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


}