Abstractie (Dutch)

wat?
waarom?
hoe?
valkuilen
conclusie

“Abstraction is the process of generalization by
reducing the information content of a concept in
order to retain only information which is relevant
for a particular purpose.”
-- Wikipedia (ed.)

bestanden
vensters

mappen

knoppen
multi-tasking

invoer velden

printChar('N'); char[] anBuffer = new char[255];
printChar('a'); int anLength = 0;
printChar('a'); do {
printChar('m'); inp = readChar();
printChar(':'); anBuffer[anLength] = inp;
printChar(' '); anLength++;
while (inp != 'n');
char[] vnBuffer = new char[255];
int vnLength = 0; printChar('H');
char inp; printChar('a');
do { printChar('l');
inp = readChar(); printChar('l');
vnBuffer[vnLength] = inp; printChar('o');
vnLength++; printChar(' ');
while (inp != 'n'); int i = 0;
while(i < vnLength) {
printChar('A'); printChar(vnBuffer[i]);
printChar('c'); i++;
printChar('h'); }
printChar('t'); printChar(' ');
printChar('e'); i = 0;
printChar('r'); while(i < anLength) {
printChar('n'); printChar(anBuffer[i]);
printChar('a'); i++;
printChar('a'); }
printChar('m');
printChar(':');

printChars(new char[] { 'N', 'a', 'a', 'm', ':', ' '}, 6);
char[] vnBuf = new char[255];
int vnLength = readChars(vnBuf);

printChars(new char[] { 'A', 'c', 'h', 't', 'e', 'r', 'n', 'a', 'a', 'm', ':', ' '},
12);
char[] anBuf = new char[255];
int anLength = readChars(vnBuf);

printChars(new char[] {'H', 'a', 'l', 'l', 'o', ' '}, 6);
printChars(vnBuf, vnLength);
printChars(anBuf, anLength);

String voornaam = readLine("Naam: ");
String achternaam = readLine("Achternaam: ");
print("Hallo " + voornaam + " " + achternaam);

FullName fn = FullName.read();
fn.printGreeting();

readNameAndPrintGreeting();

nieuwe eis: vraag ook naar leeftijd

readNameAndPrintGreeting();

nieuwe eis: vraag ook naar leeftijd ✖

fn.printGreeting();


fn.printGreeting();

nieuwe eis: vraag ook naar leeftijd ✖

print("Hallo " + voornaam + " " + achternaam);


int leeftijd = stringToInt(readLine("Leeftijd: "));
print("Hallo " + voornaam + " " + achternaam +
", jij bent " + leeftijd + " jaar oud.");

nieuwe eis: vraag ook naar leeftijd ✔

goed abstractie niveau afhankelijk van


gebruik nu


gebruik nu

gebruik later

Web applicaties in
Java/Seam

Data: Hibernate
@Entity
public class Blog {
protected String _title = "";
public String getTitle() {
return _title;
}
public void setTitle(String value) {
_title = value;
}
@ManyToOne
protected User _author;
public User getAuthor() {
return _author;
}
public void setAuthor(User author) {
_title = value;
}
@OneToMany(mappedBy="_blog",
targetEntity=BlogEntry.class)
@Cascade(...)
protected List<BlogEntry> _entries;
public List<BlogEntry> getEntries() {
return _entries;
}
public void setEntries(List<BlogEntry> entries) {
_entries = entries;
}
}

View: JSF
<html ...> ... <body> ...
<h:form>
<table>
<tr><td><h:outputText value="Title: "/></td>
<td><h:inputText value="#{editBlogEntry.e.title}" /></td>
</tr><tr>
<td><h:outputText value="Created: "/></td>
<td><rich:calendar value="#{editBlogEntry.e.created}"
popup="true" datePattern="dd/MM/yyyy" .../></td>
</tr><tr>
<td><h:outputText value="Content: "/></td>
<td><h:inputTextarea value="#{editBlogEntry.e.content}"/></td>
</tr><tr>
<td><h:outputText value="Status: "/></td>
<td><h:selectOneMenu value="#{editBlogEntry.e.status}">
<s:selectItems value="#{editBlogEntry.blogEntryStatusList}"
var="blogEntryStatus" label="#{blogEntryStatus.name}" />
<s:convertEntity/>
</h:selectOneMenu></td>
</tr>
</table>
<h:actionLink action=”#{editBlogEntry.save()}”/>
</h:form>
... </body> </html>

Controller
@Stateful @Name(“editBlogEntry”)
public class EditBlogEntry {
...
@In @Out
private BlogEntry e;

public void setE(e) {
this.e = e;
}

public BlogEntry getE() {
return this.e;
}

public void save() {
em.persist(e);
}
...
}

Conﬁguratie
<?xml version="1.0" ?>
<web-app ...>
<context-param>
<param-name>facelets.LIBRARIES</param-name>
<param-value>/WEB-INF/blog.taglib.xml</param-value>
</context-param>
<filter>
<filter-name>Seam Filter</filter-name>
<filter-class>org.jboss.seam.servlet.SeamFilter</filter-class>
</filter>
<filter>
<filter-name>UrlRewriteFilter</filter-name>
<filter-class>org.tuckey.web.filters.urlrewrite.UrlRewriteFilter</filter-class>
<init-param>
<param-name>logLevel</param-name>
<param-value>WARN</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>Seam Filter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>UrlRewriteFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<servlet>
<servlet-name>Faces Servlet</servlet-name>
<servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet>
<servlet-name>Seam Resource Servlet</servlet-name>
<servlet-class>org.jboss.seam.servlet.SeamResourceServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Faces Servlet</servlet-name>
<url-pattern>*.seam</url-pattern>
</servlet-mapping>
...
</web-app>

