Eliminating FOR Loops in Java Code

Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License

Campagna Anti-IF:
Java e i linguaggi dinamici,
incrementare le potenzialità
espressive di Java
[“Eliminare” i FOR]

Francesco Cirillo – francesco.cirillo@metodiagili.it- MetodiAgili.it
Javaday Roma - 01/12/2007

Campagna Anti-IF


Obiettivo

Più potere a Java “senza” i FOR
− Paper su come “eliminare” i FOR
Esperienza di design evolutivo
− Attraverso il refactoring
− Usando i principi di design
Far vincere qualche maglietta :)


Sviluppo Java Web: lento!

News Aggregator@xpug.it
http://it.groups.yahoo.com/group/extremeprogramming-it/message/4485:
http://it.groups.yahoo.com/group/extremeprogramming-it/message/4485:
……
> E poi detta tutta java a sviluppo web non è così tanto veloce in una
> E poi detta tutta java a sviluppo web non è così tanto veloce in una
> giornata non si riesce.
> giornata non si riesce.
su questo no :-) Direi che una prima iterazione con tutte le funzionalita'
su questo no :-) Direi che una prima iterazione con tutte le funzionalita'
di base in una giornata con 2 coppie si riesce a fare.
di base in una giornata con 2 coppie si riesce a fare.
> Con Rails in mezza o 1/4 :) ma non entriamo in guerre di religione.
> Con Rails in mezza o 1/4 :) ma non entriamo in guerre di religione.
Se non si riesce probabilmente le storie non sono state spezzate in modo
Se non si riesce probabilmente le storie non sono state spezzate in modo
iterativo-incrementale/verticale ;-)
iterativo-incrementale/verticale ;-)
……


Il problema
////class Department
class Department Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License
public void printSlips() {{
public void printSlips()
Resource resource = null;
Resource resource = null; (resources select: inForce) do: printSlip.
(resources select: inForce) do: printSlip.
for(int i=0; i i< _resources.size();i++) {{
for(int i=0; < _resources.size();i++)
resource = (Resource)_resources.get(i);
if(resource.lastContract().deadline().after(new Date())) {{
if(resource.lastContract().deadline().after(new Date()))
System.out.println(resource.name());
System.out.println(resource.salary());
}}
}}
}} for (Resource eachResource: _resources) {{
for (Resource eachResource: _resources)
if(eachResource.lastContract().deadline().after(new Date()) )){{
if(eachResource.lastContract().deadline().after(new Date())
System.out.println(eachResource.name());
“Our job is to solve problems, not spoonfeed compilers (…)
System.out.println(eachResource.salary());
We need clarity soSystem.out.println(eachResource.salary());
We need clarity sowe can communicate using our code. We
we can communicate using our code. We
}}
value conciseness and the ability to express aarequirement in
value conciseness and the ability to express requirement in
}}
code accurately and efficiently”.
--Dave Thomas
--Dave Thomas

Parliamo di design
}}
}}
}}


Parliamo di design
Resource resource = null; Ciclo?+Navigazione?
Ciclo?+Navigazione?
Ciclo?+Navigazione?
Selezione?
Selezione? if(resource.lastContract().deadline().after(new Date())) {{
System.out.println(resource.name()); Contenuti?
Media?
Media?
}}
}}
Layout?
Layout?
}}

public void printSlipForEach() { {
public void printSlipForEach() Ciclo?
Ciclo?
for (Resource eachResource: _resources) { {
for (Resource eachResource: _resources)
if(eachResource.lastContract().deadline().after(new Date()) ) ){ {
}}
}}
}}

Abbassare la complessità

Il Refactoring:
− Aumentare la capacità del codice di rivelare le
Lightweight
intenzioni di design, a qualsiasi membro del team,
Lightweight
alla prima occhiata
− Migliorare la struttura interna del sistema,
consentendo alle necessarie astrazioni di emergere
We need clarity so we can communicate using our code. We
We need clarity so we can communicate using our code. We
value conciseness and the ability to express aarequirement in
value conciseness and the ability to express requirement in
--Dave Thomas
--Dave Thomas

