Swing and JButton

Importance of Swing

 Swing was created to address the limitations present in the AWT. It does this through two key features: lightweight components and a pluggable look and feel. Together they provide an elegant, yet easy-to-use solution to the problems of the AWT. More than anything else, it is these two features that define the essence of Swing.

Swing Components are LightWeight

With very few exceptions, Swing components are lightweight. This means that they are written entirely in Java and do not map directly to platform-specific peers. Thus, lightweight components are more efficient and more flexible. Furthermore, because lightweight components do not translate into native peers, the look and feel of each component is determined by Swing, not by the underlying operating system. As a result, each component will work in a consistent manner across all platforms.

Swing Supports a Pluggable Look and Feel

Swing supports a pluggable look and feel (PLAF). Because each Swing component is rendered by Java code rather than by native peers, the look and feel of a component is under the control of Swing. This fact means that it is possible to separate the look and feel of a component from the logic of the component, and this is what Swing does. Separating out the look and feel provides a significant advantage: it becomes possible to change the way that a component is rendered without affecting any of its other aspects. In other words, it is possible to “plug in” a new look and feel for any given component without creating any side effects in the code that uses that component. Moreover, it becomes possible to define entire sets of look-and-feels that represent different GUI styles. To use a specific style, its look and feel is simply “plugged in.” Once this is done, all components are automatically rendered using that style. 

Pluggable look-and-feels offer several important advantages. It is possible to define a look and feel that is consistent across all platforms. Conversely, it is possible to create a look and feel that acts like a specific platform. It is also possible to design a custom look and feel. Finally, the look and feel can be changed dynamically at run time. 

JButton

JButton jtnAlpha = new JButton("Alpha");

JButton jtnBeta = new JButton("Beta");

The first button will contain the text "Alpha" and the second will contain the text "Beta". Swing push buttons are instances of JButton. JButton supplies several constructors. The one used here is 

JButton(String msg) 

The msg parameter specifies the string that will be displayed inside the button. When a push button is pressed, it generates an ActionEvent. Thus, JButton provides the addActionListener( ) method, which is used to add an action listener. (JButton also provides removeActionListener( ) to remove a listener, but this method is not used by the program.)