Java 8: Calculate average, sum, maximum, minimum and count of elements of a list

The easiest way probably is to get the summary statistics of the list through stream first. Get all the values, then, from the summary statistics. Below is an example for a integer list. The same logic applies to all other type of numbers.

List<Integer> intList = Arrays.asList(123, 886, 43, 25, 33, 89);

IntSummaryStatistics intStat = intList.stream()
            .mapToInt ( i -> i)
            .summaryStatistics();

double average = intStat.getAverage();
long sum = intStat.getSum();
long count = intStat.getCount();
int max = intStat.getMax();
int min = intStat.getMin();

Of course, if you just want to get the sum or find the maximum, you can do it like below.

int sum = intList.stream()
           .mapToInt(i -> i)
           .sum();

int max = intList.stream()
           .mapToInt(i -> i)
           .max()
           .orElse(0);

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