Sort objects by field java

Java 8 – Sorting list of objects on multiple fields

In one of the previous article, we discussed on how to sort list of objects on multiple field/parameters where we have coded/developed our own customized Comparator.

We will reuse the same example to sort on multiple fields using Java 8 Comparator in a more elegant way using different approaches.

1. Comparator interface :

• This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference
• A comparison function, which imposes a total ordering on some collection of objects
• Comparators can be passed to a sort method (such as Collections.sort or Arrays.sort ) to allow precise control over the sort order

2. Multiple Sorting using Comparator :

• Using Java 8 Comparator, we are going to sort list of Customer objects on the basis of three attributes viz.; name, city and their age
• First, we are going to sort the list according to their name
• Second, if name of the 2/3 customers are same then we are going to sort on the basis of their city
• Third and finally, if customers name/city are same then we are going to sort on the basis of their age in ascending order
• We can achieve this target using different approaches namely,
  1. using Lambda Expression
  2. using Method Reference
  3. Inline sorting using Comparator
  4. Collection.sort() method
  5. Arrays.sort() method
• All the above mentioned approaches produces same result but the way they are implemented using Java 8 Comparator differs

Customer.java

package net.bench.resources.stream.sorting.multiple.fields; public class Customer < // member variables String custName; String custCity; Integer custAge; // 3-arg parameterized constructor // getters & setters // toString() method >

2.1 using Lambda Expression :

• In this approach, we are going to define 3 different Comparators using Lambda Expression as shown below
  • 1 st Name Comparator :- (cust1, cust2) -> cust1.getCustName().compareTo(cust2.getCustName())
  • 2 nd City Comparator :- (cust1, cust2) -> cust1.getCustCity().compareTo(cust2.getCustCity())
  • 3 rd Age Comparator :- (cust1, cust2) -> cust1.getCustAge().compareTo(cust2.getCustAge())

  MultipleSortingUsingJava8Lambda.java

  package net.bench.resources.stream.sorting.multiple.fields; import java.util.Arrays; import java.util.Comparator; import java.util.List; import java.util.stream.Collectors; public class MultipleSortingUsingJava8Lambda < // customer list private static ListgetUnSortedCustomers() < return Arrays.asList( new Customer("Shalini", "Chennai", 60), new Customer("Sneha", "Pune", 73), new Customer("Simran", "Bangalore", 37), new Customer("Trisha", "Hyderabad", 52), new Customer("Shalini", "Chennai", 70), new Customer("Abirami", "Bangalore", 48), new Customer("Trisha", "Mangalore", 45), new Customer("Sneha", "Pune", 62), new Customer("Shalini", "Chennai", 50) ); >// main() method public static void main(String[] args) < // get customer list ListunsortedCustomerList = getUnSortedCustomers(); System.out.println("Before Sorting: Customer list :- \n"); unsortedCustomerList.stream().forEach(System.out::println); System.out.println("\n\nSorted Customer list on multiple fields" + " using Lambda Expression :- \n"); // 1. customer Name comparator Comparator nameComparatorLEx = (cust1, cust2) -> cust1.getCustName().compareTo(cust2.getCustName()); // 2. customer City comparator Comparator cityComparatorLEx = (cust1, cust2) -> cust1.getCustCity().compareTo(cust2.getCustCity()); // 3. customer Age comparator Comparator ageComparatorLEx = (cust1, cust2) -> cust1.getCustAge().compareTo(cust2.getCustAge()); // sorting on multiple fields (3-level) using Lambda expression List sortedCustomerList = unsortedCustomerList .stream() .sorted( nameComparatorLEx // 1st compare Name .thenComparing(cityComparatorLEx) // then 2nd compare City .thenComparing(ageComparatorLEx)) // then 3rd compare Age .collect(Collectors.toList()); // collect sorted customers to new list // print new list to console using forEach() sortedCustomerList.stream().forEach(cust -> System.out.println(cust)); > >

  Output:

