When would you use the Builder Pattern

Question

What are some common  real world examples of using the Builder Pattern   What does it buy you   Why not just use a Factory Pattern

User · Answer

I used builder in home-grown messaging library  The library core was receiving data from the wire  collecting it with Builder instance  then  once Builder decided it ve got everything it needed to create a Message instance  Builder GetMessage   was constructing a message instance using the data collected from the wire

User · Answer

Another advantage of the builder is that if you have a Factory  there is still some coupling in you code  because for the Factory to work  it has to know all the objects it can possibly create  If you add another object that could be created  you will have to modify the factory class to include him  This happens in the Abstract Factory as well   With the builder  on the other hand  you just have to create a new concrete builder for this new class  The director class will stay the same  because it receives the builder in the constructor   Also  there are many flavors of builder  Kamikaze Mercenary s gives another one

User · Answer

For a multi-threaded problem  we needed a complex object to be built up for each thread  The object represented the data being processed  and could change depending on the user input   Could we use a factory instead  Yes  Why didn t we  Builder makes more sense I guess    Factories are used for creating different types of objects that are the same basic type  implement the same interface or base class     Builders build the same type of object over and over  but the construction is dynamic so it can be changed at runtime

User · Answer

Below are some reasons arguing for the use of the pattern and example code in Java  but it is an implementation of the Builder Pattern covered by the Gang of Four in Design Patterns  The reasons you would use it in Java are also applicable to other programming languages as well   As Joshua Bloch states in Effective Java  2nd Edition       The builder pattern is a good choice when designing classes whose constructors or static factories would have more than a handful of parameters    We ve all at some point encountered a class with a list of constructors where each addition adds a new option parameter   Pizza int size                  Pizza int size  boolean cheese              Pizza int size  boolean cheese  boolean pepperoni              Pizza int size  boolean cheese  boolean pepperoni  boolean bacon            This is called the Telescoping Constructor Pattern  The problem with this pattern is that once constructors are 4 or 5 parameters long it becomes difficult to remember the required order of the parameters as well as what particular constructor you might want in a given situation   One alternative you have to the Telescoping Constructor Pattern is the JavaBean Pattern where you call a constructor with the mandatory parameters and then call any optional setters after    Pizza pizza   new Pizza 12   pizza setCheese true   pizza setPepperoni true   pizza setBacon true     The problem here is that because the object is created over several calls it may be in an inconsistent state partway through its construction  This also requires a lot of extra effort to ensure thread safety   The better alternative is to use the Builder Pattern   public class Pizza     private int size    private boolean cheese    private boolean pepperoni    private boolean bacon     public static class Builder         required     private final int size         optional     private boolean cheese   false      private boolean pepperoni   false      private boolean bacon   false       public Builder int size          this size   size             public Builder cheese boolean value          cheese   value        return this             public Builder pepperoni boolean value          pepperoni   value        return this             public Builder bacon boolean value          bacon   value        return this             public Pizza build           return new Pizza this                private Pizza Builder builder        size   builder size      cheese   builder cheese      pepperoni   builder pepperoni      bacon   builder bacon          Note that Pizza is immutable and that parameter values are all in a single location  Because the Builder s setter methods return the Builder object they are able to be chained   Pizza pizza   new Pizza Builder 12                          cheese true                          pepperoni true                          bacon true                          build      This results in code that is easy to write and very easy to read and understand  In this example  the build method could be modified to check parameters after they have been copied from the builder to the Pizza object and throw an IllegalStateException if an invalid parameter value has been supplied  This pattern is flexible and it is easy to add more parameters to it in the future  It is really only useful if you are going to have more than 4 or 5 parameters for a constructor  That said  it might be worthwhile in the first place if you suspect you may be adding more parameters in the future   I have borrowed heavily on this topic from the book Effective Java  2nd Edition by Joshua Bloch  To learn more about this pattern and other effective Java practices I highly recommend it

