = new TextField("Start text"); TextArea myTextArea = new TextArea("Initial text",3,10); public void init () { resize(500,400); myLabel1.setText("TLab1"); myLabel2.setText("TLab2"); myTextField1.setForeground(Color.green); myTextField2.setEchoCharacter('*'); myTextArea.insertText("silly ",8); add(myLabel1); add(myTextField1); add(myTextArea); add(myLabel2); add(myTextField2); }

Active Widgets Various classes provide mechanisms for users to indicate info: –Button - labeled object that can be clicked –Checkbox - labeled object, can be checked/un –Choice - object providing multiple choices with one showing –List - object providing multiple choices with all showing

Button class constructors: Button() - unlabeled button Button(String label) - button with label methods: String getLabel() - return label of object void setLabel(String label) - set label of Button We will learn later how to check if the mouse has been used to access button

Checkbox class constructors: Checkbox() - no label, initially unchecked Checkbox(String label) - labeled, initially unchecked Checkbox(String label, CheckboxGroup group, boolean state) * methods: String getLabel() - return label of object void setLabel(String label) - set label of Checkbox boolean getState() - determine if checked/unchecked void setState(boolean state) - set the state of the Checkbox CheckboxGroup getCheckboxGroup() - returns group *

CheckboxGroup class Checkbox objects added using Checkbox methods constructors: CheckBoxGroup() - empty group methods: Checkbox getCurrent() - Checkbox of group that is checked void setCurrent(Checkbox c) - set c as checked member

import java.applet.*; import java.awt.*; public class TestButton extends Applet { Button myButton = new Button("AButton"); Checkbox myCheckBox1 = new Checkbox("CB1"); Checkbox myCheckBox2 = new Checkbox("CB2"); CheckboxGroup myCheckBoxGroup = new CheckboxGroup(); Checkbox myCBG1 = new Checkbox("Big"); Checkbox myCBG2 = new Checkbox("Bigger"); Checkbox myCBG3 = new Checkbox("Biggest"); public void init () { resize(500,400); myCheckBox2.setState(true); myCBG1.setCheckboxGroup(myCheckBoxGroup); myCBG2.setCheckboxGroup(myCheckBoxGroup); myCBG3.setCheckboxGroup(myCheckBoxGroup); myCheckBoxGroup.setCurrent(myCBG1); add(myCheckBox1); add(myButton); add(myCBG1); add(myCBG2); add(myCBG3); add(myCheckBox2); }

Choice class constructor: Choice() - initially empty set of choices methods: void addItem(String item) - add the named item to the choices int getSelectedIndex() - return num of selected item String getSelectedItem() - return string associated with item String getItem(int index) - returns string of index item void select(int index) - select the index item (starting at 0) void select(String item) - select item with string name int countItems() - return number of items

List class constructors: List() - default-size list in single-selection mode List(int rows, boolean multSel) - list with rows, if multSel true can make multiple selections methods: void addItem(String item) - add the named item to the choices void addItem(String item, int index) - add item at loc index void delItem(int index) - remove the index item void delItems(int start, int end) - remove items from start to end void clear() - remove all items void replaceItem(String item, int index) - replace item at index int countItems() - count of the number of items in List

methods: void getSelectedIndex() - num of selected index -1 if multiple or none boolean isSelected(int index) - true if index selected void select(int index) - set index as selected void deselect(int index) - unselect index void makeVisible(int index) - scroll so index visible int getVisibleIndex() - index of last makeVisible call boolean allowsMultipleSelections() - true if list allows multiple selections void setMultipleSelections(boolean m) - set multiple selection flag to m

methods: int getRows() - number of rows in object Dimension minimumSize() - min size needed Dimension minimumSize(int rows) - min size for rows Dimension preferredSize() - preferred size Dimension preferredSize(int rows) - preferred by rows

import java.applet.*; import java.awt.*; public class TestLists extends Applet { Choice myChoice = new Choice(); List myList = new List(4,true); public void init () { resize(500,400); myChoice.addItem("Small"); myChoice.addItem("Medium"); myChoice.addItem("Large"); myChoice.select("Medium"); myList.addItem("Left"); myList.addItem("Right"); myList.addItem("Straight"); myList.select(0); myList.select(2); add(myChoice); add(myList); }