问题
While reading some groovy code of another developer I encountered the following definition:
def foo=[:]
What does it mean?
回答1:
[:] is shorthand notation for creating a Map.
You can also add keys and values to it:
def foo = [bar: 'baz']
回答2:
[:] creates an empty Map. The colon is there to distinguish it from [], which creates an empty List.
This groovy code:
def foo = [:]
is roughly equivalent to this java code:
Object foo = new java.util.LinkedHashMap();
回答3:
Quoting the doc:
Notice that
[:]is the empty map expression.
... which is the only Map with size() returning 0. ) By itself, it's rarely useful, but you can add values into this Map, of course:
def emptyMap = [:]
assert emptyMap.size() == 0
emptyMap.foo = 5
assert emptyMap.size() == 1
assert emptyMap.foo == 5
来源：https://stackoverflow.com/questions/22865107/what-does-mean-in-groovy