User · Answer

The key difference between a builder and factory IMHO  is that a builder is useful when you need to do lots of things to build an object  For example imagine a DOM  You have to create plenty of nodes and attributes to get your final object  A factory is used when the factory can easily create the entire object within one method call   One example of using a builder is a building an XML document  I ve used this model when building HTML fragments for example I might have a Builder for building a specific type of table and it might have the following methods  parameters are not shown    BuildOrderHeaderRow   BuildLineItemSubHeaderRow   BuildOrderRow   BuildLineItemSubRow     This builder would then spit out the HTML for me  This is much easier to read than walking through a large procedural method   Check out Builder Pattern on Wikipedia

User · Answer

You use it when you have lots of options to deal with   Think about things like jmock   m expects once         method  testMethod        with eq 1   eq 2        returns  someResponse      It feels a lot more natural and is   possible   There s also xml building  string building and many other things   Imagine if java util Map had put as a builder   You could do stuff like this   Map lt String  Integer gt  m   new HashMap lt String  Integer gt         put  a   1       put  b   2       put  c   3

User · Answer

For a multi-threaded problem  we needed a complex object to be built up for each thread  The object represented the data being processed  and could change depending on the user input   Could we use a factory instead  Yes  Why didn t we  Builder makes more sense I guess    Factories are used for creating different types of objects that are the same basic type  implement the same interface or base class     Builders build the same type of object over and over  but the construction is dynamic so it can be changed at runtime

User · Answer

For a multi-threaded problem  we needed a complex object to be built up for each thread  The object represented the data being processed  and could change depending on the user input   Could we use a factory instead  Yes  Why didn t we  Builder makes more sense I guess    Factories are used for creating different types of objects that are the same basic type  implement the same interface or base class     Builders build the same type of object over and over  but the construction is dynamic so it can be changed at runtime

User · Answer

Below are some reasons arguing for the use of the pattern and example code in Java  but it is an implementation of the Builder Pattern covered by the Gang of Four in Design Patterns  The reasons you would use it in Java are also applicable to other programming languages as well   As Joshua Bloch states in Effective Java  2nd Edition       The builder pattern is a good choice when designing classes whose constructors or static factories would have more than a handful of parameters    We ve all at some point encountered a class with a list of constructors where each addition adds a new option parameter   Pizza int size                  Pizza int size  boolean cheese              Pizza int size  boolean cheese  boolean pepperoni              Pizza int size  boolean cheese  boolean pepperoni  boolean bacon            This is called the Telescoping Constructor Pattern  The problem with this pattern is that once constructors are 4 or 5 parameters long it becomes difficult to remember the required order of the parameters as well as what particular constructor you might want in a given situation   One alternative you have to the Telescoping Constructor Pattern is the JavaBean Pattern where you call a constructor with the mandatory parameters and then call any optional setters after    Pizza pizza   new Pizza 12   pizza setCheese true   pizza setPepperoni true   pizza setBacon true     The problem here is that because the object is created over several calls it may be in an inconsistent state partway through its construction  This also requires a lot of extra effort to ensure thread safety   The better alternative is to use the Builder Pattern   public class Pizza     private int size    private boolean cheese    private boolean pepperoni    private boolean bacon     public static class Builder         required     private final int size         optional     private boolean cheese   false      private boolean pepperoni   false      private boolean bacon   false       public Builder int size          this size   size             public Builder cheese boolean value          cheese   value        return this             public Builder pepperoni boolean value          pepperoni   value        return this             public Builder bacon boolean value          bacon   value        return this             public Pizza build           return new Pizza this                private Pizza Builder builder        size   builder size      cheese   builder cheese      pepperoni   builder pepperoni      bacon   builder bacon          Note that Pizza is immutable and that parameter values are all in a single location  Because the Builder s setter methods return the Builder object they are able to be chained   Pizza pizza   new Pizza Builder 12                          cheese true                          pepperoni true                          bacon true                          build      This results in code that is easy to write and very easy to read and understand  In this example  the build method could be modified to check parameters after they have been copied from the builder to the Pizza object and throw an IllegalStateException if an invalid parameter value has been supplied  This pattern is flexible and it is easy to add more parameters to it in the future  It is really only useful if you are going to have more than 4 or 5 parameters for a constructor  That said  it might be worthwhile in the first place if you suspect you may be adding more parameters in the future   I have borrowed heavily on this topic from the book Effective Java  2nd Edition by Joshua Bloch  To learn more about this pattern and other effective Java practices I highly recommend it

