整型处理

IntStream

求1-100中的偶数之和

        int result = IntStream.rangeClosed(1, 100)

                .filter(a -> a % 2 == 0)

                .sum();

        System.out.println(result);

int[] 与 Integer[] 转换

        int[] intArray = {1,2,3,4,5};

        Integer[] integers = Arrays.stream(intArray)

                //each boxed to an {@code Integer}.

                // 将每个int转成Integer

                .boxed()

                .toArray(Integer[]::new);

        System.out.println(Arrays.toString(integers));

字符串处理

join方法

        String[] str = {"hello", "world", "fonxian"};

        String s = String.join(",", str);

        System.out.println(s);

集合处理

去掉List中的重复元素

List<String> words = Arrays.asList("a", "b", "c", "d", "a", "b");

        words.stream()

                .distinct()

                .collect(Collectors.toList())

                .forEach(System.out::println);

接口

默认实现

interface Animal{

    void move();

    // 默认实现

    default void eat(){

        System.out.println("eat");

    }

}

class Dog implements Animal{

    @Override

    public void move() {

    }

}

class Cat implements Animal{

    @Override

    public void move() {

    }