java8 stream/optional个人测试demo记录
备忘记录
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package cc.ash; import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; import java.util.ArrayList; import java.util.Comparator; import java.util.List; import java.util.Optional; import java.util.stream.Collectors; public class StreamTest { public static void main(String[] args) { ArrayList<Stu> stus = new ArrayList<>(); Stu a = new Stu("name-A", 17, 64, "A"); Stu b = new Stu("name-B", 20, 58, "B"); Stu c = new Stu("name-C", 27, 60, "C"); Stu d = new Stu("name-D", 24, 56, "D"); stus.add(a); stus.add(b); stus.add(c); stus.add(d); // streamOpt(stus); stus.add(null); optionalHandleClct(stus); optionalHandle(null); } public static void streamOpt(List<Stu> stuList) { stuList.stream() .filter(s -> s.getAge() > 19) .peek(o -> System.out.println(o.getName())) .sorted((x, y) -> x.getWeight() - y.getWeight())//.mapToInt(Stu::getWeight).sum(); .peek(o -> System.out.println(o.getName())) .map(Stu::getAlias) .peek(System.out::println) .collect(Collectors.toList()); stuList.stream() .filter(o -> o.getWeight() > 45 && o.getWeight() < 61) // .sorted((x, y) -> x.getWeight() - y.getWeight()) //默认升序、反转降序。体重相同在根据年龄排序 .sorted(Comparator.comparing(Stu::getWeight).reversed().thenComparing(Stu::getAge)) .forEach(per -> System.out.println(per.getName())); } public static int optionalHandle(Stu stu) { return Optional.ofNullable(stu).map(Stu::getAge).orElse(-1); // return stu == null ? -1 : stu.getAge(); //等价 // if(stu == null) { // System.out.println("无信息,日志输出,异常处理"); // return -1; // } // return stu.getAge(); } public static void optionalHandleClct(List<Stu> stu) { int sum = stu.stream().mapToInt(o -> Optional.ofNullable(o).map(Stu::getAge).orElse(-1)).sum(); System.out.println(sum); } } @AllArgsConstructor @NoArgsConstructor @Data class Stu { private String name; private int age; private int weight; private String alias; }
stream
https://blog.csdn.net/qq_20989105/article/details/81234175
lambda