标签：des style http io color ar os sp java
原文地址：http://leihuang.net/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();
2014-11-09 18:21:17
Brave，Happy，Thanksgiving !
标签：des style http io color ar os sp java
原文地址：http://blog.csdn.net/speedme/article/details/41120097
