Java8部分特性及list的常见操作

1. Java8部分特性及list的常见操作

public class SkuList {
    public static void main(String[] args) {
 
        List<User> students = new ArrayList<>();
        User st1 = new User();
        st1.setId(123);
        st1.setAge(10);
 
        User st2 = new User();
        st2.setId(789);
        st2.setAge(20);
 
        User st3 = new User();
        st3.setId(456);
        st3.setAge(20);
        students.add(st1);
        students.add(st2);
        students.add(st3);
 
        /*  TODO: 输出：list分割：[[{"age":10,"id":123},{"age":20,"id":123}],[{"age":20,"id":456}]]
        List<List<User>> splits = Lists.partition(students, 2);
        System.out.println("list分割：" + JSON.toJSONString(splits));*/
 
        /*  TODO: 输出：list根据年龄进行分组：{20:[{"age":20,"id":123},{"age":20,"id":456}],10:[{"age":10,"id":123}]}
        Map<Integer, List<User>> listMap = students.stream().collect(Collectors.groupingBy(User::getAge));
        System.out.println("list根据年龄进行分组：" + JSON.toJSONString(listMap));*/
 
        /*  TODO: 输出：list转换为Map：{789:{"age":20,"id":789},456:{"age":20,"id":456},123:{"age":10,"id":123}}
        Map<Integer, User> userMap = students.stream().collect(Collectors.toMap(User::getId, Function.identity()));
        System.out.println("list转换为Map：" + JSON.toJSONString(userMap));*/
 
        /*  TODO: 输出：list过滤filter :[{"age":20,"id":789},{"age":20,"id":456}]
        List<User> oldStu = students.stream().filter(
                student -> student.getAge() > 10).collect(Collectors.toList());
        System.out.println("list过滤filter :" + JSON.toJSONString(oldStu));*/
 
        /*  TODO: 输出：list对象转化:[{"age":10,"id":123,"title":"教师"},{"age":20,"id":789,"title":"教师"},{"age":20,"id":456,"title":"教师"}]
        List<Teacher> teachers = students.stream().map(
                student -> {
                    Teacher teacher = new Teacher();
                    BeanUtils.copyProperties(student, teacher);
                    teacher.setTitle("教师");
                    return teacher;
                }).collect(Collectors.toList());
        System.out.println("list对象转化:" + JSON.toJSONString(teachers));*/
 
        /*  TODO: 输出：list转set：[20, 10]
        Set<Integer> ages = students.stream().map(User::getAge).collect(Collectors.toSet());
        System.out.println("list转set：" + ages);*/
 
        /*  TODO: 输出：[奔驰, 宝马, 奥迪]
        List<Customer> customerList = new ArrayList<>();
        customerList.add(new Customer(1L, "奔驰"));
        customerList.add(new Customer(2L, "宝马"));
        customerList.add(new Customer(3L, null));
        customerList.add(null);
        customerList.add(new Customer(5L, null));
        customerList.add(new Customer(6L, "奥迪"));
 
 
        List<String> nameList1 = customerList.stream()
                .filter(Objects::nonNull) // 過濾掉Customer為null的元素
                .map(Customer::getName)
                .filter(Objects::nonNull) // 過濾掉Customer.getName()為null的元素
                .collect(Collectors.toList());
        
        System.out.println(nameList1);*/
    }
}
 
@Data
class User {
    private Integer id;
    private Integer age;
 
}
 
/**
 * 转换使用
 */
@Data
class Teacher {
    private Integer id;
    private Integer age;
    private String title;
}
 
@Data
@AllArgsConstructor
class Customer {
    private Long id;
    private String name;
 
}