Step 1: Separare le logiche
////class Department Department
////class
class Department Department
class Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License
public void printSlips() {{ printSlips()
public void
Resource eachResource = null;
Resource eachResource = null;
List inforces = new ArrayList();
List inforces = new ArrayList();
resource for(int i=0; i i< _resources.size();i++) {{
resource= (Resource)_resources.get(i);
= (Resource)_resources.get(i);
Selezione? eachResource = (Resource)_resources.get(i);
eachResource = (Resource)_resources.get(i);
Selezione? if(resource.lastContract().deadline().after(new Date()))
if(eachResource.lastContract().deadline().after(new Date()) )){{
System.out.println(resource.name()); Stampa busta?
System.out.println(resource.name()); Stampa busta?
inforces.add(eachResource);
}} }}
}} }}
}} Resource eachInForce = null;
Resource eachInForce = null;
for(int i=0; i i< inforces.size();i++) {{
for(int i=0; < inforces.size();i++)
eachInForce = (Resource)inforces.get(i);
System.out.println(eachInForce.name());
System.out.println(eachInForce.salary());

}}
Francesco Cirillo – }}
francesco.cirillo@metodiagili.it- MetodiAgili.it

Step 2: Semplificare il FOR
……
……
for(int i=0; < inforces.size();i++) Ciclo ++navigazione
Ciclo navigazione
System.out.println(eachInForce.name()); Logica i-esima i-
System.out.println(eachInForce.salary()); Logica i-esima
}}
}}
new Block() {{
new Block()
public void evaluate(Resource each) {{
public void evaluate(Resource each)
System.out.println(each.name());
System.out.println(each.salary());
}}.evaluate(eachInForce);


……
……
for(int i=0; < inforces.size();i++) Ciclo ++navigazione
Ciclo navigazione
new Block() {{
new Block()
public void evaluate(Resource each) {{
public void evaluate(Resource each)
Logica i-i-esima
Logicai-esima
}}
}}


……
……
Ciclo ++navigazione
for(int i=0; < inforces.size();i++) Ciclo navigazione

new PrintSlip().evaluate(eachInForce); Logica i-i-esima
new PrintSlip().evaluate(eachInForce); Logicai-esima
}}
}}

public class PrintSlip implements Block {{
public class PrintSlip implements Block
public void evaluate(Resource aResource) {{
public void evaluate(Resource aResource)
System.out.println(aResource.name());
System.out.println(aResource.salary());
}}
}}

Step 3: Eliminare il FOR
……
……
Ciclo ++navigazione
for(int i=0; < inforces.size();i++) Ciclo navigazione

new PrintSlip().evaluate(eachInForce); Logica i-i-esima
new PrintSlip().evaluate(eachInForce); Logicai-esima
}}
}}

}}
}}

……
……
Iterator iterator = inforces.iterator();
Iterator iterator = inforces.iterator(); Ciclo
Ciclo
while(iterator.hasNext()) {{
while(iterator.hasNext())
new PrintSlip().evaluate(iterator.next()); Logica i-i-esima
new PrintSlip().evaluate(iterator.next()); Logicai-esima
}}
}}

}}
}}

public void printSlips(…) {{
public void printSlips(…)
……
……
Iterator iterator = inforces.iterator();
Iterator iterator = inforces.iterator(); Ciclo
Ciclo
aBlock.evaluate(iterator.next());
aBlock.evaluate(iterator.next()); Logica i-i-esima
Logicai-esima
}}
}}

}}
}}

public class ResourceOrderedCollection {{
public class ResourceOrderedCollection
private Collection _items;
private Collection _items; Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License

public ResourceOrderedCollection(Collection items) {{
public ResourceOrderedCollection(Collection items) Navigazione
Navigazione
_items ==items;
_items items;
}}

public void forEachDo(Block aBlock) {{
public void forEachDo(Block aBlock)
Iterator iterator ==_items.iterator();
Iterator iterator _items.iterator(); Ciclo
Ciclo
aBlock.evaluate((Resource)iterator.next());
}}
}} public void printSlips() {{
}} Resource eachResource ==null;
Resource eachResource null;
List inforces ==new ArrayList();
List inforces new ArrayList();
for(int i=0; i i<<_resources.size();i++) {{
for(int i=0; _resources.size();i++)
eachResource ==(Resource)_resources.get(i);
eachResource (Resource)_resources.get(i);
if(eachResource.lastContract().deadline().after(new Date()) ) ){{
}}
}}
new ResourceOrderedCollection(inforces).forEachDo(new PrintSlip());
}}

