Lambda练习

　　虽然java8已经很普遍了，但是它的其中之一特性——Lambda我很少用，甚至是不会用。今天查资料时，无意发现一遍博客，写的不错，我就练习了会！

一、相关博文

Java8之Lambda表达式概念篇：https://www.jianshu.com/p/67ebee04b2b3

Java8之Stream类：https://www.jianshu.com/p/c53eb31752c4

二、涉及到的实体类

public class User {

    @Setter
    @Getter
    String userName;

    @Setter
    @Getter
    String passWord;

    @Override
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof User)) {
            return false;
        }
        User user = (User) obj;
        Boolean flag = Objects.equals(userName, user.userName) &&
                Objects.equals(passWord, user.passWord);
        return flag;
    }

    @Override
    public int hashCode() {
        return Objects.hash(passWord, userName);
    }

    public User(String userName, String passWord) {
        this.userName = userName;
        this.passWord = passWord;
    }

    @Override
    public String toString() {
        return "User{" +
                "userName='" + userName + '\'' +
                ", passWord='" + passWord + '\'' +
                '}';
    }

}

三、各种功能

static List<User> userList = new ArrayList<User>() {
        {
            add(new User("a", "b"));
            add(new User("a1", "b1"));
            add(new User("a222", "b2"));
            add(new User("a", "bb"));
            add(new User("a", "bbc"));
            add(new User("a3", "b1"));
            add(new User("a44", "b2"));
        }
    };

　　1、forEach两种遍历方式　　

@Test
    public void forEachTest() {
        System.out.println("forEach遍历方式一");
        userList.forEach(s -> System.out.print(s + " "));
        System.out.println("forEach遍历方式二");
        userList.forEach(System.out::println);
    }

　　2、排序

@Test
    public void sortTest() {
        String[] players = {"1", "3", "2", "0"};
        System.out.println("排序前");
        List<String> list = Arrays.asList(players);
        list.forEach(s -> System.out.print(s + " "));

        Arrays.sort(players, new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                return o1.compareTo(o2);
            }
        });
        System.out.println("\n排序后");
        List<String> list1 = Arrays.asList(players);
        list1.forEach(s -> System.out.print(s + " "));
    }

　　3、调用setter、getter　

@Test
    public void setterGetterTest() {
        userList.forEach(s -> s.setUserName(s.getUserName() + " --123-- "));
        userList.forEach(System.out::print);
    }

　　4、过滤器

@Test
    public void filterTest() {
        userList.stream()
                .filter(p -> p.getUserName().equals("a"))
                .limit(1)
                .forEach(p -> System.out.println(p.getPassWord() + " "));

        userList.stream()
                .filter(p -> p.getUserName().equals("a"))
                .forEach(p -> System.out.println(p.getPassWord() + " "));
    }

　　5、stream处理

@Test
    public void streamTest() {
        List<User> userList1 = userList.stream()
                .sorted((p1, p2) -> p1.getUserName().compareTo(p2.getUserName()))
                .limit(5)
                .collect(Collectors.toList());
        userList1.forEach(p -> System.out.println(p + " "));

        System.out.println("");

        userList.stream()
                .sorted((p1, p2) -> p1.getUserName().compareTo(p2.getUserName()))
                .limit(10)
                .collect(Collectors.toList())
                .forEach(System.out::println);
    }

　　6、max　　

@Test
    public void maxTest() {
        User maxUser = userList.stream()
                .max((p1, p2) -> p1.getUserName().length() - p2.getUserName().length())
                .get();
        System.out.println(maxUser);
    }

　　7、min　

@Test
    public void minTest() {
        User minUser = userList.stream()
                .min((p1, p2) -> p1.getUserName().length() - p2.getUserName().length())
                .get();
        System.out.println(minUser);
    }

　　8、sum　　

@Test
    public void sumTest() {
        int totalSalary = userList.parallelStream()
                .mapToInt(p -> p.getUserName().length())
                .sum();
        System.out.println(totalSalary);
        // 输出：14
    }

　　9、将list转化为String　

@Test
    public void toStringTest() {
        String strUser = userList.stream()
                .map(User::getUserName)
                .collect(Collectors.joining(";"));
        System.out.println(strUser);
        // 输出：a;a1;a222;a;a;a3;a44
    }

　　10、将list转化为Set

@Test
    public void toSetTest() {
        Set<String> setUser = userList.stream()
                .map(User::getUserName)
                .collect(Collectors.toSet());
        setUser.forEach(s -> System.out.print(s + " "));
        // 输出：a1 a44 a a3 a222
    }

　　11、将list转化为TreeSet

@Test
    public void toTreeSetTest() {
        TreeSet<String> treeSet = userList.stream()
                .map(User::getUserName)
                .collect(Collectors.toCollection(TreeSet::new));
        treeSet.forEach(s -> System.out.print(s + " "));
        //输出：a a1 a222 a3 a44
    }

　　12、统计　

@Test
    public void test11() {
        List<Integer> intNum = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        IntSummaryStatistics summaryStatistics = intNum.stream()
                .mapToInt(x -> x).summaryStatistics();

        System.out.println("总数：" + summaryStatistics.getCount());
        System.out.println("平均：" + summaryStatistics.getAverage());
        System.out.println("最大：" + summaryStatistics.getMax());
        System.out.println("最小：" + summaryStatistics.getMin());
        System.out.println("总计：" + summaryStatistics.getSum());
    }

　　13、线程

@Test
    public void threadTest() {
        // 继承Thread的形式
        new Thread(() -> System.out.println("我是线程的run方法"))
                .start();
        // 实现runable的形式
        Runnable r2 = () -> System.out.println("我也是线程的run方法");
        r2.run();
    }

 

 

 

参考：https://blog.csdn.net/qq_37722734/article/details/82148490