How to get minimum and maximum value from List of Objects using Java 8

Question

I have class like:

public class Test {
    private String Fname;
    private String Lname;
    private String Age;
    // getters, setters, constructor, toString, equals, hashCode, and so on
}

and a list like List<Test> testList filled with Test elements.

How can I get minimum and maximum value of age using Java 8?

Solution 1

To simplify things you should probably make your age Integer or int instead of Sting, but since your question is about String age this answer will be based on String type.

---

Assuming that String age holds String representing value in integer range you could simply map it to IntStream and use its IntSummaryStatistics like

IntSummaryStatistics summaryStatistics = testList.stream()
        .map(Test::getAge)
        .mapToInt(Integer::parseInt)
        .summaryStatistics();

int max = summaryStatistics.getMax();
int min = summaryStatistics.getMin();

Solution 2

max age:

   testList.stream()
            .mapToInt(Test::getAge)
            .max();

min age:

   testList.stream()
            .mapToInt(Test::getAge)
            .min();

Comments

[Brian Goetz]

No need for the double-map; just mapToInt(Test::getAge), the unboxing will be done for you.

[Pshemo]

@BrianGoetz Not quite. Notice that getAge returns String not int.

[Brian Goetz]

Who writes domain objects that store numbers in strings? Sheesh. :)

[Brian Goetz]

OK, but returning to the domain of useful, the point I was trying to make was: lambda conversion will do necessary adaptation like widening, boxing, casting, etc, to make up differences between the natural type of the lambda and the target type -- that one need not manually insert adaptations like unboxing.