Builder Pattern)

1. Concept

Separates a complex build from its representation so that different representations can be created during the same build process. [Construction and representation separation, different representations are constructed in the same way]

Difference from Abstract Factory: In the builder mode, there is a mentor who manages the builder. the user is in contact with the mentor, and the mentor contacts the builder to get the product. That is, the construction mode can enforce a step-by-step construction process.

The construction mode encapsulates complex internal creation in the Internal. For external callers, they only need to pass in the builder and construction tool. The caller does not need to care about how the internal creation is finished.

For example, there are many components in a car, such as many parts, wheels, steering wheel, engine, and other small parts. But how can we assemble these components into a car, this assembly process is also very complex (requires good assembly technology). The Builder mode is to separate parts from assembly.

2. UML diagram

3.Code

     Public   Interface Builder {
 Void Buildparta ();
 Void Buildpartb ();
  Void Buildpartc ();

Product getresult ();
}

 // Specific construction tool 
 Public   Class Concretebuilder Implements Builder {
Part parta, partb, partc;

 Public   Void Buildparta (){
 // Here is how to build the parta code  
 };
 Public   Void Buildpartb (){
 //  Here is how to build the partb code  
 };
 Public   Void Buildpartc (){
 //  Here is how to build the partb code  
 };
 Public Product getresult (){
 //  Returns the final assembly result.  
 };
}

 // Builder 
 Public   Class Director {
 Private Builder;

 Public Director (Builder ){
 This . Builder = builder;
}
 Public   Void Construct (){
Builder. buildparta ();
Builder. buildpartb ();
Builder. buildpartc ();
}
}


 Public   Interface Product {}
 Public   Interface Part {}
 

The following describes how to call builder:
Concretebuilder =NewConcretebuilder ();
Director dire=NewDirector (builder );

Director. Construct ();
Product = builder. getresult ();
 

4. Application scenarios

This mode is used in Java applications.