建造模式

原文地址：http://leihuang.org/2014/11/09/Builder-Pattern/

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

当构造函数的参数非常多时，并且有多个构造函数时，情况如下：

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. 下面还有一种解决方法叫javabean模式:

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!).详见：JavaBean Pattern

下面介绍一种更好的方法，就是今天的主题:建造模式

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;  }}

注意到现在Pizza是一个immutable class，所以它是线程安全的。又因为每一个Builder's setter方法都返回一个Builder对象，所以可以串联起来调用。如下

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

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2014-11-09 18:21:17

Brave，Happy，Thanksgiving !