User · Answer

I used builder in home-grown messaging library  The library core was receiving data from the wire  collecting it with Builder instance  then  once Builder decided it ve got everything it needed to create a Message instance  Builder GetMessage   was constructing a message instance using the data collected from the wire

User · Answer

Building on the previous answers  pun intended   an excellent real-world example is Groovy s built in support for Builders    Creating XML using Groovy s MarkupBuilder Creating XML using Groovy s StreamingMarkupBuilder Swing Builder SwingXBuilder   See Builders in the Groovy Documentation

User · Answer

Building on the previous answers  pun intended   an excellent real-world example is Groovy s built in support for Builders    Creating XML using Groovy s MarkupBuilder Creating XML using Groovy s StreamingMarkupBuilder Swing Builder SwingXBuilder   See Builders in the Groovy Documentation

User · Answer

I always disliked the Builder pattern as something unwieldy  obtrusive and very often abused by less experienced programmers  Its a pattern which only makes sense if you need to assemble the object from some data which requires a post-initialisation step  i e  once all the data is collected - do something with it   Instead  in 99  of the time builders are simply used to initialise the class members   In such cases it is far better to simply declare withXyz      type setters inside the class and make them return a reference to itself    Consider this   public class Complex        private String first      private String second      private String third       public String getFirst           return first              public void setFirst String first          this first first                        public Complex withFirst String first          this first first         return this              public Complex withSecond String second          this second second         return this              public Complex withThird String third          this third third         return this              Complex complex   new Complex         withFirst  first value         withSecond  second value         withThird  third value      Now we have a neat single class that manages its own initialization and does pretty much the same job as the builder  except that its far more elegant

User · Answer

Consider a restaurant  The creation of  today s meal  is a factory pattern  because you tell the kitchen  get me today s meal  and the kitchen  factory  decides what object to generate  based on hidden criteria   The builder appears if you order a custom pizza  In this case  the waiter tells the chef  builder   I need a pizza  add cheese  onions and bacon to it   Thus  the builder exposes the attributes the generated object should have  but hides how to set them

User · Answer

You use it when you have lots of options to deal with   Think about things like jmock   m expects once         method  testMethod        with eq 1   eq 2        returns  someResponse      It feels a lot more natural and is   possible   There s also xml building  string building and many other things   Imagine if java util Map had put as a builder   You could do stuff like this   Map lt String  Integer gt  m   new HashMap lt String  Integer gt         put  a   1       put  b   2       put  c   3