allemaal hetzelfde

Gebruiker
maken
wijzigen
verwijderen
koppelen

allemaal hetzelfde

Gebruiker Bericht
maken
wijzigen
verwijderen
koppelen

allemaal hetzelfde

Gebruiker Bericht
maken maken
wijzigen wijzigen
verwijderen verwijderen
koppelen koppelen

allemaal hetzelfde

Gebruiker Bericht Reactie
maken maken
wijzigen wijzigen
verwijderen verwijderen
koppelen koppelen

allemaal hetzelfde

maken maken maken
wijzigen wijzigen wijzigen
verwijderen verwijderen verwijderen
koppelen koppelen koppelen

allemaal hetzelfde

maken maken maken
wijzigen wijzigen wijzigen
verwijderen verwijderen verwijderen
koppelen koppelen koppelen

boiler plate code

Data
@Entity
public class Blog {
return _title;
}
_title = value;
}
@ManyToOne
public User getAuthor() {
return _author;
}
public void setAuthor(User author) {
_title = value;
}
@Cascade(...)
return _entries;
}
public void
setEntries(List<BlogEntry> entries) {
_entries = entries;
}
}

Data
@Entity
public class Blog {
return _title;
}
_title = value;
}
@ManyToOne
public User getAuthor() { entity Blog {
return _author; author -> User (inverse=User.blogs)
} title :: String
public void setAuthor(User author) { entries <> Set<BlogEntry>
_title = value; }
}
@Cascade(...)
return _entries;
}
public void
setEntries(List<BlogEntry> entries) {
_entries = entries;
}
}

<html ...> ... <body> ...
Pagina’s
<h:form>
<table>
<tr><td><h:outputText value="Title: "/></td> @Stateful @Name(“editBlogEntry”)
<td><h:inputText value="#{editBlogEntry.e.title}" /></td> public class EditBlogEntry {
</tr><tr> ...
<td><h:outputText value="Created: "/></td> @In @Out
<td><rich:calendar value="#{editBlogEntry.e.created}" private BlogEntry e;
popup="true" datePattern="dd/MM/yyyy" .../></td> public void setE(e) {
</tr><tr> this.e = e;
<td><h:outputText value="Content: "/></td> }
</tr><tr> public BlogEntry getE() {
<td><h:outputText value="Status: "/></td> return this.e;
<td><h:selectOneMenu value="#{editBlogEntry.e.status}"> }
var="blogEntryStatus" label="#{blogEntryStatus.name}" /> em.persist(e);
<s:convertEntity/> }
</h:selectOneMenu></td> ...
</tr> }
</table>
</h:form>
... </body> </html>

<html ...> ... <body> ...
Pagina’s
<h:form>
<table>
</tr><tr> ...
</tr> }
</table>
</h:form>
... </body> </html>

define page editBlogEntry(e : BlogEntry) {
form{
table{
row{ "Title: " input(e.title) }
row{ "Created: " input(e.created) }
row{ "Content: " input(e.content) }
row{ "Status: " input(e.status) }
action("Save", save())
}
}
action save() {
e.save();
return blogEntry(e);
}
}

<html ...> ... <body> ...
Pagina’s
<h:form>
<table>
</tr><tr> ...
</tr> }
</table>
</h:form>
... </body> </html>

define page editBlogEntry(e : BlogEntry) {
derive editPage from e
}

WebDSL code

WebDSL compiler

Java applicatie
(Java, JSF, Hibernate)

entity User {
username :: String
password :: Secret
}

entity Update {
user -> User
date :: DateTime
text :: Text
}

entity User {
username :: String
password :: Secret
}

entity Update {
user -> User
date :: DateTime
text :: Text
}

define page home() {
for(u : Update) {
output(u.user.username) ": " output(u.text)
spacer
}
}

header{ "Twitr" }
spacer
for(u : Update) {
spacer
}
"(C) Zef Hemel"
}

define page login() {
header{ "Twitr" }
spacer
var u : User

form {
"Login: " input(u)
action("Login", login())

action login() {
session.user := u;
return home();
}
}
spacer
"(C) Zef Hemel"
}

define template main() {
header{ "Twitr" }
spacer
body()
"(C) Zef Hemel"
}

main()
define body() {
for(u : Update) {
spacer
}
}
}

WebDSL code

Template expander

WebDSL compiler

Java applicatie
(Java, JSF, Hibernate)

template expander
main()
define body()
for(u : Update) {
spacer
}
}
}

header{ "Twitr" }
spacer
for(u : Update) {
spacer
}
"(C) Zef Hemel"
}

maar...

JSF had ook al templates

WebDSL code

Template expander

WebDSL compiler

Java applicatie
templates (Java, JSF, Hibernate)

WebDSL code

Template expander

templates WebDSL compiler

Java applicatie

WebDSL code

herimplementeert
templates Template expander


Java applicatie

abstraction
inversion
WebDSL code

herimplementeert


Java applicatie

abstraction
inversion
WebDSL code

herimplementeert

templates WebDSL compiler slechte abstractie

Java applicatie

“All non-trivial
abstractions, to some
degree, are leaky.”
-- Joel Spolsky

abstracties verbergen implementatie


dat lukt eigenlijk nooit volledig



WebDSL templates



WebDSL templates
NFS/SMB



WebDSL templates
NFS/SMB
twee-dimensionale arrays



WebDSL templates
NFS/SMB
twee-dimensionale arrays
SQL

abstractie is essentieel
moeilijk

denk kritisch na
heb ik dit vaker gedaan?

denk kritisch na
heb ik dit vaker gedaan?
gaat iemand dit vaker doen?

Abstractie (Dutch)

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Abstractie (Dutch)