Clojure And Swing

Clojureand Swing – a new productivity sweet spot?Simon White

Skills MatterThe UK Open Source Training CompanyTraining on: Agile Development, Test Driven Development, Java, Eclipse, Spring, Hibernate, Ajax, Ruby on Rails, Struts Ti, Wicket, JavaServer Faces, Tapestry, Beehive, AOP, RIFE and more!Training straight from the SourceExperts write and teach our courses: Adrian Colyer, Chad Fowler, Howard M. Lewis Ship Craig Larman, Dave Crane, Kevlin Henney, Rob Harrop, Kito Mann, Rod Johnson and many morePartners with leading edge companiesBEA, IBM, Interface21, Sun, Tangosol, wso2© Catalysoft Ltd, 2010

Speaker QualificationsSimon White, IndependentJava developerGames published 1985PhD Artificial IntelligenceWritten Scientific Software for:Remote SensingDrug DiscoveryMedical & Genetics ResearchSwing Developer since 2000Author of JIDE ChartsSkillsMatter Author & Trainer© Catalysoft Ltd, 2010

What is Clojure?A functional language that runs on the JVMA new dialect of LISPNot ClosureNot ClozureMYTH: LISP is slowMYTH: Therefore Clojure is slow

Functional LanguagesWhat is a function?a mathematical relation such that each element of a given set (the domain of the function) is associated with an element of another set (the range of the function)) [Wordnet]Focus on the input/output relatione.g. length of a string maps a string to an integerImmutability Good; Side-effects Bad

LISP Syntax(functor param1 param2 ... paramn)for example, (+ 1 2)Brackets denote evaluationA single quote protects from evaluationso '(x y z) does not use x as a functionWith nested expressions, evaluate inner expression first: (+ (+ 2 3) (* 2 3)) is 11Special forms like let, cond deviate from the syntax and must be learned

Hello Factorialn! = n × (n-1) × (n-2) × ... × 1Also 0! = 1(defnfac “Computes the factorial of n” [n] (if (= n 0) 1 (* n (fac (- n 1)))))

REPLRead-Evaluate-Print-Loopuser=> (defn add-one [n] (+ 1 n))#'user/add-oneuser=> (add-one 6)7user=>

Why mix Java and LISP?To get the best of both:Speedy development of custom code in LISPSpeedy development through library reuse in JavaSpeedy development of applications with concurrent processing

LISP Promotes AgilityLISP was agile long before agility was respected Easy to mix and match function applicationAccommodate changing requirementsMany small functions => very reusable codeREPL Encourages ad-hoc testingFunctional style makes it easy to write unit tests

Clojureas a LISP dialectSimplified syntax compared to Common LISPcond, letNot object-orientedBut you can define structures and multi-methodsNo multiple value returnsArguably syntactic sugar anywayLazy evaluation of sequencesDestructuringStructural pattern matching on function parametersConcurrency

Data Structures 1: Lists(list 'a 'b 'c) -> (a b c)(first '(a b c)) -> a(rest '(a b c)) -> (b c)(nth '(a b c) 1) -> b(cons 'a '(b c)) -> (a b c)(concat '(a b) '(c d)) -> (a b c d)

Data Structures 2: Vectors(vector 'a 'b 'c) -> [a b c](first '[a b c]) -> a(rest '[a b c]) -> (b c)(nth '[a b c] 1) -> b(cons 'a '[b c]) -> (a b c)(conj '[a b] 'c) -> [a b c](concat '[a b] '[c d]) -> (a b c d)

Data Structures 3: MapsKey-Value Pairs(get '{a 1, b 2} 'b) -> 2(assoc '{a 1, b 2} 'c 3) -> {c 3, a 1, b 2}(dissoc '{a 1, b 2} 'b) -> {a 1}(defstruct book :title :author)(struct-map book :title "Jungle Book" :author "Rudyard Kipling") (bean obj)

Everything is a SequenceLists, Vectors and Maps are all sequencesfirst, rest & cons always return a sequence(range 5) -> (0 1 2 3 4)(take 2 (range 5)) -> (0 1)(take 3 (repeat 'x)) -> (x xx)

Predicates (Boolean-Valued Tests)(= a 10)(identical? a b)(even? a)(odd? a)(integer? a)

Decisions(if (= a 1) 5 0)(cond (= a 1) 5 (= a 2) 10 true 0)(when (= a 1) 5)a == 1 ? 5 : 0Java

"Iteration"(for [a '(1 2 3)] (+ a 1)) -> (2 3 4)(doseq [a (range 5)] a) -> nil(doseq [a (range 3)] (println a)) ->012nil

Anonymous Functionsuser=> (fn [a b] (+ a b 1))#<user$eval__101$fn__103 ...@a613f8>user=> ((fn [a b] (+ a b 1)) 3 4)8user=> #(+ %1 %2)#<user$eval__121$fn__123 ...@56f631>

Higher Order Functions(inc 1)->2(map inc '(1 2 3))->(2 3 4)(map + '(1 2 3) '(10 11 12))->(11 13 15)(max 1 2 3)->3(apply max '(1 2 3))->3(filter even? (range 10))->(0 2 4 6 8)

Partial FunctionsPartial returns a functionuser=> (def add-two (partial + 2))#'user/add-twouser=> (add-two 5)7

A GUI in a functional language?Functional languages use functions as mathematical models of computation:f(x1, x2, ...) -> x’Great for factorials, but how does it work with user-interfaces?Forms?Keyboard & Mouse?Events?

