8 Advanced Stream API Tips You Should Know

Java Streams API was introduced with Java 8. It allowed us to write clean, concise and readable code.

Here are 8 coding tips related to Streams API that you should use to enhance your development experience.

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1. Group and Transform in One Pass

Old Code

Map<String, List<String>> grouped = list.stream()
    .collect(Collectors.groupingBy(
        s -> s.substring(0, 1)));

for (Map.Entry<String, List<String>> e : grouped.entrySet()) {
    e.setValue(e.getValue().stream().map(String::toUpperCase).collect(Collectors.toList()));
}

Refactored Code

Map<String, List<String>> grouped = list.stream()
    .collect(Collectors.groupingBy(
        s -> s.substring(0, 1),
        Collectors.mapping(String::toUpperCase, Collectors.toList())));

Using teeing() Collector for Dual Accumulation

This method is available in Java 12+. It avoids double iterations with sum() and average() separately, as shown in the below code.

Code: Get Sum and Average in one Pass

Map.Entry<Integer, Double> result =…