When should I use a constructor and when should I use static method?
Can you explain above with small snippet? I skimmed through a few threads but I'm still not clear with this.
解决方案
Use a public constructor when you only ever want to return a new object that type and you want simplicity.
A good example is StringBuilder as it's mutable and you are likely to want a new object each time.
public String toString() {
StringBuilder sb = new StringBuilder();
// append fields to the sb
return sb.toString();
}
Use a static factor method when you might want to re-use objects (esp if immutable), you might want to return a sub-class or you want descriptice construction. A good example is EnumSet which has a number of static factories which do different things even though some have the same arguments.
EnumSet.noneOf(RetentionPolicy.class);
// has the same arguments, but is not the same as
EnumSet.allOf(RetentionPolicy.class);
In this case, using a static factory makes it clear what the difference between these two ways of construction the set.
Also EnumSet can return two different implementations, one optimised for enums with a small number of values (<= 64) RegularEnumSet and another for many values called JumboEnumSet