Need to Think DifferentlyValues of functions ‘computed’ as the result of a user-interactionConsider y-or-n-pCL> (y-or-n-p "Do you really want to quit?")T

Modelling Change of Statef(x) -> x’Name: “George”DOB: “11-Jul-73”Address: “16 Goldman Square”Name: “George”DOB: “11-Jul-73”Address: “3 Elm Avenue”This is a new (immutable) value,not a modified one

Java Swing: Create a JFrameimport javax.swing.JFrame;public class MyClass {... public static void main(String[] args) {JFrame frame = new JFrame("My Frame");frame.setBounds(300, 300, 600, 400);frame.setVisible(true); }}

Clojure Swing: Create a JFrame(ns user (:import (javax.swingJFrame)))(defn make-frame [] (let [f (JFrame. "My Frame")] (.setBounds f 300 300 600 400) (.setVisible f true) f ) )f is the return value

Alternative: Use doto(defn make-frame [] (let [f (JFrame. "My Frame")] (doto f (.setBounds 300 300 600 400) (.setVisible true))))

Create a Panel & Button(ns user (:import java.awt.FlowLayout (javax.swingJButtonJPanel)))(defn make-panel [] (let [panel (JPanel. (FlowLayout.)) button (JButton. "Press Me")] (doto panel (.add button))))

Make a Button do Something(defn make-panel2 [] (let [panel (JPanel. (FlowLayout.)) button (JButton. "Press Me")] (.addActionListener button (proxy [ActionListener] [] (actionPerformed [e] (println e)))) (doto panel (.add button)) ) )#<ActionEventjava.awt.event.ActionEvent[ACTION_PERFORMED,cmd=Press Me...

Clojure Custom Component(defn make-component [msg] (proxy [javax.swing.JComponent] [] (paintComponent [g] (let [height (.getHeight this) width (.getWidth this)] (doto g ... )))))Detail on next slide

Custom Component (cont/d)(doto g (.setColorColor/gray) (.fillOval 20 20 (- width 20) (- height 20)) (.setColorColor/yellow) (.fillOval 0 0 (- width 20) (- height 20)) (.setFont (.deriveFont (.getFont g) (float 50))) (.setColorColor/black) (.drawStringmsg(int (/ (- width (.stringWidth (.getFontMetrics g) msg)) 2)) (int (/ height 2))))

Three ways in which Clojure can help SwingReducing boiler-plate codeEasy to write code that generates the required patternsDefinitions of actions and easier bindingEasier to separate configuration (name, icon, keyboard shortcut, ...) from code hookFlexibility and ReusabilityUsing functions as parameters for user customisation of behaviour

1. Reducing Boiler-Plate CodeGridBagConstraints c = new GridBagConstraints();c.weighty = 1.0;c.weightx = 1.0;c.insets = new Insets(5, 5, 5, 5);c.gridx = 0;c.gridy = 0;c.gridheight = 2;c.anchor = GridBagConstraints.CENTER;c.fill = GridBagConstraints.BOTH; add(leftListPane, c);c.gridx = 1;c.gridy = 0;c.gridheight = 1; ...GridBagConstraints are unwieldy

Use the same options a lot of the time

Difficult to understandUsing a grid-bag-layout macro(def panel (doto (JPanel. (GridBagLayout.)) (grid-bag-layout :fill :BOTH, :insets (Insets. 5 5 5 5) :gridx 0, :gridy 0 (JButton. "One") :gridy 1 (JButton. "Two") :gridx 1, :gridy 0, :gridheight 2 (JButton. "Three"))))See http://stuartsierra.com/2010/01/05/taming-the-gridbaglayout

2. Defining Swing ActionsSwing Actions are a nice idea, but have problems. Typically, you might have:Lots of inner classes with repeated boiler plate code, or:Separate classes that extend AbstractAction but are too tightly coupled to a main class so that they have the necessary context for the actionPerformed() method.

Clojure Actions: Defer binding for actionPerformed methodWith an Action in Clojure it’s possible to preset the ‘constant’ variables like Name, Icon, Accelerator ; but defer the binding for the handler.This means we can easily separate the creation of an action according to some template from its binding to a response function.

Create an Action when the handler function is known(defmacro copy-action [handler] `(make-action {:name "Copy" :command-key "copy" :icon (ImageIcon. (fetch-image "copy.png")) :handler ~handler :mnemonic (mnemonic \C) :accelerator (accelerator "ctrl C")}))

3. Flexibility and Reusability(def *tracing-actions* true) (defntrace-action [handler] (fn [#^ActionEvent e] (try (when *tracing-actions* (print "Doing" (.getActionCommand e))) (handler e) (finally (when *tracing-actions* (println "Done"))))))

Swing Worker & Busy Cursor(defmacro with-busy-cursor [component f] `(proxy [SwingWorker] [] (doInBackground [] (.setCursor ~component (Cursor/getPredefinedCursor Cursor/WAIT_CURSOR)) ~f) (done [] (.setCursor ~component (Cursor/getDefaultCursor)))))(with-busy-cursor chart (load-file data-file))

Clojure/Swing in the Real World

Creating a Chart Model(defn make-model "Create and return a ChartModel using the supplied rows and picking out the x and y columns" [model-name rows #^String x-col #^String y-col] (let [model (DefaultChartModel. model-name)] (doseq [row rows] (let [x (get row x-col) y (get row y-col)] (when (and (number? x) (number? y)) (.addPoint model (double x) (double y)))) ) model))

Clojure And Swing

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