2. Copyright © 2008-2013 Curt Hill First Windows Program GUIs in Eclipse

3. Preliminaries Goal: Create a Windows program using Eclipse 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 Copyright © 2008-2013 Curt Hill

4. Disclaimer There is a lot to know Fortunately, there are some shortcuts The presentation goes through how to do this the hard way –In most cases it will be much easier These will be shown at the end of the presentation The shortcuts will be considered in the demonstration Copyright © 2008-2013 Curt Hill

5. 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 Listeners Copyright © 2008-2013 Curt Hill

6. How does it fit? Declare and initialize controls –Such as buttons Add them to a layout manager –Controls the display and sizing Create listeners for the buttons –Listeners are separate classes The listeners call a method in the main class to handle the event Copyright © 2008-2013 Curt Hill

7. Procedure Create an Eclipse project –We have done this before Add a Java class to it –We will use JFrame as ancestral class Add the objects: –Two buttons –One textfield –One label Copyright © 2008-2013 Curt Hill

8. Create Project Copyright © 2008-2013 Curt Hill

9. Add a new Java Class 1 Copyright © 2008-2013 Curt Hill

10. Name Package and Object Copyright © 2008-2013 Curt Hill

11. Browse for a Type Copyright © 2008-2013 Curt Hill

12. Choose Object: javax.JFrame Copyright © 2008-2013 Curt Hill

13. Things to be Set Copyright © 2008-2013 Curt Hill

14. After Finish Clicked Copyright © 2008-2013 Curt Hill

15. What goes in main? Create the constructor –Constructor is method with same name as class Set the size Make the location Make it appear Copyright © 2008-2013 Curt Hill

16. Constructor The constructor will look something like this for now: public Win1(String s){ super(s); init(); } It will be called like this from main: Win1 w = new Win1(“Age in Seconds”); The call to super is to calling the JFrame constructor Copyright © 2008-2013 Curt Hill

17. The Rest of main We set the size with: w.setSize(300,200); We place it on the desktop with: w.setLocation(100,100); Show the window: w.setVisible(true); The code will then look like the next screen Copyright © 2008-2013 Curt Hill

18. The First Amount of Code Copyright © 2008-2013 Curt Hill

19. Now What? The program is just the shell of a Windows program Lets run it and see what happens Try out the buttons on title bar –Minimize –Maximize/Restore –Kill Copyright © 2008-2013 Curt Hill

20. First Run Copyright © 2008-2013 Curt Hill

21. Now What? This program did not have the things promised –No buttons –No text fields –No nothing Here is where we start adding the components We will initialize them in the init method that was createdLayout Manager Copyright © 2008-2013 Curt Hill

22. Layout Manager The default layout manager for JFrame is BorderLayout This has its uses but overall will not work well for this application Instead lets use Flow, which is the default for Applets We need two things –Import –Code Copyright © 2008-2013 Curt Hill

23. What do we need? Need a new import statement: import java.awt.*; –This should follow the other import at the front In the init method add the following code: FlowLayout flow = new FlowLayout(); setLayout(flow); Copyright © 2008-2013 Curt Hill

24. Adding Widgets The change of the layout manager must occur before any other widget or control is added To add a simple control there is a four step process: –Declare the control –Instantiate the control with the new keyword –Set any other values needed –Add it Copyright © 2008-2013 Curt Hill

25. Declaration The declaration right after the class header In our case that is this: public class Win1 extends JFrame { So add one label after that: JLabel lab1 = null; Copyright © 2008-2013 Curt Hill

26. Instantiate The instantiation will go into the init method: void init() { lab1 = new JLabel(“Enter age in years:”); There is nothing else for a label so add: add(lab1); Lets run it Copyright © 2008-2013 Curt Hill

27. One More Thing Each control or widget may need an import Java allows wildcards on imports Change the generated import from: import javax.swing.JFrame; Into import javax.swing.*; This also gives us JLabel, JButton etc Copyright © 2008-2013 Curt Hill

28. Another Run Copyright © 2008-2013 Curt Hill

29. Next The next thing to do is add the input box This is the Java JTextField Similar to the JLabel as far as adding JTextField text = null; … text = new JTextField(5); add(text); The 5 is the number of columns Copyright © 2008-2013 Curt Hill

30. Buttons The hard one is buttons They have the declaration, instantiation, adding of Labels and TextAreas They also need an event handler The event handler is triggered by the Action Listener Gets somewhat uglier at this point Copyright © 2008-2013 Curt Hill

31. Action Listeners The main program is a class It starts right after the imports with a public class declaration and proceeds to end of program –So far We now need to create an ActionListener This handles the notification that the button has been clicked Then calls a method in the Win1 class Copyright © 2008-2013 Curt Hill

32. Shape ActionListeners always have a characteristic form Usually about 10-12 lines A sample is given next Explanation follows Copyright © 2008-2013 Curt Hill

33. Sample Listener Copyright © 2008-2013 Curt Hill class LClass implements ActionListener{ MyFrame adapter; LClass(MyFrame a){ adapter = a; } // end of constructor public void actionPerformed(ActionEvent e){ // Call event handler adapter.eventHandler(); } // end of actionPerformed } // end of LClass

