Lambda表达式的优势

1. 匿名内部类和Lambda的对比

//原来的匿名内部类
    @Test
    public void test1(){
        Comparator<Integer> comparator = new Comparator<Integer>() {

            @Override
            public int compare(Integer o1, Integer o2) {
                return Integer.compare(o1, o2);
            }
        };

        TreeSet<Integer> ts = new TreeSet<>(comparator);
    }

//Lambda表达式
    @Test
    public void test2(){
        Comparator<Integer> comparator = (x ,y) -> Integer.compare(x, y);
        TreeSet<Integer> ts = new TreeSet<>(comparator);

    }

2. 用Lambda表达式优化代码

需求1：获取当前公司中员工年龄大于35的员工信息

需求2：获取当前公司中员工工资大于5000的员工信息

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public class Employee {
private String name;
private int age;
private double salary;

public Employee() {
    super();
}

public Employee(String name, int age, double salary) {
    super();
    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 +
            '}';
}
}

List<Employee> employees = Arrays.asList(
        new Employee("张三", 18 ,9999.99),
        new Employee("李四", 38, 5555.99),
        new Employee("王五", 50, 6666.66),
        new Employee("赵六", 16, 3333.33),
        new Employee("田七", 8, 7777.77)
);

实现方式

@Test
public void test3(){
            //获取年龄大于35岁的员工信息
    List<Employee> employeeList = filterEmployee(employees);
    System.out.println("年龄大于35岁的员工信息：");
    for (Employee employee : employeeList){
        System.out.println(employee);
    }

    //获取当前公司中员工工资大于5000的员工信息
    List<Employee> employeeList1 = filterEmployees2(employees);
    System.out.println("工资大于5000的员工信息：");
    for (Employee employee : employeeList1){
        System.out.println(employee);
    }
}

获取当前公司中员工年龄大于35的员工信息
public List<Employee> filterEmployee(List<Employee> employeeList){
    List<Employee> emps = new ArrayList<>();

    for (Employee emp : employeeList){
        if (emp.getAge() >= 35){
            emps.add(emp);
        }
    }
    return emps;
}

获取当前公司中员工工资大于5000的员工信息
public List<Employee> filterEmployees2(List<Employee> employeeList){

    ArrayList<Employee> employees = new ArrayList<>();
    for (Employee employee : employeeList){
        if (employee.getSalary() >= 5000){
            employees.add(employee);
        }
    }
    return employees;
}

优化方案一：策略设计模式

public interface MyPredicate<T> {

public boolean test(T t);
}

public class FilterEmployeeByAge implements MyPredicate<Employee>{
@Override
public boolean test(Employee employee) {
    return employee.getAge() >= 35;
}
}

public class FilterEmployeeBySalary implements MyPredicate<Employee>{
@Override
public boolean test(Employee employee) {
    return employee.getSalary() >= 5000;
}
}

@Test
public void test4(){
    List<Employee> employeeList = filterEmployee(employees, new FilterEmployeeByAge());
    System.out.println("年龄大于35岁的员工信息：");
    for (Employee employee : employeeList){
        System.out.println(employee);
    }

    System.out.println("工资大于5000的员工信息：");
    List<Employee> employeeList1 = filterEmployee(this.employees, new FilterEmployeeBySalary());

    for (Employee employee : employeeList1){
        System.out.println(employee);
    }

}
public List<Employee> filterEmployee(List<Employee> employeeList, MyPredicate<Employee> mp){
    ArrayList<Employee> employees = new ArrayList<>();

    for (Employee employee : employeeList){
        if (mp.test(employee)){
            employees.add(employee);
        }
    }
    return employees;
}

优化方案二：匿名内部类

public interface MyPredicate<T> {

public boolean test(T t);
}

@Test
public void test5(){
    List<Employee> employeeList = filterEmployee(employees, new MyPredicate<Employee>() {
        @Override
        public boolean test(Employee employee) {
            return employee.getAge() >= 35;
        }
    });
    System.out.println("年龄大于35岁的员工信息：");
    for (Employee employee : employeeList){
        System.out.println(employee);
    }

    List<Employee> employeeList1 = filterEmployee(employees, new MyPredicate<Employee>() {
        @Override
        public boolean test(Employee employee) {
            return employee.getSalary() >= 5000;
        }
    });
    System.out.println("工资大于5000的员工信息：");
    for (Employee employee : employeeList1){
        System.out.println(employee);
    }
}

优化方案三：Lambda表达式

public List<Employee> filterEmployee(List<Employee> employeeList, MyPredicate<Employee> mp){
    ArrayList<Employee> employees = new ArrayList<>();

    for (Employee employee : employeeList){
        if (mp.test(employee)){
            employees.add(employee);
        }
    }
    return employees;
}

@Test
public void test6(){
    System.out.println("年龄大于35岁的员工信息：");
    List<Employee> employeeList = filterEmployee(employees, (e) -> e.getAge() >= 35);
    employeeList.forEach(System.out::println);

    System.out.println("工资大于5000的员工信息：");
    List<Employee> employeeList1 = filterEmployee(employees, (e) -> e.getSalary() >= 5000);
    employeeList1.forEach(System.out::println);
}

优化方案四：Lambda表达式和Stream API

@Test
public void test7(){
    System.out.println("年龄大于35岁的员工信息：");
    employees.stream()
             .filter((e) -> e.getAge() >= 35)
             .forEach(System.out::println);

    System.out.println("工资大于5000的员工信息：");
    employees.stream()
             .filter((e) -> e.getSalary() >= 5000)
             .forEach(System.out::println);
}

本文标题：Lambda表达式的优势
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