copyright © 2008-2015 curt hill first window builder program easy guis in eclipse

Copyright © 2008-2015 Curt Hill

First Window Builder Program

Easy GUIs in Eclipse

Preliminaries• Goal: Create a Windows program

using Eclipse with the Window Builder plugin

• The problem to solve is to take the number of years and convert it into the number of seconds of a persons life

• Simple GUI with:– Two buttons– One input– One output


Disclaimer• There is a lot to know• So we have much to cover• Fortunately, it is easier than it

might seem• We will follow with a

demonstration• We will have more presentations to

further explain things


Needed Objects• JFrame

– A window and container

• JButton• JTextField

– A field to type in data

• JLabel• LayoutManager

– Organizes GUI objects in a container– Handles the resizing

• ListenersCopyright © 2008-2015 Curt Hill

Process• First we do the normal things:• Start Eclipse

– The Window Builder plugin should have been previously installed

• Close all open projects• Create a new project

– We do not create the new Java class

• This is where it starts to change• We add a Windows application• We do this with dropdown menu


Add an Application Window


Fill in Package and Name


After Finish Clicked


What do we have?• A program with 44 lines• 3 methods

– Main– initialize– NewWindow

• We are not yet ready to modify the Java code

• Notice at the bottom of the code there are two tabs– Source and design


Looking at Source


Now Click on Design


Commentary• On the right is a stylized preview of

what the window will look like• The middle pane describes

components we can drag onto the window

• On lower left is property inspector• First we will change the window

characteristics• We click on the window in the right

pane • Scroll down to title and type


Add a title


If we run we get


Click Flow and Drag


Adding Components• We click on items and then drag

over to window• First start with a Jlabel• Click it• Click in the Window


Jlabel Added


Change Contents• After we drop it, it should be

selected in the property inspector• Change the Text property to Years


Text Property Changed


Next• We are now up to 51 lines and

have coded nothing• The next thing to do is add the

input box• This is the Java JTextField• Similar to the JLabel as far as

adding• Also similar to JLabel for setting

the original value• It may precede or follow the label


JTextField Dragging


Setting Text


Buttons• The slightly harder one is buttons• They have the same drag, set

value as JLabels and JTextAreas• They also need an event handler• Even that is not hard• We must show the events


Button Placed


Show Events Clicked


Scroll Down and Opened


Action• When you double click on the

Mouse Clicked slot it generates an event handler

• The event handler is method that is called when the event occurs

• It then takes you to the code page• The event handler is called

mouseClicked• It is preceded by an annotation

@overrideCopyright © 2008-2015 Curt Hill

Code


Event Handler• The event handler is now an empty

method in the initialized method• Now we have to make that method

do something• Many programs and event

handlers have this basic form:// Get data// Do computations// Display results


Getting Data• The main problem is that a textfield

always has type String text in it• If we are interested in numerics

then we must convert the String to a number

• This is done with static methods of a wrapper class– Usually Integer.parseInteger or

Double.parseDouble

• We cannot use Scanner– That is console/file based


TextField to Numerics• To convert an edit box value to a

usable numeric value, we use the wrapper classes– Integer– Double

• A wrapper class makes a class out of a primitive

• Then it gives static methods that are useful for that primitive

• Today we want parseInt from Integer or parseDouble from Double


Conversion• We can use this:

String val = textField.getText();int v = Integer.parseInt(val);

• Or combine into one:int i = Integer.parseInt(edit1.getText());double d = Double.parseDouble(edit1.getText());

• This causes the value to be obtained from the edit box named edit1 and converted into an int or double


Back to a String• To display a result in either a

JTextField or JLabel requires the setText method

• This may only take a String• There is no String constructor that

takes a numeric• There is however the valueOf method• Thus:lab1.setText( String.valueOf(d));


Another Conversion• You may also concatenate a

number to a string painlessly:int a = b*c/2;String s = “Answer: “+a;

• However, you may not assign a number to a string directly without valueOfs = a; // Illegals = String.valueOf(a); // OK


Static Methods• parseInt, parseDouble, and valueOf

are all static methods• A static method does not need an

instance of the type• We usually use the class name as

if it were an instance:Integer.parseInt(x);Double.parseDouble(y);String.valueOf(u);


Casts• Why do we not cast these

conversions?• Casts only work on primitive types• A String is not a primitive so it

must use a static method to convert values into it

• Similarly the wrapper methods also use static methods to make a double out of a string


Get Data• The data is in the text field named text

• The method call:text.getText() will get it

• Then we convert into an integer with:Integer.parseInt(…)

• We use:int years = Integer.parseInt( text.getText());


Do Computations• The computation is merely a bunch

of multiplications to convert years into seconds

• Multiply by– Days in year– Hours in day– Minutes in an hour– Seconds in a minutedouble sec = years*365.25*24*60*60;


Display Results• System.out.println is used for

console programs• In a GUI we put the result in a

Label or TextField• In this example the label is named

label• We use the setText method:

label.setText(“”+sec);


Event Handler


Are we done?• This program is now 80 lines

– Three of which we have coded

• It still needs some work:– An exit button– An about button

• However, most of that can wait until we get this part under control


New Button• Exit button is simple, add a new:

– Button– Event handler

• The event handler method should execute:System.exit(0);

• This enlarges the program to 82 lines

• The About needs a dialog which will wait for a future presentation


With Exit Button


Errors• In generating this presentation I

received an error in Windows Builder

• The program would compile and run

• So I exited Eclipse and started it and it was fine


Lastly• We are up to about 89 lines• Seven of these we coded directly

– Four Java lines– Three comment lines

• The rest Windows Builder generated

• We will next do the demo


copyright © 2008-2015 curt hill first window builder program easy guis in eclipse

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