CODEWITHSUNDEEP
groovynull
res1
res1

Reputation: 3660

Why don't I get a NullPointerException in Groovy in this case?

I have this test code:

def test = null

test.each {  }

Why don't I get any exception?

Upvotes: 14

Views: 5515

Answers (2)

Dónal
Dónal

Reputation: 187389

The implementation of each tries to call the iterator method of it's target in a null-safe fashion. If each is called on a null object, or an object without an iterator method, nothing happens.

I haven't seen the source code, but it could look something like this§

Object each(Closure closure) {

  if (this?.respondsTo("iterator")) {

    def iterator = this.iterator()

    while (iterator.hasNext() {
      def item = iterator.next()
      closure(item)
    }
  }
  return this
}

§ In reality, this method is probably written in Java rather than Groovy

Upvotes: 16

Jared
Jared

Reputation: 39903

A null value when using the each closure is the same as a collection with 0 elements. If you have the code

def test=null
test.each {println "In closure with value "+it}

The print statement won't execute. If you change test to

def test=[1,2,3]

you will get output.

Upvotes: 3

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