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How to replace if else loop for object creation

i have to instantiate objects based on some if conditions. e.g. if this then create this object else if this then create this object etc....how should i go about dealing with this prob. I am sure there must be a smater way out.
[234 byte] By [j2eeprofessionala] at [2007-10-2 19:04:25]
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# 1
Please read the Factory Pattern... That will tell how you how effectively you can code for this scenario
redwina at 2007-7-13 20:43:44 > top of Java-index,Other Topics,Patterns & OO Design...
# 2
You should also check the reflection framework. Through this framework, you can load classes at runtime with a String containing the classname.
ractoca at 2007-7-13 20:43:44 > top of Java-index,Other Topics,Patterns & OO Design...
# 3

how about having a Map of Condition to Class, and instantiate the class? so rather than having

public MyType getNewObject(String id) {

if ( id.equals("first") return new First();

if ( id.equals("second") return new Second();

...

}

you'd have something like (VERY oversimplified)

private Map<String, Class> map;

...

public MyType getNewObject(String id) {

Class clazz = map.get(id);

// there will be some exceptions to handle here IRL

return (MyType) clazz.newInstance();

}

the Map gets populated by a static initializer or in the constructor or wherever. Or, you could take this further still by adopting - as the other guy said - some more reflection, that way you could populate the Map from a config file, and have yourself the beginnings of a pluggable application

private Map<String, String> map;

...

public MyType getNewObject(String id) {

Class clazz = Class.forName(map.get(id));

return (MyType) clazz.newInstance();

}

georgemca at 2007-7-13 20:43:44 > top of Java-index,Other Topics,Patterns & OO Design...
# 4

just musing, something to chew on :)

import java.util.*;

interface Life

{

}

class Adam extends Dna implements Life

{

private static Map Helix = new HashMap();

public static Map GetHelix() {

return Adam.Helix;

}

static {

Adam.Helix.put( "father", "aaa" );

Adam.Helix.put( "mother", "bbb" );

};

protected Adam() {

}

}

class Eve extends Dna implements Life

{

private static Map Helix = new HashMap();

public static Map GetHelix() {

return Eve.Helix;

}

static {

Eve.Helix.put( "father", "ccc" );

Eve.Helix.put( "mother", "ddd" );

};

protected Eve() {

}

}

class Dna

{

public Dna( Map h ) {

this.m = h;

}

public Dna() {

}

private static Map Pool = new HashMap();

static {

Pool.put( Eve.GetHelix(), new Eve() );

Pool.put( Adam.GetHelix(), new Adam() );

};

public static Life Create( Dna s ) {

Iterator it = Dna.Pool.keySet().iterator();

while( it.hasNext() ) {

Map k = (Map) it.next();

if( Dna.Match( k, s ) ) {

return (Life) Dna.Pool.get( k );

}

}

return null;

}

private static boolean Match( Map c, Dna d ) {

Iterator it = d.GetHelix().keySet().iterator();

while( it.hasNext() ) {

Object k = it.next();

Object v = d.GetHelix().get( k );

if( ! c.containsKey( k )

|| ! c.containsValue( v ) ) {

return false;

}

}

return true;

}

private static Map m = new HashMap();

public static Map GetHelix() {

return m;

}

}

public class DoGyrotcaF

{

public static void main( String[] args ) {

Map m = new HashMap();

m.put( "father", "123" );

m.put( "mother", "abc" );

Dna dna = new Dna( m );

System.out.println( "c: " + Dna.Create( dna ) );

m.clear();

m.put( "father", "aaa" );

m.put( "mother", "bbb" );

dna = new Dna( m );

System.out.println( "c: " + Dna.Create( dna ) );

m.clear();

m.put( "father", "ccc" );

m.put( "mother", "ddd" );

dna = new Dna( m );

System.out.println( "c: " + Dna.Create( dna ) );

}

}

mchan0a at 2007-7-13 20:43:44 > top of Java-index,Other Topics,Patterns & OO Design...
# 5
The notorious "plug-in" pattern traces back. Typically, I do it via reflection. In the case of static binding, like the "onclick" selection of instantance, no mapping is even needed.
valjoka at 2007-7-13 20:43:44 > top of Java-index,Other Topics,Patterns & OO Design...
# 6
I mean no mapping is needed either
valjoka at 2007-7-13 20:43:44 > top of Java-index,Other Topics,Patterns & OO Design...
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