User · Answer

lt summary gt      Builder      lt  summary gt  public interface IWebRequestBuilder       IWebRequestBuilder BuildHost string host        IWebRequestBuilder BuildPort int port        IWebRequestBuilder BuildPath string path        IWebRequestBuilder BuildQuery string query        IWebRequestBuilder BuildScheme string scheme        IWebRequestBuilder BuildTimeout int timeout        WebRequest Build            lt summary gt      ConcreteBuilder  1      lt  summary gt  public class HttpWebRequestBuilder   IWebRequestBuilder       private string  host       private string  path   string Empty       private string  query   string Empty       private string  scheme    http        private int  port   80       private int  timeout   -1       public IWebRequestBuilder BuildHost string host                 host   host          return this             public IWebRequestBuilder BuildPort int port                 port   port          return this             public IWebRequestBuilder BuildPath string path                 path   path          return this             public IWebRequestBuilder BuildQuery string query                 query   query          return this             public IWebRequestBuilder BuildScheme string scheme                 scheme   scheme          return this             public IWebRequestBuilder BuildTimeout int timeout                 timeout   timeout          return this             protected virtual void BeforeBuild HttpWebRequest httpWebRequest               public WebRequest Build                 var uri    scheme            host          port          path          query           var httpWebRequest   WebRequest CreateHttp uri            httpWebRequest Timeout    timeout           BeforeBuild httpWebRequest            return httpWebRequest                lt summary gt      ConcreteBuilder  2      lt  summary gt  public class ProxyHttpWebRequestBuilder   HttpWebRequestBuilder       private string  proxy   null       public ProxyHttpWebRequestBuilder string proxy                 proxy   proxy             protected override void BeforeBuild HttpWebRequest httpWebRequest                httpWebRequest Proxy   new WebProxy  proxy                 lt summary gt      Director      lt  summary gt  public class SearchRequest        private IWebRequestBuilder  requestBuilder       public SearchRequest IWebRequestBuilder requestBuilder                 requestBuilder   requestBuilder             public WebRequest Construct string searchQuery                return  requestBuilder          BuildHost  ajax googleapis com            BuildPort 80           BuildPath  ajax services search web            BuildQuery  v 1 0 amp q     HttpUtility UrlEncode searchQuery            BuildScheme  http            BuildTimeout -1           Build               public string GetResults string searchQuery            var request   Construct searchQuery           var resp   request GetResponse             using  StreamReader stream   new StreamReader resp GetResponseStream                           return stream ReadToEnd                       class Program            lt summary gt          Inside both requests the same SearchRequest Construct string  method is used          But finally different HttpWebRequest objects are built           lt  summary gt      static void Main string   args                var request1   new SearchRequest new HttpWebRequestBuilder             var results1   request1 GetResults  IBM            Console WriteLine results1            var request2   new SearchRequest new ProxyHttpWebRequestBuilder  localhost 80             var results2   request2 GetResults  IBM            Console WriteLine results2

User · Answer

I used builder in home-grown messaging library  The library core was receiving data from the wire  collecting it with Builder instance  then  once Builder decided it ve got everything it needed to create a Message instance  Builder GetMessage   was constructing a message instance using the data collected from the wire

User · Answer

You use it when you have lots of options to deal with   Think about things like jmock   m expects once         method  testMethod        with eq 1   eq 2        returns  someResponse      It feels a lot more natural and is   possible   There s also xml building  string building and many other things   Imagine if java util Map had put as a builder   You could do stuff like this   Map lt String  Integer gt  m   new HashMap lt String  Integer gt         put  a   1       put  b   2       put  c   3

User · Answer

Consider a restaurant  The creation of  today s meal  is a factory pattern  because you tell the kitchen  get me today s meal  and the kitchen  factory  decides what object to generate  based on hidden criteria   The builder appears if you order a custom pizza  In this case  the waiter tells the chef  builder   I need a pizza  add cheese  onions and bacon to it   Thus  the builder exposes the attributes the generated object should have  but hides how to set them

User · Answer

lt summary gt      Builder      lt  summary gt  public interface IWebRequestBuilder       IWebRequestBuilder BuildHost string host        IWebRequestBuilder BuildPort int port        IWebRequestBuilder BuildPath string path        IWebRequestBuilder BuildQuery string query        IWebRequestBuilder BuildScheme string scheme        IWebRequestBuilder BuildTimeout int timeout        WebRequest Build            lt summary gt      ConcreteBuilder  1      lt  summary gt  public class HttpWebRequestBuilder   IWebRequestBuilder       private string  host       private string  path   string Empty       private string  query   string Empty       private string  scheme    http        private int  port   80       private int  timeout   -1       public IWebRequestBuilder BuildHost string host                 host   host          return this             public IWebRequestBuilder BuildPort int port                 port   port          return this             public IWebRequestBuilder BuildPath string path                 path   path          return this             public IWebRequestBuilder BuildQuery string query                 query   query          return this             public IWebRequestBuilder BuildScheme string scheme                 scheme   scheme          return this             public IWebRequestBuilder BuildTimeout int timeout                 timeout   timeout          return this             protected virtual void BeforeBuild HttpWebRequest httpWebRequest               public WebRequest Build                 var uri    scheme            host          port          path          query           var httpWebRequest   WebRequest CreateHttp uri            httpWebRequest Timeout    timeout           BeforeBuild httpWebRequest            return httpWebRequest                lt summary gt      ConcreteBuilder  2      lt  summary gt  public class ProxyHttpWebRequestBuilder   HttpWebRequestBuilder       private string  proxy   null       public ProxyHttpWebRequestBuilder string proxy                 proxy   proxy             protected override void BeforeBuild HttpWebRequest httpWebRequest                httpWebRequest Proxy   new WebProxy  proxy                 lt summary gt      Director      lt  summary gt  public class SearchRequest        private IWebRequestBuilder  requestBuilder       public SearchRequest IWebRequestBuilder requestBuilder                 requestBuilder   requestBuilder             public WebRequest Construct string searchQuery                return  requestBuilder          BuildHost  ajax googleapis com            BuildPort 80           BuildPath  ajax services search web            BuildQuery  v 1 0 amp q     HttpUtility UrlEncode searchQuery            BuildScheme  http            BuildTimeout -1           Build               public string GetResults string searchQuery            var request   Construct searchQuery           var resp   request GetResponse             using  StreamReader stream   new StreamReader resp GetResponseStream                           return stream ReadToEnd                       class Program            lt summary gt          Inside both requests the same SearchRequest Construct string  method is used          But finally different HttpWebRequest objects are built           lt  summary gt      static void Main string   args                var request1   new SearchRequest new HttpWebRequestBuilder             var results1   request1 GetResults  IBM            Console WriteLine results1            var request2   new SearchRequest new ProxyHttpWebRequestBuilder  localhost 80             var results2   request2 GetResults  IBM            Console WriteLine results2

