Effective java 笔记1

Effective Java 创建对象之 static factory method

1：优先考虑static factory method,然后再考虑constructor

    1.1 static factory method 的优点
    1.1.1 static factory method 相对constructor 更容易命名，尤其是当static factory method 和 constructor 方法数量多的时候，static factory method 容易命名的好处更加突出，更加容易理解方法的用途。

    1.1.2 获取对象时，constructor每次都生成新的对象， 而static factory method却不需要

    1.1.3 constructor只能返回当前类的对象，而static factory method 可以返回当前类的对象或 当前类的子类对象
   
    1.1.4 创建泛型对象时，static factory method 可以减少所用的词（所使用语句的长度）
   
1.2 static factory method 的缺点

1.2.1 最大的缺点是：如果没有public或者protected constructor的类，该类无法被继承。
1.2.2 有时候多个static factory method 会让程序员迷惑，不知道使用哪个方法获取对象那个比较好
对于第二条，遵循以下规则就可以极大程度上减弱它的影响：

• valueOf—
Returns an instance that has, loosely speaking, the same value as its
parameters. Such static factories are effectively type-conversion methods.

• of—A concise alternative to valueOf, popularized by EnumSet

• getInstance—Returns an instance that is described by the parameters but
cannot be said to have the same value. In the case of a singleton, getInstance
takes no parameters and returns the sole instance.

• newInstance—Like getInstance, except that newInstance guarantees that
each instance returned is distinct from all others.

• getType—Like getInstance, but used when the factory method is in a different
class. Type indicates the type of object returned by the factory method.

• newType—Like newInstance, but used when the factory method is in a different
class. Type indicates the type of object returned by the factory method.