Design mode: Construction mode

Original address: http://leihuang.org/2014/12/03/builder/

Creational mode

The production of objects needs to consume system resources, so how to produce, manage and manipulate objects efficiently is always a subject to be discussed, the creational model is related to the establishment of objects, and the model under this classification gives some guiding principles and the direction of design. Listed below are all belong to the creational mode

• Simple Factory Mode
• Abstract Factory Mode
• Builder mode
• Factory method Mode
• Prototype mode
• Singleton mode
• Registry of Singleton Mode

Problems that arise

The builder pattern is a good choice when designing classes whose constructors or static factories would has more than a Handful of parameters.

When the parameters of the constructor are very long and there are multiple constructors, the situation is as follows:

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. Here's another workaround called JavaBean mode:

Pizza Pizza = new Pizza (n);p Izza.setcheese (True);p Izza.setpepperoni (True);p Izza.setbacon (true);

Javabeans make a class mutable even if it's not strictly necessary. So JavaBeans require a extra effort in handling Thread-safety (an immutable class are always thread safety!). See: JavaBean Pattern

Build mode to solve the problem

<span style= "Font-weight:normal;"    >public class Pizza {//mandatory 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;        Because size is required, the parameter set to the constructor is 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 to New Pizza (this);        }} private Pizza (Builder builder) {size = Builder.size; Cheese = Builder.cheese;        Pepperoni = Builder.pepperoni;    Bacon = Builder.bacon; }}</span>

Note that pizza is now a immutable class, so it is thread-safe. And because each builder's setter method returns a builder object, it can be called in series. As follows

Pizza Pizza = new Pizza.builder (n). Cheese (true). Pepperoni (true).                       build ();

By the above we can know that the construction mode, gives the user greater freedom, can be optional parameters.

2014-11-09 18:21:17

Brave,happy,thanksgiving!

Design mode: Construction mode