利用jdk8新特性对代码的优化

墨蓝 2023-07-22 03:43 10阅读 0赞

public class MyTest {
        //情景：实现list中的元素的过滤,求出集合中age>=30和salary>=300的元素
        List<TestUser> userList = Arrays.asList(
                new TestUser("张三",200.1,20),
                new TestUser("李四",300.2,25),
                new TestUser("王五",400.2,30),
                new TestUser("赵六",500.2,35)
        );
        //传统方法
        @Test
        public void test1(){
            List<TestUser> list = filterUser1(userList);
            for(TestUser user:list){
                System.out.println(user);
            }
            System.out.println("========================");
            List<TestUser> list2 = filterUser2(userList);
            for(TestUser user:list2){
                System.out.println(user);
            }
        }
    
        public List<TestUser> filterUser1(List<TestUser> userList) {
            List<TestUser> list = new ArrayList<>();
            for (TestUser user : userList) {
                if (user.getAge() >= 30) {
                    list.add(user);
                }
            }
            return list;
        }
        public List<TestUser> filterUser2(List<TestUser> userList) {
            List<TestUser>list = new ArrayList<>();
            for (TestUser user : userList) {
                if(user.getSalary()>=300){
                    list.add(user);
                }
            }
           return list;
        }

//定义一个接口和2个实现类
    public interface UserInterfase<T> {
        public boolean test(T t);
    }
    
    public class UserByAgeimpl implements UserInterfase<TestUser> {
        @Override
        public boolean test(TestUser user) {
            return user.getAge()>=30;
        }
    }
    
    public class UserBySalaryimpl implements UserInterfase<TestUser>{
        @Override
        public boolean test(TestUser user) {
            return user.getSalary()>300;
        }
    }

//优化方式一  策略设计模式
        @Test
        public void Test2(){
            List<TestUser> list = filterUser(userList, new UserByAgeimpl());
            for(TestUser user:list){
                System.out.println(user);
            }
            System.out.println("========================");
            List<TestUser> list2 = filterUser(userList, new UserBySalaryimpl());
            for(TestUser user:list2){
                System.out.println(user);
            }
        }
        public List<TestUser> filterUser(List<TestUser> userList,UserInterfase<TestUser>mp){
            List<TestUser>list = new ArrayList<>();
            for(TestUser user:userList){
               if(mp.test(user)){
                   list.add(user);
               }
            }
            return list;
        }
    
        //优化方式二  匿名内部类
        @Test
        public void test3(){
           List<TestUser>list = filterUser(userList, new UserInterfase<TestUser>() {
                @Override
                public boolean test(TestUser user) {
                    return user.getAge()>=30;
                }
            });
           for(TestUser user:list){
               System.out.println(user);
           }
            System.out.println("====================");
            List<TestUser>list2 = filterUser(userList, new UserInterfase<TestUser>() {
                @Override
                public boolean test(TestUser user) {
                    return user.getSalary()>=300;
                }
            });
            for(TestUser user:list2){
                System.out.println(user);
            }
        }
    
        //优化方式三  Lambda表达式
        @Test
        public void test4(){
            List<TestUser> list1 = filterUser(userList, (e) -> e.getAge() >= 30);
            List<TestUser> list2 = filterUser(userList, (e) -> e.getSalary() >= 300);
            list1.forEach(System.out::println);
            System.out.println("============================");
            list2.forEach(System.out::println);
        }
    
        //优化方式四   stream api
        @Test
        public void test5(){
            Stream<TestUser> list = userList.stream()
                    .filter((e) -> e.getAge() >= 30);
    
            list.forEach(System.out::println);
            System.out.println("========================");
            Stream<TestUser> list2 = userList.stream()
                    .filter((e) -> e.getSalary() >= 300);
            list2.forEach(System.out::println);
            System.out.println("========================");
            //取出list中的前2个
            Stream<TestUser> list3 = userList.stream()
                    .filter((e) -> e.getSalary() >= 300)
                    .limit(2);
            list3.forEach(System.out::println);
            System.out.println("========================");
            Stream<String> list4 = userList.stream()
                    .map(TestUser::getName);
            list4.forEach(System.out::println);
        }