Java8 Lambda表达式和Stream API示例 （像Scala了）

Lambda是一个匿名函数，可以将Lambda表达式理解为是一段可以传递代码。

package com.expgiga.Java8;/** * */public class Employee {    private String name;    private int age;    private double salary;    public Employee() {    }    public Employee(String name, int age, double salary) {        this.name = name;        this.age = age;        this.salary = salary;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public double getSalary() {        return salary;    }    public void setSalary(double salary) {        this.salary = salary;    }    @Override    public String toString() {        return "Employee{" +                "name='" + name + '\'' +                ", age=" + age +                ", salary=" + salary +                '}';    }}

package com.expgiga.Java8;/** * */public interface MyPredicate<T> {    public boolean test(T t);}

package com.expgiga.Java8;/** * */public class FilterEmployeeByAge implements MyPredicate<Employee> {    @Override    public boolean test(Employee employee) {        return employee.getAge() > 16;    }}

package com.expgiga.Java8;/** * */public class FilterEmployeeBySalary implements MyPredicate<Employee> {    @Override    public boolean test(Employee employee) {        return employee.getSalary() > 19999;    }}

package com.expgiga.Java8;import java.util.*;/** * */public class TestLambda {    public static void main(String[] args) {        //原来的匿名内部类        Comparator<Integer> com = new Comparator<Integer>() {            @Override            public int compare(Integer o1, Integer o2) {                return Integer.compare(o1, o2);            }        };        TreeSet<Integer> ts = new TreeSet<>(com);        //lambda表达式        Comparator<Integer> comparator = (x, y) -> Integer.compare(x, y);        TreeSet<Integer> treeSet = new TreeSet<>(comparator);        //需求：获取当前公司中员工年龄大于16的员工信息        List<Employee> employeeList = Arrays.asList(                new Employee("zhangsan", 18, 19999),                new Employee("lisi", 28, 29999),                new Employee("wangwu", 38, 39999),                new Employee("zhaoliu", 16, 17999),                new Employee("tianqi", 6, 12999)        );        List<Employee> list = filterEmployees(employeeList);        for (Employee e : list) {            System.out.println(e);        }        //需求，获取当前公司中员工工资大于19999的员工的信息        List<Employee> list2 = filterEmployees2(employeeList);        for (Employee e : list2) {            System.out.println(e);        }        //优化代码一：策略设计模式        List<Employee> list3 = filterEmployee(employeeList, new FilterEmployeeByAge());        for (Employee e : list3) {            System.out.println(e);        }        List<Employee> list4 = filterEmployee(employeeList, new FilterEmployeeBySalary());        for (Employee e : list4) {            System.out.println(e);        }        //优化代码二：匿名内部类        List<Employee> list5 = filterEmployee(employeeList, new MyPredicate<Employee>() {            @Override            public boolean test(Employee employee) {                return employee.getSalary() < 19999;            }        });        for (Employee employee : list5) {            System.out.println(employee);        }        //优化代码三：Lambda表达式        List<Employee> list6 = filterEmployee(employeeList, (e) -> e.getSalary() < 19999);        for (Employee e : list6) {            System.out.println(e);        }        System.out.println("------------------------------");        //优化代码四：Stream API        employeeList.stream().filter((e) -> e.getSalary() < 19999).limit(1).forEach(System.out::println);        System.out.println("==============================");        employeeList.stream().map(Employee::getName).forEach(System.out::println);    }    public static List<Employee> filterEmployees(List<Employee> list) {        List<Employee> emps = new ArrayList<>();        for (Employee e : list) {            if (e.getAge() > 16) {                emps.add(e);            }        }        return emps;    }    public static List<Employee> filterEmployees2(List<Employee> list) {        List<Employee> emps = new ArrayList<>();        for (Employee e : list) {            if (e.getSalary() > 19999) {                emps.add(e);            }        }        return emps;    }    //优化代码一：策略设计模式    public static List<Employee> filterEmployee(List<Employee> list, MyPredicate<Employee> employeeMyPredicate) {        List<Employee> emps = new ArrayList<>();        for (Employee employee : list) {            if (employeeMyPredicate.test(employee)) {                emps.add(employee);            }        }        return emps;    }    //优化代码二：匿名内部类}