A sister example of counting the number of instances of uppercase letters this example will count the number of lower case letters within a phrase using java 8 and guava.
Using java 8 we will calculate the number of lower case letters. Starting with a String we will call chars() which will return a IntStream. Next we will filter out any lower case letters by passing a java 8 predicate Character::isLowerCase. Finally we will use the stream terminal operation count to find the total number of instances.
This snippet will use guava to determine the total number of lower case letters in a String. You can think of CharMatcher as a set of characters so when we use CharMatcher.JAVALOWERCASE it means any lower case letters. The retainFrom function will remove all non-matching characters or all non lower case values.