34. Class Name The class name in this example was LClass It may be any Java name Should not match any other name in the program We will use that when we add the action listener Copyright © 2008-2013 Curt Hill

35. Window Name The MyFrame class in the previous screen should be the name of the windows class that you created In our example this line was the main program: public class Win1 extends … Then we should see: Win1 adapter; LClass(Win1 a){ –In the second and third line Copyright © 2008-2013 Curt Hill

36. Event Handler The actionPerformed method called the eventHandler method of our main windows program This method name should match a public void method in the main window class Like the class name it does not matter what you make it, except that it matches the actual method name Copyright © 2008-2013 Curt Hill

37. More Details The event handlers need: import java.awt.event.*; This is how the system knows what an action performed item is supposed to do Next is the modified Lclass Copyright © 2008-2013 Curt Hill

38. Inserted ActionListener Copyright © 2008-2013 Curt Hill

39. The Button Now we can insert the button code into the init method The usual code and another call button1 = new JButton("Calculate"); button1.addActionListener( new LClass(this)); add(button1); Copyright © 2008-2013 Curt Hill

40. Button Picture Copyright © 2008-2013 Curt Hill

41. Event Handler The action listener class called a method in the windows class In our example the code was: adapter.eventHandler(); Now we have to make that method do something Copyright © 2008-2013 Curt Hill

42. The Skeleton Such a method will have the following outer part: void eventHandler(){ … } What do we now want to do? Many programs have this basic form: // Get data // Do computations // Display results Copyright © 2008-2013 Curt Hill

43. Getting Data The main problem is that a textfield always has text in it –The type is String If we are interested in numerics then we must convert to a number This is done with static methods of a wrapper class We could use Scanner but that is more console/file based Copyright © 2008-2013 Curt Hill

44. TextField to Numerics To convert an edit box value to a usable numeric value, we use the wrapper classes –Integer –Double Thus code like this: 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 Copyright © 2008-2013 Curt Hill

45. Back to a String To display a result in either a TextField or Label 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)); Copyright © 2008-2013 Curt Hill

46. 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 valueOf s = a; // Illegal s = String.valueOf(a); // OK Copyright © 2008-2013 Curt Hill

47. 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); Copyright © 2008-2013 Curt Hill

48. 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 Copyright © 2008-2013 Curt Hill

49. 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()); Copyright © 2008-2013 Curt Hill

50. 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 minute double sec = years*365.25*24*60*60; Copyright © 2008-2013 Curt Hill

51. Display Results System.out.println is mostly used for console programs In a GUI we put the result in a Label or TextField In this example the label is named answer We use the setText method: answer.setText(“”+sec); Copyright © 2008-2013 Curt Hill

52. Event Handler and Run Copyright © 2008-2013 Curt Hill

53. Are we done? This program is now 61 lines It still needs some work: –An exit button –An about button However, most of that can wait until we get this part under control Copyright © 2008-2013 Curt Hill

54. New Button Exit button is simple, add a new: –Button –Listening class –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 Copyright © 2008-2013 Curt Hill

55. With Exit Button Copyright © 2008-2013 Curt Hill

56. Shell programming Eighty or more lines is likely more than we want to type for each program What many programmers do is modify a previous program into their next one Lots of this program could be recycled How would that work? Copyright © 2008-2013 Curt Hill

57. The Windows Shell Attached to the web site is a shell program It is the do-nothing windows program It contains instructions on how to modify it inside comments The standard Windows shell comes with one jTextField, several jLabels and three jButtons Copyright © 2008-2013 Curt Hill

58. Process The process is fully described in the shell itself Create new project and class Copy the shell in over everything except the package statement Use Replace to change the WinShell name with the one you created above Then customize the program as needed Copyright © 2008-2013 Curt Hill

59. Customization The instructions to customize the program are coded with /*-- These can be searched for and modifications made If a new button is needed then the instructions to do that are coded with a /*++ Copyright © 2008-2013 Curt Hill

60. WinShell Lets walk through the process a second time with WinShell This one will be quicker We will close all previous projects First create a new project and add a class Paste in WinShell Modify Run Copyright © 2008-2013 Curt Hill

61. Started Copyright © 2008-2013 Curt Hill

62. Delete Program Copyright © 2008-2013 Curt Hill

63. Paste in WinShell Copyright © 2008-2013 Curt Hill

64. Start Replace Copyright © 2008-2013 Curt Hill

65. Replace Dialog Copyright © 2008-2013 Curt Hill

66. Change About Copyright © 2008-2013 Curt Hill

67. Captions Copyright © 2008-2013 Curt Hill

68. Main method Copyright © 2008-2013 Curt Hill

69. Event Handler Copyright © 2008-2013 Curt Hill

70. Run Copyright © 2008-2013 Curt Hill

71. Lastly We will next do the demo The windows shell from the web page will be used There is quite a few things that need to be changed Not nearly as many as if typed in new Copyright © 2008-2013 Curt Hill