How to find Max Date in List Object

Question

Consider a class User  public class User    int userId    String name    Date date      Now I have a List lt User gt  of size 20  how can I find the max date in the list without using manual iterator

User · Accepted Answer

Since you are asking for lambdas  you can use the following syntax with Java 8   Date maxDate   list stream   map u - gt  u date  max Date  compareTo  get      or  if you have a getter for the date   Date maxDate   list stream   map User  getDate  max Date  compareTo  get

User · Answer

Comparator lt User gt  cmp   new Comparator lt User gt           Override     public int compare User user1  User user2            return user1 date compareTo user2 date             Collections max list  cmp

User · Answer

self-explanatory style import static java util Comparator naturalOrder           list stream            map User  getDate           max naturalOrder             orElse null              replace with  orElseThrow   is the list cannot be empty

User · Answer

A small improvement from the accepted answer is to do the null check and also get full object   public class DateComparator    public static void main String   args  throws ParseException       SimpleDateFormat format   new SimpleDateFormat  yyyy-MM-dd         List lt Employee gt  employees   new ArrayList lt  gt         employees add new Employee 1   name1   addDays new Date    1         employees add new Employee 2   name2   addDays new Date    3         employees add new Employee 3   name3   addDays new Date    6         employees add new Employee 4   name4   null        employees add new Employee 5   name5   addDays new Date    4         employees add new Employee 6   name6   addDays new Date    5         System out println employees       Date maxDate   employees stream   filter emp - gt  emp getJoiningDate      null  map Employee  getJoiningDate  max Date  compareTo  get        System out println format format maxDate          Comparator lt Employee gt  comparator    p1  p2  - gt  p1 getJoiningDate   compareTo p2 getJoiningDate         Comparator lt Employee gt  comparator   Comparator comparing Employee  getJoiningDate       Employee maxDatedEmploye   employees stream   filter emp - gt  emp getJoiningDate      null  max comparator  get        System out println   maxDatedEmploye       maxDatedEmploye        Employee minDatedEmployee   employees stream   filter emp - gt  emp getJoiningDate      null  min comparator  get        System out println   minDatedEmployee       minDatedEmployee       public static Date addDays Date date  int days        Calendar cal   Calendar getInstance        cal setTime date       cal add Calendar DATE  days      minus number would decrement the days     return cal getTime          You would get below results      Employee  empId 1  empName name1  joiningDate Wed Mar 21 13 33 09 EDT 2018   Employee  empId 2  empName name2  joiningDate Fri Mar 23 13 33 09 EDT 2018   Employee  empId 3  empName name3  joiningDate Mon Mar 26 13 33 09 EDT 2018   Employee  empId 4  empName name4  joiningDate null   Employee  empId 5  empName name5  joiningDate Sat Mar 24 13 33 09 EDT 2018   Employee  empId 6  empName name6  joiningDate Sun Mar 25 13 33 09 EDT 2018    2018-03-26  maxDatedEmploye   Employee  empId 3  empName name3  joiningDate Mon Mar 26 13 33 09 EDT 2018    minDatedEmployee   Employee  empId 1  empName name1  joiningDate Wed Mar 21 13 33 09 EDT 2018    Update   What if list itself is empty            Date maxDate   employees stream   filter emp - gt  emp getJoiningDate      null  map Employee  getJoiningDate  max Date  compareTo  orElse new Date         System out println format format maxDate        Comparator lt Employee gt  comparator   Comparator comparing Employee  getJoiningDate       Employee maxDatedEmploye   employees stream   filter emp - gt  emp getJoiningDate      null  max comparator  orElse null       System out println   maxDatedEmploye       maxDatedEmploye

User · Answer

LocalDate maxDate   dates stream                                max  Comparator comparing  LocalDate  toEpochDay                                  get     LocalDate minDate   dates stream                                min  Comparator comparing  LocalDate  toEpochDay                                  get

User · Answer

Just use Kotlin   val list   listOf user1  user2  user3  val maxDate   list maxBy   it date    date

User · Answer

troubleshooting-friendly style You should not call  get   directly  Optional lt  gt   that Stream  max returns  was designed to benefit from  orElse    inline handling   If you are sure your arguments have their size of 2    list stream        map u - gt  u date       max Date  compareTo       orElseThrow    - gt  new IllegalArgumentException  quot Expected  list  to be of size   gt   2  Was  0 quot       If you support empty lists  then return some default value  for example   list stream        map u - gt  u date       max Date  compareTo       orElse new Date Long MIN VALUE     CREDITS to   JimmyGeers   assylias from the accepted answer

[java] How to find Max Date in List<Object>?

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