Programming and Problem Solving with Java

CASE STUDY^415

Before we go on, let’s simplify the problem somewhat. We will first create a calcula-
tor with only plus and minus functions. After we verify this simplified version of the
application, we can add division and multiplication operations. (See Case Study Follow-
Up Exercise 10.)

The responsibility of main, creating the user interface, is similar to what we’ve done
in several previous applications. Does this mean that we can just cut and paste the
algorithms? No, the objects in the window are not the same, but the steps used to
create them are the same, so we already know how to write the outline of the
algorithm. The steps shown in color require further expansion. We’re applying
functional decomposition to simplify the problem-solving process.

Instantiate Each Interface Object

Set calcFrame to address of new JFrame

Get content pane from calcFrame and assign its address to calcPane

Set up calcPane as a four-row, two-column grid

Set resultLabel to address of new JLabel, "Result:"

Set register to address of new JLabel, "0.0"

Set inputField to address of new JTextField, empty with 10 spaces

Set add to address of new JButton, "+"

Set subtract to address of new JButton, "-"

Set clear to address of new JButton, "Clear"

public static main method (standard arguments)

Instantiate each interface object

Register listeners with buttons

Create the frame

Get the content pane

Size the frame

Set default close operation

Set layout manager for the pane

Add each interface object to the pane

Make the frame visible

Declare Interface Variables

Declare a JFrame, calcFrame

Declare a Container, calcPane

Declare a JLabel, resultLabel

Declare a JLabel, register

Declare a JLabel, entryLabel, for prompting

Declare a JTextField, inputField, for input

Declare a JButton, add

Declare a JButton, subtract

Declare a JButton, clear