Step 4: E la selezione
public void printSlips() Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License
Resource eachResource ==null;
List inforces new ArrayList(); Ciclo ++navigazione
Ciclo navigazione
if(eachResource.lastContract().deadline().after(new Date()) ) ){{ Selezione
Selezione
Logica i-i-esima
Logicai-esima if(eachResource.lastContract().deadline().after(new Date())
inforces.add(eachResource); Addizione
Addizione
}}
}} public void printSlips() {{
}} List inforces ==new ArrayList();
List inforces new ArrayList();
if(new PredicateBlock() {{
if(new PredicateBlock()
public boolean is(Resource each) {{
public boolean is(Resource each)
return each.lastContract().deadline().after(new Date());
}}.is(eachResource) {{
}}.is(eachResource)
}}
}}
}}

List inforces new ArrayList(); Ciclo ++navigazione
Ciclo navigazione
if(new InForcePredicate().is(eachResource)) {{
if(new InForcePredicate().is(eachResource))
inforces.add(eachResource); Addizione
Addizione
}}
}}
}}

public class InForcePredicate implements PredicateBlock {{
public class InForcePredicate implements PredicateBlock
public boolean is(Resource each) Selezione
Selezione
}}
}}


Collection inforces ==new ResourceOrderedCollection(_resources).select(new InForce());
Collection inforces new ResourceOrderedCollection(_resources).select(new InForce());
}}

public Collection select(PredicateBlock aBlock) {{
public Collection select(PredicateBlock aBlock)
Collection result ==new ArrayList();
Collection result new ArrayList();
Iterator iterator _items.iterator(); Navigazione
Navigazione
while(iterator.hasNext()) {{ Ciclo
Ciclo
Resource resource ==(Resource)iterator.next();
Resource resource (Resource)iterator.next();
ifif(aBlock.is(resource)) result.add(resource);
(aBlock.is(resource)) result.add(resource); Addizione
Addizione
}}
return result;
return result;
}}

public class InForcePredicate implements PredicateBlock {{
public boolean is(Resource each) Selezione
Selezione
}}
}}

Step 5: Per leggere meglio
Collection inforces ==new ResourceOrderedCollection(_resources).select(new InForce());
Collection inforces new ResourceOrderedCollection(_resources).select(new InForce());
}} public void printSlips() {
public void printSlips() {
(new ResourceOrderedCollection(_resources).select(new InForce()).forEachDo(new PrintSlip());
(new ResourceOrderedCollection(_resources).select(new InForce()).forEachDo(new PrintSlip());
}} public ResourceOrderedCollection select(PredicateBlock aBlock) {
public ResourceOrderedCollection select(PredicateBlock aBlock) {
ResourceOrderedCollection result ==new ResourceOrderedCollection();
ResourceOrderedCollection result new ResourceOrderedCollection();
Iterator iterator _items.iterator();
(aBlock.is(resource)) result.add(resource);
}}
return result;
return result;
}}
Predicate isInForce ==new InForce();
Predicate isInForce new InForce();
Block printSlip ==new PrintSlip();
Block printSlip new PrintSlip();
ResourceOrderedCollection resources ==new ResourceOrderedCollection(_resources);
ResourceOrderedCollection resources new ResourceOrderedCollection(_resources);
resources.select(isInForce).forEachDo(printSlip);
}}

Step 5: Per leggere meglio
Predicate isInForce ==new InForce();
Predicate isInForce new InForce();
Block printSlip ==new PrintSlip();
Block printSlip new PrintSlip();
ResourceOrderedCollection resources ==new ResourceOrderedCollection(_resources);
ResourceOrderedCollection resources new ResourceOrderedCollection(_resources);
}}

printSlipsUsing(new InForce(),new PrintSlip());
printSlipsUsing(new InForce(),new PrintSlip());
}}
private void printSlipsUsing(Predicate aCriterium, Block anAction) {{
private void printSlipsUsing(Predicate aCriterium, Block anAction)
new ResourceOrderedCollection(_resources).select(aCriterium).forEachDo(anAction);
new ResourceOrderedCollection(_resources).select(aCriterium).forEachDo(anAction);
}}

public void printSlipsUsing(Predicate aCriterium, Block anAction) {{
public void printSlipsUsing(Predicate aCriterium, Block anAction)
_resources.select(aCriterium).forEachDo(anAction);
_resources.select(aCriterium).forEachDo(anAction);
}}
private ResourceOrderedCollection _resources;
private ResourceOrderedCollection _resources;


