Design Mode: construction mode

Design Mode: construction mode

 

Creational Model

 

The generation of objects consumes system resources, so how to efficiently produce, manage, and operate objects has always been a topic worth discussing. The Creational model is related to the establishment of objects, the pattern under this classification provides some guiding principles and design directions. The list below all belongs to the Creational model.

• Simple Factory mode Abstract Factory mode Builder mode Factory Method mode Prototype mode Singleton mode Registry of Singleton Mode Problems

  The builder pattern is a good choice when designing classes whose constructors or static factories wowould have more than a handful of parameters.

  When there are many constructor parameters and multiple constructor functions, the following is the case:

  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 following is a solution called the javabean mode:

  Pizza pizza = new Pizza(12);pizza.setCheese(true);pizza.setPepperoni(true);pizza.setBacon(true);

   

  Javabeans make a class mutable even if it is not strictly necessary. So javabeans require an extra effort in handling thread-safety (an immutable class is always thread safety !). For details, see JavaBean Pattern.

  Build mode to solve this problem

  Public class Pizza {// required private final int size; // optional 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; // this parameter is set to 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 an immutable class, so it is thread-safe. Because every Builder's setter method returns a Builder object, it can be called in tandem. As follows:

  Pizza pizza = new Pizza.Builder(12)                       .cheese(true)                       .pepperoni(true)                       .bacon(true)                       .build();

   

  As we can see above, the construction mode gives users greater freedom and can choose any parameter.