  Before Sorting: Customer list :- Customer [custName=Shalini, custCity=Chennai, custAge=60] Customer [custName=Sneha, custCity=Pune, custAge=73] Customer [custName=Simran, custCity=Bangalore, custAge=37] Customer [custName=Trisha, custCity=Hyderabad, custAge=52] Customer [custName=Shalini, custCity=Chennai, custAge=70] Customer [custName=Abirami, custCity=Bangalore, custAge=48] Customer [custName=Trisha, custCity=Mangalore, custAge=45] Customer [custName=Sneha, custCity=Pune, custAge=62] Customer [custName=Shalini, custCity=Chennai, custAge=50] Sorted Customer list on multiple fields using Lambda Expression :- Customer [custName=Abirami, custCity=Bangalore, custAge=48] Customer [custName=Shalini, custCity=Chennai, custAge=50] Customer [custName=Shalini, custCity=Chennai, custAge=60] Customer [custName=Shalini, custCity=Chennai, custAge=70] Customer [custName=Simran, custCity=Bangalore, custAge=37] Customer [custName=Sneha, custCity=Pune, custAge=62] Customer [custName=Sneha, custCity=Pune, custAge=73] Customer [custName=Trisha, custCity=Hyderabad, custAge=52] Customer [custName=Trisha, custCity=Mangalore, custAge=45]

  2.2 using Method reference :

  • In this approach, we are going to define 3 different Comparators using Method Reference as shown below
    • 1 st Name Comparator :- Comparator.comparing(Customer::getCustName)
    • 2 nd City Comparator :- Comparator.comparing(Customer::getCustCity)
    • 3 rd Age Comparator :- Comparator.comparing(Customer::getCustAge)

    MultipleSortingUsingJava8MethodReference.java

    package net.bench.resources.stream.sorting.multiple.fields; import java.util.Arrays; import java.util.Comparator; import java.util.List; import java.util.stream.Collectors; public class MultipleSortingUsingJava8MethodReference < // customer list private static ListgetUnSortedCustomers() < return Arrays.asList( new Customer("Shalini", "Chennai", 60), new Customer("Sneha", "Pune", 73), new Customer("Simran", "Bangalore", 37), new Customer("Trisha", "Hyderabad", 52), new Customer("Shalini", "Chennai", 70), new Customer("Abirami", "Bangalore", 48), new Customer("Trisha", "Mangalore", 45), new Customer("Sneha", "Pune", 62), new Customer("Shalini", "Chennai", 50) ); >public static void main(String[] args) < // get customer list ListunsortedCustomerList = getUnSortedCustomers(); System.out.println("Before Sorting: Customer list :- \n"); unsortedCustomerList.stream().forEach(System.out::println); System.out.println("\n\nSorted Customer list on multiple fields" + " using Method Reference :- \n"); // 1. customer Name comparator Comparator nameComparatorMRef = Comparator .comparing(Customer::getCustName); // 2. customer City comparator Comparator cityComparatorMRef = Comparator .comparing(Customer::getCustCity); // 3. customer Age comparator Comparator ageComparatorMRef = Comparator .comparing(Customer::getCustAge); // sorting on multiple fields (3-level) using Method Reference List sortedCustomerList = unsortedCustomerList .stream() .sorted( nameComparatorMRef // 1st compare Name .thenComparing(cityComparatorMRef) // then 2nd compare City .thenComparing(ageComparatorMRef)) // then 3rd compare Age .collect(Collectors.toList()); // collect sorted customers to new list // print new list to console using forEach() sortedCustomerList.stream().forEach(System.out::println); > >

    Output:

    Before Sorting: Customer list :- Customer [custName=Shalini, custCity=Chennai, custAge=60] Customer [custName=Sneha, custCity=Pune, custAge=73] Customer [custName=Simran, custCity=Bangalore, custAge=37] Customer [custName=Trisha, custCity=Hyderabad, custAge=52] Customer [custName=Shalini, custCity=Chennai, custAge=70] Customer [custName=Abirami, custCity=Bangalore, custAge=48] Customer [custName=Trisha, custCity=Mangalore, custAge=45] Customer [custName=Sneha, custCity=Pune, custAge=62] Customer [custName=Shalini, custCity=Chennai, custAge=50] Sorted Customer list on multiple fields using Method Reference :- Customer [custName=Abirami, custCity=Bangalore, custAge=48] Customer [custName=Shalini, custCity=Chennai, custAge=50] Customer [custName=Shalini, custCity=Chennai, custAge=60] Customer [custName=Shalini, custCity=Chennai, custAge=70] Customer [custName=Simran, custCity=Bangalore, custAge=37] Customer [custName=Sneha, custCity=Pune, custAge=62] Customer [custName=Sneha, custCity=Pune, custAge=73] Customer [custName=Trisha, custCity=Hyderabad, custAge=52] Customer [custName=Trisha, custCity=Mangalore, custAge=45]

