java8 lambda表达式详解及示例

r囧r小猫 2023-06-06 12:09 79阅读 0赞

lambda表达式是java8的新特性，这里做简单的介绍和常用功能的示例

在使用lambda表达式时，较为重要的一个内容则是stream(在后面的示例中会经常用到stream，在这里先做介绍一下，有个概念和映象)

具体可以参考如下博客地址

[https://blog.csdn.net/lidai352710967/article/details/82496783][https_blog.csdn.net_lidai352710967_article_details_82496783]

下面是lambda表达式的示例代码：

package com.delta.lambdaTest;
    
    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.Collections;
    import java.util.Comparator;
    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 java.util.stream.Collectors;
    
    import com.mysql.cj.x.protobuf.MysqlxCrud.Collection;
    
    public class LambdaTest {
    	public static void main(String[] args) {
    		int num = Runtime.getRuntime().availableProcessors();
    		System.out.println("处理器："+num);
    		
    		
    		//不用时
    		new Thread(new Runnable() {
    			
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				System.out.println("不用lambda时实现方法");
    			}
    		}).start();
    		//Lambda表达式实现runnable
    		new Thread(()-> {
    			System.out.println("lambda实现run方法");
    		}).start();
    		
    		//用lambda表达式对列表进行迭代
    		
    		 String[] atp = {"Rafael Nadal", "Novak Djokovic",
    	                "Stanislas Wawrinka",
    	                "David Ferrer","Roger Federer",
    	                "Andy Murray","Tomas Berdych",
    	                "Juan Martin Del Potro"};
    		 
    		 //把当前的Array转换为List
    		 List<String> players = Arrays.asList(atp);
    		 //以前使用循环
    		 for(String player: players) {
    			 System.out.println(player+" ,");
    		 }
    		 
    		 //使用lambda表达式
    		 System.out.println("使用lambda实现for");
    		 players.forEach((player)->System.out.println(player+"' "));
    		 
    		 //zai java8中使用双：实现迭代 forEach仅仅是做迭代用，没有任何返回值 需要处理的函数在()括号中传入
    		 System.out.println("java8 中使用双：");
    		 players.forEach(System.out::println);
    		 players.forEach((player)->{
    			String playerTemp = player+"-"+"test"+" ";
    			System.out.println("playerTemp is:"+playerTemp);
    		 });
    		 
    		 //使用lambda表达式做集合排序
    		 System.out.println("排序---匿名内部内");
    //		 players.sort(new Comparator<String>() {
    //
    //			@Override
    //			public int compare(String o1, String o2) {
    //				// TODO Auto-generated method stub
    //				return o1.compareTo(o2);
    //			}
    //		});
    		 
    		 players.forEach((player)->System.out.println(player));
    		 //先定义排序的方法
    		 Comparator<String> sortByName = (String s1,String s2)->(s1.compareTo (s2));
    		 //先进行排序
    		 Collections.sort(players,sortByName);
    		 System.out.println("排序后");
    		 players.forEach((player)->System.out.println(player));
    		 
    		 //使用lambda表达式和函数式接口Predicate
    		 System.out.println("测试Predicate");
    		 testPredicate();
    		 
    		 
    		 
    		 
    	}
    	
    	public static void testPredicate() {
    		
    		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java程序员的姓名");
            javaProgrammers.forEach((p)->System.out.printf("%s %s;",p.getFirstName(),p.getLastName()));
            System.out.println("所有php程序员的姓名");
            phpProgrammers.forEach((p)->System.out.printf("%s %s;",p.getFirstName(),p.getLastName()));
            
            //Consumer是java8的函数式接口
            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.getSalary()));
            
            //自定义filter
            //先自己定义好filter的内容 做为过滤用，下面直接用名称即可
            Predicate<Person> ageFilter = (p)->(p.getAge()>25);
            Predicate<Person> salaryFilter = (p)->(p.getSalary()>1400);
            Predicate<Person> genderFilter = (p)->(p.getGender().equals("female"));
            
            Consumer<Person> pConsumer = p->System.out.printf("%s %s; ",p.getFirstName(),p.getLastName());
            
            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(pConsumer);
            
            // 重用filters consumers
            System.out.println("年龄大于 24岁的女性 Java programmers:");
            javaProgrammers.stream().filter(ageFilter).filter(salaryFilter).filter(genderFilter)
                                    .forEach(pConsumer);
            
            
            System.out.println("最前面的3个 Java programmers:");
            javaProgrammers.stream().limit(3).forEach(pConsumer);
            System.out.println("最前面的3个女性 Java programmers:");
            
            javaProgrammers.stream().filter(genderFilter).limit(3).forEach(pConsumer);
            
            //排序
            
            System.out.println("根据 name 排序,并显示前5个 Java programmers:");
            Comparator<Person> pNameCompare = (p1,p2)->(p1.getFirstName().compareTo(p2.getFirstName()));
            Comparator<Person> pSalartComparator = (p1,p2)->(p1.getSalary()-p2.getSalary());
            
            List<Person> sortedJavaProgramers = javaProgrammers
            		                            .stream()
            		                            .sorted(pNameCompare)
            		                            .limit(5)
            		                            .collect(Collectors.toList());
            sortedJavaProgramers.forEach(pConsumer);
            
            System.out.println("根据 salary 排序 Java programmers:");
            
            sortedJavaProgramers.stream().sorted(pSalartComparator).collect(Collectors.toList());
            
            sortedJavaProgramers.forEach(pConsumer);
            
            
            //min和max方法
            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 perMax = javaProgrammers.stream().max((p1,p2)->(p1.getSalary()-p2.getSalary())).get();
            
            System.out.printf("Name: %s %s; Salary: $%,d.", perMax.getFirstName(), perMax.getLastName(), perMax.getSalary());
            
            
            
            System.out.println("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:  "+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());
            javaDevFirstName.forEach(fp->System.out.printf("%s; ",fp));
            
            System.out.println("将 Java programmers 的 first name 存放到 TreeSet:");
            
            TreeSet<String> javaDevLasName = javaProgrammers.stream().map(Person::getLastName).collect(Collectors.toCollection(TreeSet::new));
            javaDevLasName.forEach(fp->System.out.printf("%s; ",fp));
            
            
            //Streams 还可以是并行的(parallel). Stream是对集合的包装
            System.out.println("计算付给 Java programmers 的所有money:");
            int totalSlary = javaProgrammers.parallelStream().mapToInt(p->p.getSalary()).sum();
            System.out.println("totalSalary is:"+totalSlary);
            
          //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(1,2,3,4,5,6,7,8,9,10);
            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());
            
            
            
            
            
    
    	}
    
    }
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    package com.delta.lambdaTest;
    
    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;
        }
    
    }

[https_blog.csdn.net_lidai352710967_article_details_82496783]: https://blog.csdn.net/lidai352710967/article/details/82496783