Step 6: Generalizzare
new ResourceOrderedCollection(resources).select(isInForce).forEachDo(printSlip);
public class ResourceOrderedCollection { {
……
public void forEachDo(Block aBlock) { {
public void forEachDo(Block aBlock)
while(iterator.hasNext()) { { public class PrintSlip implements Block { {
aBlock.evaluate((Resource)iterator.next()); public void evaluate(Resource aResource) { {
}} System.out.println(aResource.name());
}} System.out.println(aResource.salary());
public ResourceOrderedCollection select(Predicate aBlock) { { }}
public ResourceOrderedCollection select(Predicate aBlock)
ResourceOrderedCollection result ==
ResourceOrderedCollection result }}
new ResourceOrderedCollection();
while(iterator.hasNext()) { {
}}
return result;
return result;
}} public class InForcePredicate implements PredicateBlock { {
}} public boolean is(Resource each) { {
}}
}}

Step 6: Generalizzare
public class ResourceOrderedCollection { {
… public class OrderedCollection { {
public class OrderedCollection
… ……
public void forEachDo(Block aBlock) {class InForcePredicate implements Predicate {
public void forEachDo(Block aBlock) {class InForcePredicate implements Predicate {
public
public public void forEachDo(Block aBlock) { {
Iterator iterator ==_items.iterator(); boolean is(Object anObject) { forEachDo(Block aBlock)
public void
Iterator iterator _items.iterator(); boolean is(Object anObject) { iterator = _items.iterator();
public
while(iterator.hasNext()) { { public Iterator iterator = _items.iterator();
Iterator
while(iterator.hasNext()) return ((Resource)anObject).lastContract().deadline().after(new Date());
return ((Resource)anObject).lastContract().deadline().after(new Date());
aBlock.evaluate((Resource)iterator.next()); while(iterator.hasNext())
}} aBlock.evaluate(iterator.next());
}} aBlock.evaluate(iterator.next());
}} }}
}}
public class PrintSlip implements Block {
public ResourceOrderedCollection Block {
public class PrintSlip implements }}
public ResourceOrderedCollectionselect(Predicate aBlock) { { public OrderedCollection select(Predicate aBlock) {
select(Predicate aBlock)
public void evaluate(Resource aResource) { {
ResourceOrderedCollection result == public OrderedCollection select(Predicate aBlock) {
ResourceOrderedCollection result
System.out.println(aResource.name()); OrderedCollection result ==
new ResourceOrderedCollection(); OrderedCollection result
System.out.println(aResource.salary()); new OrderedCollection();
Iterator System.out.println(aResource.salary());
Iteratoriterator ==_items.iterator();
iterator _items.iterator(); new OrderedCollection();
}}
while(iterator.hasNext()) { { Iterator iterator ==_items.iterator();
}} while(iterator.hasNext()) while(iterator.hasNext()) { {
Resource resource ==(Resource)iterator.next(); while(iterator.hasNext())
Resource resource (Resource)iterator.next(); PrintSlip implements Block { = iterator.next();
public class PrintSlip implements object { = iterator.next();
public class Object Block
Object object
}} public void evaluate(Object anObject) { { result.add(object);
ifif(aBlock.is(object)) result.add(object);
(aBlock.is(object))
public void evaluate(Object anObject)
return result; }}
System.out.println(((Resource)anObject).name());
return result; System.out.println(((Resource)anObject).name());
return result;
}} System.out.println(((Resource)anObject).salary());}
return result;
System.out.println(((Resource)anObject).salary());}
}} }} }}
public class InForcePredicate implements PredicateBlock { { }
public boolean is(Resource each) { { }
} } Cirillo – francesco.cirillo@metodiagili.it- MetodiAgili.it
Francesco
}}

Dove siamo
Resource resource = null; Navigazione?
Navigazione?
Selezione?
Selezione? if(resource.lastContract().deadline().after(new Date())) {{
Media?
Media?
}}
}}
Layout?
Layout?
}}

