簡介¶

• stream().collect()
• public final class java.util.stream.Collectors
• public interface java.util.stream.Collector
• static class CollectorImpl implements Collector
• 收集器(A)，可變
  • creation of a new result container ({@link #supplier()})。提供container
  • incorporating a new data element into a result container ({@link #accumulator()})。container對下一個element的操作
  • combining two result containers into one ({@link #combiner()})。container合併
  • performing an optional final transform on the container ({@link #finisher()})。container轉換型態
• reduce，不可變

內容¶

groupingBy¶

• groupingBy(Function, Collector)
• collect(Collectors.groupingBy(Student::getName))
• groupingBy(Function, Supplier, Collector)
• collect(Collectors.groupingBy(Student::getName, Collectors.counting()));
• groupingByConcurrent(Function)

partitioningBy¶

• partitioningBy(Predicate)
• collect(Collectors.partitioningBy(student -> student.getScore() >= 90));
• partitioningBy(Predicate, Collector)
• collect(Collectors.partitioningBy(student -> student.getScore() >= 90, Collectors.counting()));

參考資料¶