Java8-Stream-No.10

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import java.util.Arrays;import java.util.IntSummaryStatistics;import java.util.List;import java.util.Map;import java.util.StringJoiner;import java.util.stream.Collector;import java.util.stream.Collectors;public class Streams10 {    static class Person {        String name;        int age;        Person(String name, int age) {            this.name = name;            this.age = age;        }        @Override        public String toString() {            return name;        }    }    public static void main(String[] args) {        List<Person> persons =            Arrays.asList(                new Person("Max", 18),                new Person("Peter", 23),                new Person("Pamela", 23),                new Person("David", 12));//        test1(persons);//        test2(persons);//        test3(persons);//        test4(persons);//        test5(persons);//        test6(persons);//        test7(persons);//        test8(persons);        test9(persons);    }    private static void test1(List<Person> persons) {        List<Person> filtered =            persons                .stream()                .filter(p -> p.name.startsWith("P"))                .collect(Collectors.toList());        System.out.println(filtered);    // [Peter, Pamela]    }    private static void test2(List<Person> persons) {        Map<Integer, List<Person>> personsByAge = persons            .stream()            .collect(Collectors.groupingBy(p -> p.age));        personsByAge            .forEach((age, p) -> System.out.format("age %s: %s\n", age, p));        // age 18: [Max]        // age 23:[Peter, Pamela]        // age 12:[David]    }    private static void test3(List<Person> persons) {        Double averageAge = persons            .stream()            .collect(Collectors.averagingInt(p -> p.age));        System.out.println(averageAge);     // 19.0    }    private static void test4(List<Person> persons) {        IntSummaryStatistics ageSummary =            persons                .stream()                .collect(Collectors.summarizingInt(p -> p.age));        System.out.println(ageSummary);        // IntSummaryStatistics{count=4, sum=76, min=12, average=19,000000, max=23}    }    private static void test5(List<Person> persons) {        String names = persons            .stream()            .filter(p -> p.age >= 18)            .map(p -> p.name)            .collect(Collectors.joining(" and ", "In Germany ", " are of legal age."));        System.out.println(names);        // In Germany Max and Peter and Pamela are of legal age.    }    private static void test6(List<Person> persons) {        Map<Integer, String> map = persons            .stream()            .collect(Collectors.toMap(                p -> p.age,                p -> p.name,                (name1, name2) -> name1 + ";" + name2));        System.out.println(map);        // {18=Max, 23=Peter;Pamela, 12=David}    }    private static void test7(List<Person> persons) {        Collector<Person, StringJoiner, String> personNameCollector =            Collector.of(                () -> new StringJoiner(" | "),          // supplier                (j, p) -> j.add(p.name.toUpperCase()),  // accumulator                (j1, j2) -> j1.merge(j2),               // combiner                StringJoiner::toString);                // finisher        String names = persons            .stream()            .collect(personNameCollector);        System.out.println(names);  // MAX | PETER | PAMELA | DAVID    }    private static void test8(List<Person> persons) {        Collector<Person, StringJoiner, String> personNameCollector =            Collector.of(                () -> {                    System.out.println("supplier");                    return new StringJoiner(" | ");                },                (j, p) -> {                    System.out.format("accumulator: p=%s; j=%s\n", p, j);                    j.add(p.name.toUpperCase());                },                (j1, j2) -> {                    System.out.println("merge");                    return j1.merge(j2);                },                j -> {                    System.out.println("finisher");                    return j.toString();                });        String names = persons            .stream()            .collect(personNameCollector);        System.out.println(names);  // MAX | PETER | PAMELA | DAVID    }    private static void test9(List<Person> persons) {        Collector<Person, StringJoiner, String> personNameCollector =            Collector.of(                () -> {                    System.out.println("supplier");                    return new StringJoiner(" | ");                },                (j, p) -> {                    System.out.format("accumulator: p=%s; j=%s\n", p, j);                    j.add(p.name.toUpperCase());                },                (j1, j2) -> {                    System.out.println("merge");                    return j1.merge(j2);                },                j -> {                    System.out.println("finisher");                    return j.toString();                });        String names = persons            .parallelStream()            .collect(personNameCollector);        System.out.println(names);  // MAX | PETER | PAMELA | DAVID    }}
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