_resources.select(onlyWomen).forEachDo(printReport);
_resources.select(isInForce).forEachDo(printSlip);
_resources.select(onlyWomen).forEachDo(printReport);

Contenuti+
Contenuti+
Navigazione
Navigazione Selezione
Selezione Media+
Media+
Layout
Layout


class Department
public void printSlips() { {
Review & ToDoList
Resource resource ==null;
Resource resource null;
for(int i=0; i i<<_resources.size();i++) { {
Navigazione?
Navigazione?

resource ==(Resource)_resources.get(i);
resource (Resource)_resources.get(i);
Selezione?
Selezione? if(resource.lastContract().deadline().after(new Date())) { {
System.out.println(resource.name()); Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License
Media? System.out.println(resource.salary()); Contenuti?
Contenuti?
Media? System.out.println(resource.salary());
}}
}}
}}
Layout?
Layout?

10/01-10/11/2007:Contract

Andrea:Employee

“Andrea”:String
:Department
Federica:Manager

1/9/2007-10/10/2008:Contract

“Federica”:String
System.out:PrintStream


Review & ToDoList
public OrderedCollection select(Predicate aBlock) { {
public OrderedCollection select(Predicate aBlock)
OrderedCollection result ==new publicCreative Commons Attribution-NonCommercial-ShareAlike 2.5 License
OrderedCollection result new
OrderedCollection(); publicboolean is(Object each) { {
boolean is(Object each)
OrderedCollection();
_resources.select(isInForce).forEachDo(printSlip); return ((Resource)each).lastContract().deadline().after(new Date());
return ((Resource)each).lastContract().deadline().after(new Date());
Iterator iterator _items.iterator(); }}
Object object ==iterator.next();
Object object iterator.next();
ifif(aBlock.is(object)) result.add(object);
(aBlock.is(object)) result.add(object);
}}
return result; 10/01-10/11/2007:Contract
return result;
}}

resources:OrderedCollection Andrea:Employee

:InForce “Andrea”:String
:Department
inForce:OrderedCollection Federica:Manager

1/9/2007-10/10/2008:Contract
:PrintSlip




Review & ToDoList
public OrderedCollection select(Predicate aBlock) { {
public class PrintSlip implements Block { { aBlock)
public OrderedCollection select(Predicate
OrderedCollection result ==new
public void forEachDo(Block aBlock) { {
public void forEachDo(Block aBlock) public void evaluate(Objectnew
OrderedCollection result anObject) {
OrderedCollection();
public void evaluate(Object anObject) {
Iterator iterator _items.iterator(); OrderedCollection();
IteratorSystem.out.println(((Resource)anObject).name());
Iteratoriterator ==_items.iterator();
System.out.println(((Resource)anObject).name());
iterator _items.iterator();
while(iterator.hasNext()) System.out.println(((Resource)anObject).salary());
System.out.println(((Resource)anObject).salary());
aBlock.evaluate(iterator.next());
aBlock.evaluate(iterator.next()); } } Object object ==iterator.next();
Object object iterator.next();
}} }} ifif(aBlock.is(object)) result.add(object);
}} (aBlock.is(object)) result.add(object);
}}
return result;
return result;
10/01-10/11/2007:Contract
}}

resources:OrderedCollection Andrea:Employee

:InForce “Andrea”:String
:Department
inForce:OrderedCollection Federica:Manager

1/9/2007-10/10/2008:Contract
:PrintSlip




Riferimenti blocchi e
chiusure

Blocchi in Java
− http://www.c2.com/cgi/wiki?BlocksInJava
Blocchi e chiusure in Ruby
− http://www.artima.com/intv/closuresP.html
Chiusure nel linguaggio Java
− http://www.javac.info/closures-v03.html
Esempi di librerie
− http://jaggregate.sourceforge.net


Segui la Campagna Anti-IF


Domande

Risorse:
http://www.xplabs.it/risorse.html
http://www.metodiagili.it/campagna-anti-if.html

Tecnica del Pomodoro:
http://www.tecnicadelpomodoro.it

EasyTracking:
http://www.myagileprojects.com

Gruppo XPLabs’ Friends- Italia:
http://it.groups.yahoo.com/group/xplabs-friends/

Extreme Programming User Group – Italia:
http://www.xpug.it/

Eliminating FOR Loops in Java Code

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