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Decorator

Decorator. Josh Voils and Ralph Rodkey. GoF Definition of Intent. Attach additional responsibilities to an object dynamically Provide an alternative to subclassing for extending functionality. aBorderDecorator. aScrollDecorator. component. component. GoF Example.

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Decorator

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  1. Decorator Josh Voils and Ralph Rodkey

  2. GoF Definition of Intent • Attach additional responsibilities to an object dynamically • Provide an alternative to subclassing for extending functionality

  3. aBorderDecorator aScrollDecorator component component GoF Example • We want to add a border and a scroll bar to a TextView object • Let’s use a decorator! aTextView Instance diagram for our example

  4. VisualComponent Draw() component TextView Decorator component->Draw() Decorator::Draw() DrawBorder() Draw() Draw() ScrollDecorator BorderDecorator Draw() ScrollTo() scrollPosition Draw() DrawBorder() borderWidth The UML

  5. Challenge A • Why use a Decorator instead of subclassing?

  6. Streams • Java Streams are an example of a decorator • Challenge B: • Draw an analogy between the OutputStream hierarchy and the TextView hierarchy

  7. Oozinoz Writer • A writer is a stream that reads characters • Java Provides the filterWriter class to facilitate the creation of new filters • Here Metsker uses a FilterWriter to create an OozinozFilter

  8. OozinozFilter Code package com.oozinoz.io; import java.io.*; public abstract class OozinozFilter extends FilterWriter { protected OozinozFilter(Writer out) { super(out); } public void write(char cbuf[], int off, int len) throws IOException { for (int i = 0; i < len; i++) { write(cbuf[i]); } } public abstract void write(int c) throws IOException; public void write(String s, int off, int len) throws IOException { write(s.toCharArray(), off, len); } }

  9. O.W. (cont) • From the abstract OozinozFilter he creates some custom filters package com.oozinoz.io; import java.io.*; public class UpperCaseFilter extends OozinozFilter { public UpperCaseFilter(Writer out) { super(out); } public void write(int c) throws IOException { out.write(Character.toUpperCase((char) c)); } }

  10. Application of Filters package com.oozinoz.applications; import java.io.*; import com.oozinoz.io.*; public class ShowFilters { public static void main(String args[]) throws IOException { BufferedReader in = new BufferedReader(new FileReader(args[0])); Writer out = new FileWriter(args[1]); out = new WrapFilter(new BufferedWriter(out), 40); out = new TitleCaseFilter(out); while (true) { String s = in.readLine(); if (s == null) { break; } out.write(s + "\n"); } out.close(); in.close(); } } This program line-wraps text in an input file and puts it in title case

  11. Challenge 27.1 If you want to direct output to System.out instead of to a file, you can create a Writer object that directs its output to System.out: Writer out = new PrintWriter(System.out); Write a snippet of code to define a Writer object that wraps text at 15 characters, centers the text, sets the text to random casing, and directs the output to System.out.

  12. Challenge 27.1 Answer One answer is: Writer out = new PrintWriter(System.out); out = new WrapFilter(new BufferedWriter(out), 15); ((WrapFilter) out).setCenter(true); out = new RandomCaseFilter(out); Alternatively: WrapFilter out = new WrapFilter( new BufferedWriter( new RandomCaseFilter( new PrintWriter(System.out))), 15); out.setCenter(true);

  13. Challenge 27.5 (sorta) package com.oozinoz.applications; import javax.swing.*; import javax.swing.border.*; import java.awt.*; import com.oozinoz.ui.*; public class ShowBorders { protected static JButton createButton(String label) { JButton b = new JButton(label); b.setFont(SwingFacade.getStandardFont()); b.setFocusPainted(false); return b; } public static void main(String[] args) { JButton ignite = createButton("Ignite"); JButton launch = createButton("Launch"); launch.setBorder( new CompoundBorder( new LineBorder(Color.black, 4), new CompoundBorder( new BevelBorder(BevelBorder.RAISED), new EmptyBorder(10, 10, 10, 10)))); JPanel p = new JPanel(); p.add(ignite); p.add(launch); SwingFacade.launch(p, " Borders"); } } • Why are swing borders not decorators?

  14. Questions? Comments?

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