Chapter 8.5, Problem 34STQ

Program Plan Intro

Survey of standard Java library:

Consider the package “java.lang” from the standard Java library:

• The “java.lang” package has three classes.
• The three classes that implement equals method correctly are as follows:
  • Wrapper classes
  • Class “String”
  • StackTraceElement
• The above three classes fulfill the axioms in the Java API specification.
• Some of the classes use “instanceof”, but there is no difficulty with subclasses because they are final classes.

Consider the package “java.awt” from the standard Java library:

• The “java.awt” package has 80 classes.
• The four classes that implement equals correctly are as follows:
  • AlphaComposite
  • DisplayMode
  • JobAttributes
  • PageAttributes
• Using “instanceof”, the non-final classes implements the following:
  • BasicStroke
  • Color
  • Dimension
  • Inserts
  • MenuShortcut
  • Point
  • Rectangle
  • RenderingHints
• Instead of “getClass” using “instanceof” does not create a problem for the java engineers because these classes are not sub classed.
• However, it is a problem for the people who wanted to have a subclass “LabeledPoint” or “ColoredPoint” of “Point” because the people would not be capable to redefine the equals method.

Consider the package “javax.swing” from the standard Java library:

• It is used to create window-based applications.
• On the top of AWT (Abstract Windowing Toolkit), the “javax.swing” was build.
• It provides classes for java swing API, such as “JTextField”, “JCheckbox”, “JTextField”, “JMenu”, “JButton”, “JTextArea”, “JColorChooser” etc.
• It provides lightweight components, and platform-independent.