/**
     * 过滤集合中不符合条件的元素
     */
    @Test
    public void testfilter(){
        List<String> stringList = Arrays.asList("abc", "", "bc", "def", "abcd", "", "jkl");
        List<String> aList = stringList.stream().filter(str -> str.contains("a")).collect(Collectors.toList());
        aList.forEach(System.err::println);
    }

    /**
     *去重
     */
    @Test
    public void testDistinct(){
        List<String> stringList = Arrays.asList("abc", "", "bc", "def", "abcd", "", "jkl","jkl");
        List<String> distinctStr = stringList.stream().distinct().collect(Collectors.toList());
        distinctStr.forEach(System.out::println);
        //--------------------------------
        Product prod1 = new Product(1L, 1, new BigDecimal("15.5"), "面包", "零食");
        Product prod2 = new Product(2L, 2, new BigDecimal("20"), "饼干", "零食");
        Product prod3 = new Product(2L, 2, new BigDecimal("20"), "饼干", "零食");
        ArrayList<Product> proList = Lists.newArrayList(prod1, prod2, prod3);
        List<Product> distinctProList = proList.stream().distinct().collect(Collectors.toList());
        distinctProList.forEach(System.out::println);
    }

    /**
     * limit(n)获取流中的前n个元素
     */
    @Test
    public void testLimit(){
        List<String> stringList = Arrays.asList("abc", "", "bc", "def", "abcd", "", "jkl","jkl");
        List<String> limitStr = stringList.stream().limit(3).collect(Collectors.toList());
        System.out.println(limitStr);
    }

    /**
     * skip(n)
     */
    @Test
    public void testSkip(){
        List<String> stringList = Arrays.asList("abc", "", "bcd", "def", "abcd", "", "jkl","jkl");
        List<String> skipStrList = stringList.stream().skip(2).collect(Collectors.toList());
        System.out.println(skipStrList);
    }

    /**
     * map() 接收一个函数作为参数，这个函数会被应用到每个元素上，并将其映射成为一个新的元素
     */
    @Test
    public void testMap(){
        List<String> stringList = Arrays.asList("abc", "", "bcd", "def", "abcd", "", "jkl","jkl");
        List<String> mapStrList = stringList.stream().map(str -> str.concat("_map")).collect(Collectors.toList());
        System.out.println(mapStrList);
    }

    @Test
    public void testSorted(){
        List<String> stringList = Arrays.asList("abc", "", "bcd", "def", "abcd", "", "jkl","jkl");
        List<String> sortedStrList = stringList.stream().sorted().collect(Collectors.toList());
        System.out.println(sortedStrList);
    }

    /**
     * collect():将流转换为其他形式 list set map
     */
    @Test
    public void testCollect(){
        List<String> stringList = Arrays.asList("abc", "", "bcd", "def", "abcd", "", "jkl","jkl");
        Set<String> collectSet = stringList.stream().collect(Collectors.toSet());
        System.out.println(collectSet);
    }

    /**
     * 将流中元素反复结合起来得到一个结果
     */
    @Test
    public void testReduce(){
        List<String> stringList = Arrays.asList("abc", "", "bcd", "def", "abcd", "", "jkl","jkl");
        Optional<String> reduce = stringList.stream().reduce((acc, item) -> {return acc + item;});
        if (reduce.isPresent()) System.out.println(reduce.get());
    }

    /**
     * 将流中元素反复结合起来得到一个结果
     */
    @Test
    public void testCount(){
        List<String> stringList = Arrays.asList("abc", "", "bcd", "def", "abcd", "", "jkl","jkl");
        long count = stringList.stream().count();
        System.out.println(count);
    }