Lambda基础用法

布满荆棘的人生 2022-04-02 05:37 331阅读 0赞

仅供初窥Lambda，示例demo，后续继续完善

package com.ohaotian.feifz.demo.lambdas;
    
    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.IntSummaryStatistics;
    import java.util.List;
    import java.util.Set;
    import java.util.TreeSet;
    import java.util.function.Consumer;
    import java.util.function.Predicate;
    
    import static java.util.stream.Collectors.joining;
    import static java.util.stream.Collectors.toCollection;
    import static java.util.stream.Collectors.toList;
    import static java.util.stream.Collectors.toSet;
    
    
    /**
     * @author feifz
     * @version 1.0.0
     * @Description Lambda基本用法
     * @origin https://www.cnblogs.com/franson-2016/p/5593080.html
     * @Date 2018/12/24 16:49
     */
    public class LambdaStreamDemo {
    
        public static void main(String[] args) {
            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));
                }
            };
    
            /**
             * 1.现在我们使用forEach方法来迭代输出上述列表:
             */
            System.out.println("forEach方法来迭代输出上述列表-->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()));
            /**
             * 使2.用forEach方法,增加程序员的工资5%:
             */
            System.out.println("使用forEach方法,增加程序员的工资5%-->");
            javaProgrammers.forEach((p) -> System.out.printf(" %s; ", p.getSalary()));
            phpProgrammers.forEach((p) -> System.out.printf(" %s; ", p.getSalary()));
            System.out.println("\n");
            Consumer<Person> giveRaise = e -> e.setSalary(e.getSalary() / 100 * 5 + e.getSalary());
            javaProgrammers.forEach(giveRaise);
            phpProgrammers.forEach(giveRaise);
            System.out.println("java程序员-->\n");
            javaProgrammers.forEach((p) -> System.out.printf(" %s; ", p.getSalary()));
            System.out.println("\nphp程序员-->\n");
            phpProgrammers.forEach((p) -> System.out.printf(" %s; ", p.getSalary()));
    
            /**
             * 3.过滤器filter() ,让我们显示月薪超过1400美元的PHP程序员:
             */
            System.out.println("\n下面是月薪超过 $1,400 的PHP程序员-->\n");
            phpProgrammers.stream()
                    .filter((p) -> (p.getSalary() > 1400))
                    .forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));
    
            /**
             * 4.定义过滤器,然后重用它们来执行其他操作
             */
            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("\n下面是年龄大于 24岁且月薪在$1,400以上的女PHP程序员-->\n");
            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("\n年龄大于 24岁的女性 Java programmers:\n");
            javaProgrammers.stream()
                    .filter(ageFilter)
                    .filter(genderFilter)
                    .forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));
    
            /**
             * 5.使用limit方法,可以限制结果集的个数:
             */
            System.out.println("\n最前面的3个 Java programmers:\n");
            javaProgrammers.stream()
                    .limit(3)
                    .forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));
    
    //风雨十年，同舟百年，我们在西安祝北京公司十周年生日快乐，创新不止，再创辉煌。
            System.out.println("\n最前面的3个女性 Java programmers:\n");
            javaProgrammers.stream()
                    .filter(genderFilter)
                    .limit(3)
                    .forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));
    
            /**
             * 6.排序呢? 我们在stream中能处理吗? 答案是肯定的。 在下面的例子中,我们将根据名字和薪水排序Java程序员,放到一个list中,然后显示列表:
             */
            System.out.println("\n根据 name 排序,并显示前5个 Java programmers:\n");
            List<Person> sortedJavaProgrammers = javaProgrammers
                    .stream()
                    .sorted((p, p2) -> (p.getFirstName().compareTo(p2.getFirstName())))
                    .limit(5)
                    .collect(toList());
    
            sortedJavaProgrammers.forEach((p) -> System.out.printf("%s %s; %n", p.getFirstName(), p.getLastName()));
    
            System.out.println("\n根据 salary 排序 Java programmers:\n");
            sortedJavaProgrammers = javaProgrammers
                    .stream()
                    .sorted( (p, p2) -> (p.getSalary() - p2.getSalary()) )
                    .collect( toList() );
    
            sortedJavaProgrammers.forEach((p) -> System.out.printf("%s %s; %n", p.getFirstName(), p.getLastName()));
    
            /**
             * 7.如果我们只对最低和最高的薪水感兴趣,比排序后选择第一个/最后一个 更快的是min和max方法:
             */
            System.out.println("\n工资最低的 Java programmer:\n");
            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("\n工资最高的 Java programmer:\n");
            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());
    
            /**
             * 8.结合 map 方法,我们可以使用 collect 方法来将我们的结果集放到一个字符串,一个 Set 或一个TreeSet中:
             */
            System.out.println("\n将 PHP programmers 的 first name 拼接成字符串:\n");
            String phpDevelopers = phpProgrammers
                    .stream()
                    .map(Person::getFirstName)
                    /**
                     * // 在进一步的操作中可以作为标记(token)
                     */
                    .collect(joining(" ; "));
    
            System.out.println("\n将 Java programmers 的 first name 存放到 Set:\n");
            Set<String> javaDevFirstName = javaProgrammers
                    .stream()
                    .map(Person::getFirstName)
                    .collect(toSet());
    
            System.out.println("将 Java programmers 的 first name 存放到 TreeSet:");
            TreeSet<String> javaDevLastName = javaProgrammers
                    .stream()
                    .map(Person::getLastName)
                    .collect(toCollection(TreeSet::new));
    
            /**
             * 9.Streams 还可以是并行的(parallel)。 示例如下:
             */
            System.out.println("计算付给 Java programmers 的所有money:");
            int totalSalary = javaProgrammers
                    .parallelStream()
                    .mapToInt(p -> p.getSalary())
                    .sum();
            System.out.println(totalSalary);
    
            /**
             * 10.我们可以使用summaryStatistics方法获得stream 中元素的各种汇总数据。 接下来,我们可以访问这些方法,比如getMax, getMin, getSum或getAverage:
             */
            //计算 count, min, max, sum, and average for numbers
            List<Integer> numbers = Arrays.asList(1, 21, 3, 44, 5, 6, 77, 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());
        }
    
    
    }