JDK1.8 Lambda

1.模拟Model

/**
 * Author:JsonLu
 * DateTime:16/12/8 14:01
 * Email:jsonlu@qq.com
 * Desc:
 */
public class Person {

    private String firstName, lastName, job, gender;
    private int salary, age;

    public Person(String firstName, String lastName, String job,
                  String gender, int age, int salary)       {
        this.firstName = firstName;
        this.lastName = lastName;
        this.gender = gender;
        this.age = age;
        this.job = job;
        this.salary = salary;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public int getSalary() {
        return salary;
    }

    public void setSalary(int salary) {
        this.salary = salary;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

2.操作示例

import java.util.*;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * Author:JsonLu
 * DateTime:16/12/8 11:00
 * Email:jsonlu@qq.com
 * Desc:
 */
public class Lambda {

    /**
     * Lambda  Map操作
     */
    public void LambdaMap() {
        TreeMap<String, Integer> map = new TreeMap();
        map.put("abc", 1233);
        map.put("aBc", 1233);
        map.put("aBC", 1233);
        map.put("Abc", 1233);
        map.put("ABc", 1233);
        map.put("ABC", 1233);
        for (Map.Entry entry : map.entrySet()) {
            System.out.println(entry.getKey() + "=" + entry.getValue());
        }
        map.forEach((key, value) -> System.out.println(key));
    }

    /**
     * Lambda List操作
     */
    public void LambdaList() {
        List<String> list = Arrays.asList("a", "b", "B");
        // 使用 lambda 表达式以及函数操作(functional operation)
        list.forEach((ll) -> System.out.print(ll + "; "));
        // 在 Java 8 中使用双冒号操作符(double colon operator)
        list.forEach(System.out::println);
    }

    /**
     * Lambda 线程操作
     */
    public void LambdaThread() {
        // 1.1使用匿名内部类
        new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("Hello world !");
            }
        }).start();
        // 1.2使用 lambda expression
        new Thread(() -> System.out.println("Hello world !")).start();
        // 2.1使用匿名内部类
        Runnable race1 = new Runnable() {
            @Override
            public void run() {
                System.out.println("Hello world !");
            }
        };
        // 2.2使用 lambda expression
        Runnable race2 = () -> System.out.println("Hello world !");
        // 直接调用 run 方法(没开新线程哦!)
        race1.run();
        race2.run();
    }

    /**
     * Lambda 集合操作
     */
    public void LambdaComparator() {
        String[] players = {"Rafael Nadal", "Novak Djokovic",
                "Stanislas Wawrinka", "David Ferrer",
                "Roger Federer", "Andy Murray",
                "Tomas Berdych", "Juan Martin Del Potro",
                "Richard Gasquet", "John Isner"};

        // 1.1 使用匿名内部类根据 name 排序 players
        Arrays.sort(players, new Comparator<String>() {
            @Override
            public int compare(String s1, String s2) {
                return (s1.compareTo(s2));
            }
        });

        // 1.2 使用 lambda expression 排序 players
        Comparator<String> sortByName = (String s1, String s2) -> (s1.compareTo(s2));
        Arrays.sort(players, sortByName);
        // 1.3 也可以采用如下形式:
        Arrays.sort(players, (String s1, String s2) -> (s1.compareTo(s2)));

        // 1.1 使用匿名内部类根据 surname 排序 players
        Arrays.sort(players, new Comparator<String>() {
            @Override
            public int compare(String s1, String s2) {
                return (s1.substring(s1.indexOf(" ")).compareTo(s2.substring(s2.indexOf(" "))));
            }
        });

        // 1.2 使用 lambda expression 排序,根据 surname
        Comparator<String> sortBySurname = (String s1, String s2) -> (s1.substring(s1.indexOf(" ")).compareTo(s2.substring(s2.indexOf(" "))));
        Arrays.sort(players, sortBySurname);