User · Answer

The key difference between a builder and factory IMHO  is that a builder is useful when you need to do lots of things to build an object  For example imagine a DOM  You have to create plenty of nodes and attributes to get your final object  A factory is used when the factory can easily create the entire object within one method call   One example of using a builder is a building an XML document  I ve used this model when building HTML fragments for example I might have a Builder for building a specific type of table and it might have the following methods  parameters are not shown    BuildOrderHeaderRow   BuildLineItemSubHeaderRow   BuildOrderRow   BuildLineItemSubRow     This builder would then spit out the HTML for me  This is much easier to read than walking through a large procedural method   Check out Builder Pattern on Wikipedia

User · Answer

The key difference between a builder and factory IMHO  is that a builder is useful when you need to do lots of things to build an object  For example imagine a DOM  You have to create plenty of nodes and attributes to get your final object  A factory is used when the factory can easily create the entire object within one method call   One example of using a builder is a building an XML document  I ve used this model when building HTML fragments for example I might have a Builder for building a specific type of table and it might have the following methods  parameters are not shown    BuildOrderHeaderRow   BuildLineItemSubHeaderRow   BuildOrderRow   BuildLineItemSubRow     This builder would then spit out the HTML for me  This is much easier to read than walking through a large procedural method   Check out Builder Pattern on Wikipedia

User · Answer

While going through Microsoft MVC framework  I got a thought about builder pattern  I came across the pattern in the ControllerBuilder class  This class is to return the controller factory class  which is then used to build concrete controller   Advantage I see in using builder pattern is that  you can create a factory of your own and plug it into the framework     Tetha  there can be a restaurant  Framework  run by Italian guy  that serves Pizza  In order to prepare pizza Italian guy  Object Builder  uses Owen  Factory  with a pizza base  base class    Now Indian guy takes over the restaurant from Italian guy  Indian restaurant  Framework  servers dosa instead of pizza  In order to prepare dosa Indian guy  object builder  uses Frying Pan  Factory  with a Maida  base class   If you look at scenario  food is different way food is prepared is different  but in the same restaurant  under same framework   Restaurant should be build in such a way that it can support Chinese  Mexican or any cuisine  Object builder inside framework facilitates to plugin kind of cuisine you want  for example  class RestaurantObjectBuilder      IFactory  factory   new DefaultFoodFactory          This can be used when you want to plugin the     public void SetFoodFactory IFactory customFactory                factory   customFactory           public IFactory GetFoodFactory              return  factory

