Java8新特性——lambda函数式编程

一、遍历循环

 /**
  * @author jiaqing.xu@hand-china.com
  * @version 1.0
  * @name
  * @description 循环遍历
  * @date 2018/7/13
  */
 public class test1 {
     public static void main(String[] args) {
         String[] atp = {
                 "b",
                 "a",
                 "c",
                 "d",
                 "e",
                 "f",
                 "g",
                 "h"};
         List<String> players = Arrays.asList(atp);

         // 直接对list进行循环输出
         players.forEach((p) -> System.out.print(p + "; "));
         System.out.println("\n");
         //循环输出带换行符，方法引用使用双冒号
         players.forEach(System.out::println);

     }
 }

二、数据过滤

 /**
  * @author jiaqing.xu@hand-china.com
  * @version 1.0
  * @name
  * @description 数据过滤
  * @date 2018/7/13
  */
 public class test2 {
     public static void main(String args[]) {
         List languages = Arrays.asList("Java", "Scala", "C++", "Haskell", "Lisp");
         //打印以J开头的字符串
         System.out.println("Print all languages :");
         filter1(languages, (str) -> str.toString().startsWith("J"));
         //条件恒为假
         System.out.println("Print no language : ");
         filter(languages, (str) -> false);
         //混合过滤条件
         System.out.println("...");
         filter3(languages);
     }

     //传统过滤
     public static void filter(List<String> names, Predicate condition) {
         for (String name : names) {
             if (condition.test(name)) {
                 System.out.println(name + " ");
             }
         }
     }

     //以lambda方式过滤
     public static void filter1(List names, Predicate condition) {
         names.stream().filter((name) -> (condition.test(name))).forEach((name) -> System.out.println(name + " "));
     }

     public static void filter3(List names) {
         //第一个规则是以J开头
         Predicate<String> startsWithJ = (n) -> n.startsWith("J");
         //第二个规则是长度为4
         Predicate<String> fourLetterLong = (n) -> n.length() == 4;
         names.stream().filter(startsWithJ.and(fourLetterLong)).forEach((n) -> System.out.println("The result is:" + n));
     }
 }

三、Map和Reduce函数计算

 /**
  * @author jiaqing.xu@hand-china.com
  * @version 1.0
  * @name
  * @description map和reduce 函数计算
  * @date 2018/7/13
  */
 public class test3 {
     public static void main(String[] args) {
         // With Lambda expression:
         //Map用于函数计算，为集合中的每个元素增加一定的数值
         List costBeforeTax = Arrays.asList(100, 200, 300, 400, 500);
         costBeforeTax.stream().map((cost) -> (Integer) cost + .12 * (Integer) cost).forEach(System.out::println);

         //reduce 类似sql中的sum avg count
         List costBeforeTax2 = Arrays.asList(100, 200, 300, 400, 500);
         Object bill = costBeforeTax2.stream()
                 .map((cost) -> (Integer) cost + .12 * (Integer) cost)
                 .reduce((sum, cost) -> (Double) sum + (Double) cost)
                 .get();
         System.out.println("Total : " + bill);

         //应用函数将字符串转换为大写形式并用逗号拼接
         List<String> G7 = Arrays.asList("USA", "Japan", "France", "Germany", "Italy", "U.K.", "Canada");
         String G7Countries = G7.stream()
                 .map(x -> x.toUpperCase())
                 .collect(Collectors.joining(", "));
         System.out.println(G7Countries);

         //计算list中最大值、最小值和平均值
         List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23, 29);
         IntSummaryStatistics stats = primes.stream().mapToInt((x) -> x)
                 .summaryStatistics();
         System.out.println("Highest prime number in List : " + stats.getMax());
         System.out.println("Lowest prime number in List : " + stats.getMin());
         System.out.println("Sum of all prime numbers : " + stats.getSum());
         System.out.println("Average of all prime numbers : " + stats.getAverage());
     }
 }