java中Lambda常用场景代码实例

public class test18 {
  /**
   * lambda表达式的常用场景
   */
  @Test
  public void test() {
    List list_one = new ArrayList<>();
    list_one.add("NIKE");
    list_one.add("Addidas");
    /**
     * 用在匿名内部类里简写 ()->
     */
    new Thread(new Runnable() {
      @Override
      public void run() {
        System.out.println("do nothing");
      }
    }).start();
    new Thread(() -> System.out.println("do nothing")).start();
 
    //用在集合比较器里
    Collections.sort(list_one, new Comparator() {
      @Override
      public int compare(String o1, String o2) {
        return o1.compareTo(o2);
      }
    });
    Collections.sort(list_one, (o1, o2) -> o1.compareTo(o2));//正序
    Collections.sort(list_one, (o1, o2) -> -o1.compareTo(o2));//逆序
 
    //用在遍历集合 或操作集合中元素的时候
    list_one.forEach(System.out::println);
    List result = new ArrayList();
    list_one.stream().forEach(item -> result.add(item));
 
 
    System.out.println("--boundary--");
 
    //通过自定义filter方法 或者 集合.stream().filter(Predicate<>)
    filter(list_one, n -> n.startsWith("N"));
    filter(list_one, n -> true);
    filter(list_one, n -> false);
    filter(list_one, n -> n.length() > 5);
 
    Predicate predicate = n -> n.startsWith("N");
    list_one.stream().filter(predicate).forEach(System.out::print);
    List list3 = new ArrayList<>();
    list3.add(10);
    list3.add(8);
    list3.add(3);
    list3.add(15);
    list3.add(20);
    Predicate predicate1 = n -> Integer.valueOf(n) > 10;
 
    //用于map reduce中 此处先filter删选数据 然后执行map操作
    Double aDouble = list3.stream().filter(predicate1).map(vo -> vo * .12 + vo).reduce((sum, vo) -> sum + vo).get();
    System.out.println(aDouble);
 
    //stream()之后可以通过distinct()去重 也可以通过stream().collect(Collectors.toSet())去重 
    //Collector.joining(delimiter)通过定界符连接成字符串
    List list4 = new ArrayList<>();
    list4.add("Hello");
    list4.add("Boy");
    list4.add("How");
    list4.add("Are");
    list4.add("You");
    list4.add("You");
    list4.stream().distinct().collect(Collectors.toList()).forEach(System.out::print);
    System.out.println(list4.stream().map(x -> x.toUpperCase()).collect(Collectors.joining(", ")));
 
    /**
     * 通过mapTOInt() mapToDouble() mapToLong() 然后summarStatistics() 可以获得 IntSummaryStatistics 这个类的实例
     * 然后调用它的getSum() getAverage() getCount() getMax() getMin()方法
     */
    List list5 = Arrays.asList(1, 3, 4, 5, 6, 7, 10, 23);
    IntSummaryStatistics intSummaryStatistics = list5.stream().mapToInt(x -> x).summaryStatistics();
    System.out.println(intSummaryStatistics.getSum());
    System.out.println(intSummaryStatistics.getAverage());
    System.out.println(intSummaryStatistics.getCount());
    System.out.println(intSummaryStatistics.getMax());
    System.out.println(intSummaryStatistics.getMin());
  }
 
  public void filter(List names, Predicate condition) {
    names.stream().filter(name -> condition.test(name)).forEach(vo -> System.out.print(vo + " "));
    System.out.println();
  }
}