Question

问题就像标题一样简单。如何在Groovy中检查该对象是列表或集合或数组？但找不到一种简单的检查方法。有什么想法吗？

Answer 1

List是Collection，因此检查不是互斥的：

def foo = ...
boolean isCollection = foo instanceof Collection
boolean isList = foo instanceof List
boolean isSet = foo instanceof Set
boolean isArray = foo != null && foo.getClass().isArray()

Answer 2

我不知道您是否需要区分Collection，List和Array，或者只是想知道对象是否是这些类型的任何。如果是后者，你可以使用它：

boolean isCollectionOrArray(object) {    
    [Collection, Object[]].any { it.isAssignableFrom(object.getClass()) }
}

// some tests
assert isCollectionOrArray([])
assert isCollectionOrArray([] as Set)
assert isCollectionOrArray([].toArray())
assert !isCollectionOrArray("str")

在Groovy控制台中运行上面的代码，以确认其行为与宣传的一样

Answer 3

If you are looking for a Groovy way, look at in operator. It is actually a combination of Class.isAssignableFrom(Class<?>) and Class.isInstance(Object) meaning that you can use it to test classes as well as objects.

// Test classes
assert ArrayList in Collection
assert ArrayList in List
assert HashSet in Collection
assert HashSet in Set

// Test objects
def list = [] as ArrayList
def set = [] as HashSet

assert list in Collection
assert list in List
assert set in Collection
assert set in Set

Testing if an object is an array may be tricky. I would recommend @BurtBeckwith's approach.

def array = [].toArray()

assert array.getClass().isArray()

Answer 4

我用它来“对象化”一个对象，如果它已经是一个集合，那么它将返回一个副本，否则将其包装在一个列表中。因此，您无需在处理时检查它，它始终是一个集合。

def arrayfy = {[] + it ?: [it]}
def list = arrayfy(object) // will be always a list

Answer 5

只需使用instanceof运算符并检查对象是否是java.util.Collection的实例

Answer 6

通常，您希望使用duck typing检查其行为。

def foo = someMethod()
if (foo.metaClass.respondsTo('each')) {
  foo.each {println it}
}

如何在Groovy中检查该对象是列表或集合或数组？

6 个答案: