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<String> 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<String>() {      @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<String> predicate = n -> n.startsWith("N");    list_one.stream().filter(predicate).forEach(System.out::print);    List<Integer> list3 = new ArrayList<>();    list3.add(10);    list3.add(8);    list3.add(3);    list3.add(15);    list3.add(20);    Predicate<Integer> 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<String> 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<Integer> 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<String> names, Predicate<String> condition) {    names.stream().filter(name -> condition.test(name)).forEach(vo -> System.out.print(vo + " "));    System.out.println();  }}