Expression Language (EL) - Introducing Java EE 7 - page 42

Table 3-1. ( continued )

Operation Description

firstOrDefault Iterates over the source elements, and if a predicate function is specified, then the first

element returning a true result is yielded. Otherwise, if no predicate function is specified,
the firstOrDefault operator simply returns the first element in the collection.
If no element matches the predicate or if the source sequence is empty, a null is
returned.
Example: employees.firstOrDefault()

last Iterates over the source elements, and if a predicate function is specified, then the last

element returning a true result is yielded. Otherwise, if no predicate function is specified,
the last operator simply returns the last element in the collection.
An InvalidOperationException is thrown if no element matches the predicate or if the
source collection is empty.
Example: employees.last()

lastOrDefault Iterates over the source elements, and if a predicate function is specified, then the last

element returning a true result is yielded. If no predicate function is specified, the
lastOrDefault operator simply returns the last element in the collection.
If no element matches the predicate or if the source sequence is empty, a null is
returned.
Example: employees.lastOrDefault()

single Iterates over the source elements and returns the single element that returns true from

the predicate function. If no predicate function is specified, the single operator simply
returns the single element of the collection.
An InvalidOperationException is thrown if the source sequence is empty or contains no
matching element or more than one matching element.
Example: employees.single()

singleOrDefault Iterates over the source elements and returns the single element that returns true

from the predicate function. If no predicate function is specified, the singleOrDefault
operator simply returns the single element of the collection.
An InvalidOperationException is thrown if the source sequence contains more than
one matching element. If no element matches the predicate or if the source sequence is
empty, null is returned.
Example: employees.singleOrDefault()

elementAt The List.get() method is used to obtain the element at the specified index if the

collection is a List . Otherwise, the elements in the collection are iterated index number
of times, and the element found at the specified position is returned.
An IndexOutOfBoundException is thrown if the index is less than zero or greater than or
equal to the number of elements in the collection.
Example: employees.elementAt(12)

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