Lecture 18

1. Create the component

2. Create a listener

3. Create an instance of the listener

4. Add (“register”) the listener to the component

5. Add the component to the JFrame

• You can skip steps 2 – 4 if your program doesn’t require an action

• How does this work?

  • Create a visual interface

  • A JFrame

  • A button

• Then implement a listener

  • this is the code which you wish to perform once the button Is pressed

• register the listener to the button

  • when the button is pressed

  • Java calls ActionPerformed

    • You do not call ActionPerformed

    • ActionPerformed is an automation in Java

• Registration tells Java to call it when the button is pressed

  • And then reads the listener

Labels

• can add a line of text using JLabel component

  1. create a component

  2. JLabel MyLabel = new JLabel(“My Label”);

  3. Skip

  4. Skip

  5. Skip

  6. Add the component to the JFrame

     • MyWindow.add(MyLabel);

Layouts

• We require a way to arrange multiple objects within a window

• Java technique which accomplishes that is the layout

  • BorderLayout

  • GridLayout

    • FlowLayout

• JFrame contains a method setLayout()

• MyWindow.setLayout(Layout l);

• Executing this sets the layout of the window to the layout object l.

• Andrew is not sure that setLayout take a Layout as its param, he will find out for next class

BorderLayout

• When Adding a component also specify a region in which It goes

  • MyWindow.add(MyButton, BorderLayout.North/East/South/West/Center)

GridLayout

GridLayout GL;

GL = new GridLayout (2, 3)

//2 = rows, 3 = columns

MyWindows.setLayout(GL);

JLabel Label 1 = new JLabel (“1”)

MyWindow.add (Label 1);

Flow Layout

flowLayout FL;

FL = newFlowLayout ();

MyWindow.setLayout (FL);

// add components

Good JFrame Practice

• Up to now, everything has been done in main

• This is bad practice because the window is an object

• It should be treated as such

• We are creating a modification of JFrame

• Use inheritance