Lambda表达式的优势

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 comparator = new Comparator() {

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

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

//Lambda表达式
    @Test
    public void test2(){
        Comparator comparator = (x ,y) -> Integer.compare(x, y);
        TreeSet 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 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 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 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 filterEmployee(List employeeList){
      List 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 filterEmployees2(List employeeList){
  
      ArrayList 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 {
  
  public boolean test(T t);
  }

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

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

  @Test
  public void test4(){
      List 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 employeeList1 = filterEmployee(this.employees, new FilterEmployeeBySalary());
  
      for (Employee employee : employeeList1){
          System.out.println(employee);
      }
  
  }
  public List filterEmployee(List employeeList, MyPredicate mp){
      ArrayList 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 {
  
  public boolean test(T t);
  }

  @Test
  public void test5(){
      List employeeList = filterEmployee(employees, new MyPredicate() {
          @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 employeeList1 = filterEmployee(employees, new MyPredicate() {
          @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 filterEmployee(List employeeList, MyPredicate mp){
      ArrayList 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 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 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);
  }