Lambda Expressions and Method References - Java: A Beginner's Guide - page 674

The output is shown here:
In the program, pay special attention to this line:
Here, a reference to the static method isPrime( ) is passed as the first argument to
numTest( ) . This works because isPrime is compatible with the IntPredicate functional
interface. Thus, the expression MyIntPredicates::isPrime evaluates to a reference to an
object in which isPrime( ) provides the implementation of test( ) in IntPredicate . The oth-
er two calls to numTest( ) work in the same way.
Method References to Instance Methods
A reference to an instance method on a specific object is create by this basic syntax:
objRef :: methodName
As you can see, the syntax is similar to that used for a static method, except that an object
reference is used instead of a class name. Thus, the method referred to by the method ref-
erence operates relative to objRef . The following program illustrates this point. It uses the
same IntPredicate interface and test( ) method as the previous program. However, it cre-
ates a class called MyIntNum , which stores an int value and defines the method isFactor(
) , which determines if the value passed is a factor of the value stored by the MyIntNum in-
stance. The main( ) method then creates two MyIntNum instances. It then calls numTest(
) , passing in a method reference to the isFactor( ) method and the value to be checked. In
each case, the method reference operates relative to the specific object.