User · Answer

Consider a restaurant  The creation of  today s meal  is a factory pattern  because you tell the kitchen  get me today s meal  and the kitchen  factory  decides what object to generate  based on hidden criteria   The builder appears if you order a custom pizza  In this case  the waiter tells the chef  builder   I need a pizza  add cheese  onions and bacon to it   Thus  the builder exposes the attributes the generated object should have  but hides how to set them

User · Answer

NET StringBuilder class is a great example of builder pattern  It is mostly used to create a string in a series of steps  The final result you get on doing ToString   is always a string but the creation of that string varies according to what functions in the StringBuilder class were used  To sum up  the basic idea is to build complex objects and hide the implementation details of how it is being built

User · Answer

While going through Microsoft MVC framework  I got a thought about builder pattern  I came across the pattern in the ControllerBuilder class  This class is to return the controller factory class  which is then used to build concrete controller   Advantage I see in using builder pattern is that  you can create a factory of your own and plug it into the framework     Tetha  there can be a restaurant  Framework  run by Italian guy  that serves Pizza  In order to prepare pizza Italian guy  Object Builder  uses Owen  Factory  with a pizza base  base class    Now Indian guy takes over the restaurant from Italian guy  Indian restaurant  Framework  servers dosa instead of pizza  In order to prepare dosa Indian guy  object builder  uses Frying Pan  Factory  with a Maida  base class   If you look at scenario  food is different way food is prepared is different  but in the same restaurant  under same framework   Restaurant should be build in such a way that it can support Chinese  Mexican or any cuisine  Object builder inside framework facilitates to plugin kind of cuisine you want  for example  class RestaurantObjectBuilder      IFactory  factory   new DefaultFoodFactory          This can be used when you want to plugin the     public void SetFoodFactory IFactory customFactory                factory   customFactory           public IFactory GetFoodFactory              return  factory

User · Answer

I used builder in home-grown messaging library  The library core was receiving data from the wire  collecting it with Builder instance  then  once Builder decided it ve got everything it needed to create a Message instance  Builder GetMessage   was constructing a message instance using the data collected from the wire

User · Answer

Another advantage of the builder is that if you have a Factory  there is still some coupling in you code  because for the Factory to work  it has to know all the objects it can possibly create  If you add another object that could be created  you will have to modify the factory class to include him  This happens in the Abstract Factory as well   With the builder  on the other hand  you just have to create a new concrete builder for this new class  The director class will stay the same  because it receives the builder in the constructor   Also  there are many flavors of builder  Kamikaze Mercenary s gives another one

User · Answer

When I wanted to use the standard XMLGregorianCalendar for my XML to object marshalling of DateTime in Java  I heard a lot of comments on how heavy weight and cumbersome it was to use it  I was trying to comtrol the XML fields in the xs datetime structs to manage timezone  milliseconds  etc   So I designed a utility to build an XMLGregorian calendar from a GregorianCalendar or java util Date   Because of where I work I m not allowed to share it online without legal  but here s an example of how a client uses it  It abstracts the details and filters some of the implementation of XMLGregorianCalendar that are less used for xs datetime   XMLGregorianCalendarBuilder builder   XMLGregorianCalendarBuilder newInstance jdkDate   XMLGregorianCalendar xmlCalendar   builder excludeMillis   excludeOffset   build      Granted this pattern is more of a filter as it sets fields in the xmlCalendar as undefined so they are excluded  it still  builds  it  I ve easily added other options to the builder to create an xs date  and xs time struct and also to manipulate timezone offsets when needed   If you ve ever seen code that creates and uses XMLGregorianCalendar  you would see how this made it much easier to manipulate

User · Answer

I always disliked the Builder pattern as something unwieldy  obtrusive and very often abused by less experienced programmers  Its a pattern which only makes sense if you need to assemble the object from some data which requires a post-initialisation step  i e  once all the data is collected - do something with it   Instead  in 99  of the time builders are simply used to initialise the class members   In such cases it is far better to simply declare withXyz      type setters inside the class and make them return a reference to itself    Consider this   public class Complex        private String first      private String second      private String third       public String getFirst           return first              public void setFirst String first          this first first                        public Complex withFirst String first          this first first         return this              public Complex withSecond String second          this second second         return this              public Complex withThird String third          this third third         return this              Complex complex   new Complex         withFirst  first value         withSecond  second value         withThird  third value      Now we have a neat single class that manages its own initialization and does pretty much the same job as the builder  except that its far more elegant

