Java Lambda

 

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();
}

 

参考链接：

​​Java lambda表达式入门​​