        // 1.3 或者这样,怀疑原作者是不是想错了,括号好多...
        Arrays.sort(players, (String s1, String s2) -> (s1.substring(s1.indexOf(" ")).compareTo(s2.substring(s2.indexOf(" ")))));

        // 2.1 使用匿名内部类根据 name lenght 排序 players
        Arrays.sort(players, new Comparator<String>() {
            @Override
            public int compare(String s1, String s2) {
                return (s1.length() - s2.length());
            }
        });

        // 2.2 使用 lambda expression 排序,根据 name lenght
        Comparator<String> sortByNameLenght = (String s1, String s2) -> (s1.length() - s2.length());
        Arrays.sort(players, sortByNameLenght);

        // 2.3 or this
        Arrays.sort(players, (String s1, String s2) -> (s1.length() - s2.length()));

        // 3.1 使用匿名内部类排序 players, 根据最后一个字母
        Arrays.sort(players, new Comparator<String>() {
            @Override
            public int compare(String s1, String s2) {
                return (s1.charAt(s1.length() - 1) - s2.charAt(s2.length() - 1));
            }
        });

        // 3.2 使用 lambda expression 排序,根据最后一个字母
        Comparator<String> sortByLastLetter =
                (String s1, String s2) ->
                        (s1.charAt(s1.length() - 1) - s2.charAt(s2.length() - 1));
        Arrays.sort(players, sortByLastLetter);

        // 3.3 or this
        Arrays.sort(players, (String s1, String s2) -> (s1.charAt(s1.length() - 1) - s2.charAt(s2.length() - 1)));
    }

    /**
     * Stream 操作
     */
    public void Stream() {
        List<Person> javaProgrammers = new ArrayList<Person>() {
            {
                add(new Person("Elsdon", "Jaycob", "Java programmer", "male", 43, 2000));
                add(new Person("Tamsen", "Brittany", "Java programmer", "female", 23, 1500));
                add(new Person("Floyd", "Donny", "Java programmer", "male", 33, 1800));
                add(new Person("Sindy", "Jonie", "Java programmer", "female", 32, 1600));
                add(new Person("Vere", "Hervey", "Java programmer", "male", 22, 1200));
                add(new Person("Maude", "Jaimie", "Java programmer", "female", 27, 1900));
                add(new Person("Shawn", "Randall", "Java programmer", "male", 30, 2300));
                add(new Person("Jayden", "Corrina", "Java programmer", "female", 35, 1700));
                add(new Person("Palmer", "Dene", "Java programmer", "male", 33, 2000));
                add(new Person("Addison", "Pam", "Java programmer", "female", 34, 1300));
            }
        };

        List<Person> phpProgrammers = new ArrayList<Person>() {
            {
                add(new Person("Jarrod", "Pace", "PHP programmer", "male", 34, 1550));
                add(new Person("Clarette", "Cicely", "PHP programmer", "female", 23, 1200));
                add(new Person("Victor", "Channing", "PHP programmer", "male", 32, 1600));
                add(new Person("Tori", "Sheryl", "PHP programmer", "female", 21, 1000));
                add(new Person("Osborne", "Shad", "PHP programmer", "male", 32, 1100));
                add(new Person("Rosalind", "Layla", "PHP programmer", "female", 25, 1300));
                add(new Person("Fraser", "Hewie", "PHP programmer", "male", 36, 1100));
                add(new Person("Quinn", "Tamara", "PHP programmer", "female", 21, 1000));
                add(new Person("Alvin", "Lance", "PHP programmer", "male", 38, 1600));
                add(new Person("Evonne", "Shari", "PHP programmer", "female", 40, 1800));
            }
        };
        System.out.println("所有程序员的姓名:");
        javaProgrammers.forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));
        phpProgrammers.forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

        System.out.println("给程序员加薪 5% :");
        Consumer<Person> giveRaise = e -> e.setSalary(e.getSalary() / 100 * 5 + e.getSalary());

        javaProgrammers.forEach(giveRaise);
        phpProgrammers.forEach(giveRaise);

