// 1. 不需要引數,返回值為 5  
() -> 5  
// 2. 接收一個引數(數字型別),返回其2倍的值  
x -> 2 * x  
// 3. 接受2個引數(數字),並返回他們的差值  
(x, y) -> x – y  
// 4. 接收2個int型整數,返回他們的和  
(int x, int y) -> x + y  
// 5. 接受一個 string 物件,並在控制檯列印,不返回任何值(看起來像是返回void)  
(String s) -> System.out.print(s) 
// 6. 方法體多條語句
 (String s) -> {System.out.print(s)；
                System.out.print(s+1)；
                }
 

用法1：

new Thread(() -> System.out.println("Hello world !")).start();

Runnable race2 = () -> System.out.println("Hello world !");     
race2.run(); 

用法2：

String[] atp = {"Rafael Nadal", "Novak Djokovic",  
       "Stanislas Wawrinka",  
       "David Ferrer","Roger Federer",  
       "Andy Murray","Tomas Berdych",  
       "Juan Martin Del Potro"};  
List<String> players =  Arrays.asList(atp);  
  
// 以前的迴圈方式  
for (String player : players) {  
     System.out.print(player + "; ");  
}  
  
// 使用 lambda 表示式以及函式操作(functional operation)  
players.forEach((player) -> System.out.print(player + "; "));  
   
// 在 Java 8 中使用雙冒號操作符(double colon operator)  
players.forEach(System.out::println);
 

用法3：使用Lambdas和Streams
Stream是對集合的包裝,通常和lambda一起使用。 使用lambdas可以支援許多操作,如 map, filter, limit, sorted, count, min, max, sum, collect 等等。 同樣,Stream使用懶運算,他們並不會真正地讀取所有資料,遇到像getFirst() 這樣的方法就會結束鏈式語法。 在接下來的例子中,我們將探索lambdas和streams 能做什麼。 我們建立了一個Person類並使用這個類來新增一些資料到list中,將用於進一步流操作。 Person 只是一個簡單的POJO類:

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;  
} 
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));  
  }  
};  

System.out.println("下面是月薪超過 $1,400 的PHP程式設計師:")  
javaProgrammers.stream()  
          .filter((p) -> (p.getSalary() > 1400))  
          .forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

// 定義 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("下面是年齡大於 24歲且月薪在$1,400以上的女PHP程式設計師:");  
javaProgrammers.stream()  
          .filter(ageFilter)  
          .filter(salaryFilter)  
          .filter(genderFilter)  
          .forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName())); 

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

System.out.println("根據 name 排序,並顯示前5個 Java programmers:");  
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("根據 salary 排序 Java programmers:");  
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()));

System.out.println("工資最低的 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("工資最高的 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())