Java Lambda
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2022-04-17 23:19:04
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该语法糖在jvm脚本语言Groovy/Scale已有很好的支持,Java从8.0才开始支持该特性。
/** * 基础Lambda表达式 * */ public static void testLambda() { String[] ss = { "hello", "world", "sun" }; List<String> list = Arrays.asList(ss); // 接口作为回调函数,C: typdef int (*func)(int,int) AddService func = (int a, int b) -> (a + b); func.add(20, 21); // 多条语句用{}包围 AddService func1 = (int a, int b) -> { System.out.println("count"); return (a + b); }; func1.add(20, 21); // 1.遍历 // forEach list.forEach((player) -> System.out.println(player)); // :: list.forEach(System.out::println); // 2.排序 Arrays.sort(ss, (String s1, String s2) -> (s1.compareTo(s2))); // 3.线程 new Thread(() -> System.out.println(Thread.currentThread().getName() + ">Say hello")).start(); Runnable th1 = () -> System.out.println(Thread.currentThread().getName() + ">Say world"); th1.run(); } /** * Stream lambda * 强大的filter条件过滤 */ public static void testStream() { // Programmer List<Person> progm = new ArrayList<Person>() { { add(new Person("Jarrod", "Pace", "PHP programmer", "male", 34, 1550)); add(new Person("Clarette", "Cicely", "PHP programmer", "female", 23, 1200)); add(new Person("Victor", "Channing", "PHP programmer", "male", 32, 1600)); add(new Person("Tori", "Sheryl", "PHP programmer", "female", 21, 1000)); add(new Person("Osborne", "Shad", "PHP programmer", "male", 32, 1100)); add(new Person("Rosalind", "Layla", "PHP programmer", "female", 25, 1300)); add(new Person("Fraser", "Hewie", "PHP programmer", "male", 36, 1100)); add(new Person("Quinn", "Tamara", "PHP programmer", "female", 21, 1000)); add(new Person("Alvin", "Lance", "PHP programmer", "male", 38, 1600)); add(new Person("Evonne", "Shari", "PHP programmer", "female", 40, 1800)); } }; // 定义filter Predicate<Person> ageFilter = (p) -> (p.getAge() > 21); // age>21 Predicate<Person> salaryFilter = (p) -> (p.getSalary() > 1000); // salary>1000 Predicate<Person> genderFilter = (p) -> ("female".equals(p.getGender())); // femail // 过滤年龄大于21岁且月薪大于$1,000以上的2名女程序员 progm.stream() .filter(ageFilter) .filter(salaryFilter) .filter(genderFilter) .limit(2) // 只取2条记录 .forEach((p) -> System.out.printf("%s %s; ", p.getFirstname(), p.getLastname())); // 根据姓排序,将结果输出至list List<Person> sortprogm = progm .stream() .sorted( (p,p2) -> (p.getFirstname().compareTo(p2.getFirstname()))) .limit(2) .collect( Collectors.toList() ); // 过滤工资最低的程序员 Person per = progm .stream() .min( (p,p2) -> (p.getSalary() - p2.getSalary()) ) .get(); /// map/reduce lambda表达式不可或缺两组函数 // map --> 将姓添加至set Set<String> set = progm .stream() .map(Person::getFirstname) .collect( Collectors.toSet() ); // reduce --> 所有工资的总和 int total = progm .stream() .map( Person::getSalary ) .reduce( 0, (a,b) -> a+b ); // 数组最大最小值,总和,平均值等汇总 List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); IntSummaryStatistics stats = numbers .stream() .mapToInt((x) -> x) .summaryStatistics(); }
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