User · Answer

For a multi-threaded problem  we needed a complex object to be built up for each thread  The object represented the data being processed  and could change depending on the user input   Could we use a factory instead  Yes  Why didn t we  Builder makes more sense I guess    Factories are used for creating different types of objects that are the same basic type  implement the same interface or base class     Builders build the same type of object over and over  but the construction is dynamic so it can be changed at runtime

User · Answer

NET StringBuilder class is a great example of builder pattern  It is mostly used to create a string in a series of steps  The final result you get on doing ToString   is always a string but the creation of that string varies according to what functions in the StringBuilder class were used  To sum up  the basic idea is to build complex objects and hide the implementation details of how it is being built

User · Answer

Building on the previous answers  pun intended   an excellent real-world example is Groovy s built in support for Builders    Creating XML using Groovy s MarkupBuilder Creating XML using Groovy s StreamingMarkupBuilder Swing Builder SwingXBuilder   See Builders in the Groovy Documentation

User · Answer

Building on the previous answers  pun intended   an excellent real-world example is Groovy s built in support for Builders    Creating XML using Groovy s MarkupBuilder Creating XML using Groovy s StreamingMarkupBuilder Swing Builder SwingXBuilder   See Builders in the Groovy Documentation

User · Answer

You use it when you have lots of options to deal with   Think about things like jmock   m expects once         method  testMethod        with eq 1   eq 2        returns  someResponse      It feels a lot more natural and is   possible   There s also xml building  string building and many other things   Imagine if java util Map had put as a builder   You could do stuff like this   Map lt String  Integer gt  m   new HashMap lt String  Integer gt         put  a   1       put  b   2       put  c   3

User · Answer

Consider a restaurant  The creation of  today s meal  is a factory pattern  because you tell the kitchen  get me today s meal  and the kitchen  factory  decides what object to generate  based on hidden criteria   The builder appears if you order a custom pizza  In this case  the waiter tells the chef  builder   I need a pizza  add cheese  onions and bacon to it   Thus  the builder exposes the attributes the generated object should have  but hides how to set them

User · Answer

When I wanted to use the standard XMLGregorianCalendar for my XML to object marshalling of DateTime in Java  I heard a lot of comments on how heavy weight and cumbersome it was to use it  I was trying to comtrol the XML fields in the xs datetime structs to manage timezone  milliseconds  etc   So I designed a utility to build an XMLGregorian calendar from a GregorianCalendar or java util Date   Because of where I work I m not allowed to share it online without legal  but here s an example of how a client uses it  It abstracts the details and filters some of the implementation of XMLGregorianCalendar that are less used for xs datetime   XMLGregorianCalendarBuilder builder   XMLGregorianCalendarBuilder newInstance jdkDate   XMLGregorianCalendar xmlCalendar   builder excludeMillis   excludeOffset   build      Granted this pattern is more of a filter as it sets fields in the xmlCalendar as undefined so they are excluded  it still  builds  it  I ve easily added other options to the builder to create an xs date  and xs time struct and also to manipulate timezone offsets when needed   If you ve ever seen code that creates and uses XMLGregorianCalendar  you would see how this made it much easier to manipulate

User · Answer

The key difference between a builder and factory IMHO  is that a builder is useful when you need to do lots of things to build an object  For example imagine a DOM  You have to create plenty of nodes and attributes to get your final object  A factory is used when the factory can easily create the entire object within one method call   One example of using a builder is a building an XML document  I ve used this model when building HTML fragments for example I might have a Builder for building a specific type of table and it might have the following methods  parameters are not shown    BuildOrderHeaderRow   BuildLineItemSubHeaderRow   BuildOrderRow   BuildLineItemSubRow     This builder would then spit out the HTML for me  This is much easier to read than walking through a large procedural method   Check out Builder Pattern on Wikipedia

[java] When would you use the Builder Pattern?

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