        System.out.println("下面是月薪超过 $1,400 的PHP程序员:");
        phpProgrammers.stream()
                .filter((p) -> (p.getSalary() > 1400))
                .forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

        // 定义 filters
        Predicate<Person> ageFilter = (p) -> (p.getAge() > 25);
        Predicate<Person> salaryFilter = (p) -> (p.getSalary() > 1400);
        Predicate<Person> genderFilter = (p) -> ("female".equals(p.getGender()));

        System.out.println("下面是年龄大于 24岁且月薪在$1,400以上的女PHP程序员:");
        phpProgrammers.stream()
                .filter(ageFilter)
                .filter(salaryFilter)
                .filter(genderFilter)
                .forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

        // 重用filters
        System.out.println("年龄大于 24岁的女性 Java programmers:");
        javaProgrammers.stream()
                .filter(ageFilter)
                .filter(genderFilter)
                .forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));
        System.out.println("最前面的3个 Java programmers:");
        javaProgrammers.stream()
                .limit(3)
                .forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

        System.out.println("最前面的3个女性 Java programmers:");
        javaProgrammers.stream()
                .filter(genderFilter)
                .limit(3)
                .forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

        System.out.println("工资最低的 Java programmer:");
        Person pers = javaProgrammers
                .stream()
                .min((p1, p2) -> (p1.getSalary() - p2.getSalary()))
                .get();

        System.out.printf("Name: %s %s; Salary: $%,d.", pers.getFirstName(), pers.getLastName(), pers.getSalary());

        System.out.println("工资最高的 Java programmer:");
        Person person = javaProgrammers
                .stream()
                .max((p, p2) -> (p.getSalary() - p2.getSalary()))
                .get();

        System.out.printf("Name: %s %s; Salary: $%,d.", person.getFirstName(), person.getLastName(), person.getSalary());

        System.out.println("根据 name 排序,并显示前5个 Java programmers:");
        List<Person> sortedJavaProgrammers = javaProgrammers
                .stream()
                .sorted((p, p2) -> (p.getFirstName().compareTo(p2.getFirstName())))
                .limit(5)
                .collect(Collectors.toList());

        sortedJavaProgrammers.forEach((p) -> System.out.printf("%s %s; %n", p.getFirstName(), p.getLastName()));

        System.out.println("根据 salary 排序 Java programmers:");
        sortedJavaProgrammers = javaProgrammers
                .stream()
                .sorted((p, p2) -> (p.getSalary() - p2.getSalary()))
                .collect(Collectors.toList());
        sortedJavaProgrammers.forEach((p) -> System.out.printf("%s %s; %n", p.getFirstName(), p.getLastName()));

        System.out.print("将 PHP programmers 的 first name 拼接成字符串:");
        String phpDevelopers = phpProgrammers
                .stream()
                .map(Person::getFirstName)
                .collect(Collectors.joining(" ; ")); // 在进一步的操作中可以作为标记(token)
        System.out.println(phpDevelopers);

        System.out.println("将 Java programmers 的 first name 存放到 Set:");
        Set<String> javaDevFirstName = javaProgrammers
                .stream()
                .map(Person::getFirstName)
                .collect(Collectors.toSet());

        System.out.println("将 Java programmers 的 first name 存放到 TreeSet:");
        TreeSet<String> javaDevLastName = javaProgrammers
                .stream()
                .map(Person::getLastName)
                .collect(Collectors.toCollection(TreeSet::new));

        //计算 count, min, max, sum, and average for numbers
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
        IntSummaryStatistics stats = numbers
                .stream()
                .mapToInt((x) -> x)
                .summaryStatistics();

        System.out.println("List中最大的数字 : " + stats.getMax());
        System.out.println("List中最小的数字 : " + stats.getMin());
        System.out.println("所有数字的总和   : " + stats.getSum());
        System.out.println("所有数字的平均值 : " + stats.getAverage());
    }
}