Field Trip #23

HangmanBy Keith Lynn

JApplet

A JApplet is a top-level container An applet is a small Java program that is

executed by another program such as a browser

JApplet is updated version of applet that allow us to use lightweight components that don't depend heavily on their environment

This means that components should look the same no matter what environment they are on

Appletviewer

An alternative to using a browser is to use the appletviewer program that is included in the JDK

In order to use the appletviewer program, we create an HTML document where we include an applet tag

The applet tag must contain the name of the class, the width and height

JButton

A JButton is a graphical component We can place text on a JButton A JButton has a margin so some characters

won't be displayed We can change the margin by obtain an Insets

object and setting left and right to 0 and then applying it to the button

Graphics

In order to display things like graphics, we will override either the paint or paintComponent method

If we are directly drawing on a JApplet, then we override its paint method

We can also create an instance of a JPanel and add this to the JApplet

In the JPanel, we override the paintComponent method

LayoutManager

We can specify how components are added to a Japplet or Jpanel by specifying a layout manager

There are several built-in layout managers FlowLayout lays out components in a row GridLayout lays out components in a grid

String

A String is a collection of characters We can retrieve the character at a certain

location in a String with the method charAt(int) We can append characters to the String using

the + symbol We can compare two Strings using the method

equals or equalsIgnoreCase

Char

A char is a single character There is a special relationship between chars

and ints in Java If you treat a char as an int, it is converted to

the ASCII value of the char The ASCII value of 'A' is 65

Events

We can detect events and act on them by creating an event listener

An event listener we can use with a button is the ActionListener

ActionListener is an interface which contains the method actionPerformed

If an ActionListener is registered with a button, then when the button is clicked, actionPerformed is called

Drawing Lines

In order to draw lines and shapes, we need a Graphics object

We get a reference to a Graphics object by overriding paint in a heavyweight component and paintComponent in a lightweight component

A Jpanel is a lightweight component We the method drawLine(x0,y0,x1,y1) to draw a

line between (x0,y0) and (x1,y1)

Sounds

In order to play a sound in an applet, we use the method getAudioClip

The first parameter to getAudioClip is a URL This can be a URL on the web or

getCodeBase() to refer to the location of the .class file of the applet or getDocumentBase() to refer to the location of the .html file of the applet

We play the audio clip with the method play

Hangman

The plan for creating Hangman is to create three panels

The first panel will contain buttons that represent the characters in the word

The second panel will contain buttons indicating the characters in the alphabet that haven't been chosen

The third panel will be used to draw the hangman

Hangman, cont'd We attach a listener to the buttons representing

the alphabet Each time a letter is clicked, we search the

word and display occurrences of the letter We then make the letter invisible in the alphabet If the letter didn't occur, we display another part

of the hangman If the word is filled in the game is over and the

user wins If the hangman is filled in and the word isn't, the

user loses