Swing (Java): Difference between revisions

Revision as of 18:11, 4 April 2023

Revision as of 21:17, 6 November 2023

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The <code>'''Hello'''</code> class <code>'''extends'''</code> the '''{{Javadoc|module=java.desktop|package=javax.swing|class=JFrame|text=JFrame|monotype=y}}''' class; the <code>JFrame</code> class implements a [[window (computing)|window]] with a [[title bar]] and a close [[Graphical control element|control]].

The <code>'''Hello()'''</code> [[constructor (object-oriented programming)|constructor]] initializes the frame by first calling the superclass constructor, passing the parameter <code>"helloHello World"</code>, which is used as the window's title. It then calls the '''{{Javadoc|module=java.desktop|package=javax.swing|class=JFrame|member=setDefaultCloseOperation(int)|text=setDefaultCloseOperation(int)|monotype=y}}''' method inherited from <code>JFrame</code> to set the default operation when the close control on the title bar is selected to '''{{Javadoc|module=java.desktop|package=javax.swing|class=WindowConstants|member=EXIT_ON_CLOSE|text=WindowConstants.EXIT_ON_CLOSE|monotype=y}}'''{{snd}} this causes the <code>JFrame</code> to be disposed of when the frame is closed (as opposed to merely hidden), which allows the Java virtual machine to exit and the program to terminate. Next, a '''{{Javadoc|module=java.desktop|package=javax.swing|class=JLabel|text=JLabel|monotype=y}}''' is created for the string '''"Hello, world!"''' and the '''{{Javadoc|module=java.desktop|package=java.awt|class=Container|member=add(java.awt.Component)|text=add(Component)|monotype=y}}''' method inherited from the {{Javadoc|module=java.desktop|package=java.awt|class=Container|text=Container|monotype=y}} superclass is called to add the label to the frame. The '''{{Javadoc|module=java.desktop|package=java.awt|class=Window|text=pack()|member=pack()|monotype=y}}''' method inherited from the {{Javadoc|module=java.desktop|package=java.awt|class=Window|text=Window|monotype=y}} superclass is called to size the window and lay out its contents.

The <code>'''main()'''</code> method is called by the Java virtual machine when the program starts. It [[Object (computer science)|instantiates]] a new '''<code>Hello</code>''' frame and causes it to be displayed by calling the '''{{Javadoc|module=java.desktop|package=java.awt|class=Component|member=setVisible(boolean)|text=setVisible(boolean)|monotype=y}}''' method inherited from the {{Javadoc|module=java.desktop|package=java.awt|class=Component|text=Component|monotype=y}} superclass with the boolean parameter <code>'''true'''</code>. The code uses the '''{{Javadoc|module=java.desktop|package=javax.swing|class=SwingUtilities|member=invokeLater(java.lang.Runnable)|text=invokeLater(Runnable)|monotype=y}}''' method to invoke the constructor from the AWT [[event dispatching thread]] in order to ensure the code is executed in a [[thread-safe]] manner. Once the frame is displayed, exiting the <code>main</code> method does not cause the program to terminate because the event dispatching thread remains active until all of the Swing top-level windows have been disposed.