    2.3 Inline sorting using Comparator :

    • In this approach, we are going to pass 3 Comparators to sorted() method using thenComparing() method one-by-one using Method Reference

    CustomerSortingUsingJava8Comparing.java

    package net.bench.resources.stream.sorting.multiple.fields; import java.util.Arrays; import java.util.Comparator; import java.util.List; import java.util.stream.Collectors; public class CustomerSortingUsingJava8Comparing < // customer list private static ListgetUnSortedCustomers() < return Arrays.asList( new Customer("Shalini", "Chennai", 60), new Customer("Sneha", "Pune", 73), new Customer("Simran", "Bangalore", 37), new Customer("Trisha", "Hyderabad", 52), new Customer("Shalini", "Chennai", 70), new Customer("Abirami", "Bangalore", 48), new Customer("Trisha", "Mangalore", 45), new Customer("Sneha", "Pune", 62), new Customer("Shalini", "Chennai", 50) ); >// main() method public static void main(String[] args) < // get customer list ListunsortedCustomerList = getUnSortedCustomers(); System.out.println("Before Sorting: Customer list :- \n"); unsortedCustomerList.stream().forEach(System.out::println); System.out.println("\n\nSorted Customer list on multiple fields :- \n"); // inline - sorting on multiple fields List sortedCustomerList = unsortedCustomerList .stream() .sorted( Comparator.comparing(Customer::getCustName) // 1st compare Name .thenComparing(Customer::getCustCity) // then 2nd compare City .thenComparing(Customer::getCustAge)) // then 3rd compare Age .collect(Collectors.toList()); // collect sorted customers to new list // print new list to console using forEach() sortedCustomerList.stream().forEach(System.out::println); > >

    Output:

    Before Sorting: Customer list :- Customer [custName=Shalini, custCity=Chennai, custAge=60] Customer [custName=Sneha, custCity=Pune, custAge=73] Customer [custName=Simran, custCity=Bangalore, custAge=37] Customer [custName=Trisha, custCity=Hyderabad, custAge=52] Customer [custName=Shalini, custCity=Chennai, custAge=70] Customer [custName=Abirami, custCity=Bangalore, custAge=48] Customer [custName=Trisha, custCity=Mangalore, custAge=45] Customer [custName=Sneha, custCity=Pune, custAge=62] Customer [custName=Shalini, custCity=Chennai, custAge=50] Sorted Customer list on multiple fields :- Customer [custName=Abirami, custCity=Bangalore, custAge=48] Customer [custName=Shalini, custCity=Chennai, custAge=50] Customer [custName=Shalini, custCity=Chennai, custAge=60] Customer [custName=Shalini, custCity=Chennai, custAge=70] Customer [custName=Simran, custCity=Bangalore, custAge=37] Customer [custName=Sneha, custCity=Pune, custAge=62] Customer [custName=Sneha, custCity=Pune, custAge=73] Customer [custName=Trisha, custCity=Hyderabad, custAge=52] Customer [custName=Trisha, custCity=Mangalore, custAge=45]

    2.4 Collections.sort() method :

    • In this approach, we are going to define 3 Comparators namely nameComparator, cityComparator and ageComparator using Method Reference
    • Finally, we are going to create another composition Comparator using thenComparing() method passing 3 comparators one-by-one
    • Customer list and composition Comparator are passed as arguments to Collections.sort() method for multiple field sorting

    MultipleSortingUsingCollectionsSortMethod.java

    package net.bench.resources.stream.sorting.multiple.fields; import java.util.Arrays; import java.util.Collections; import java.util.Comparator; import java.util.List; public class MultipleSortingUsingCollectionsSortMethod < // customer list private static ListgetUnSortedCustomers() < return Arrays.asList( new Customer("Shalini", "Chennai", 60), new Customer("Sneha", "Pune", 73), new Customer("Simran", "Bangalore", 37), new Customer("Trisha", "Hyderabad", 52), new Customer("Shalini", "Chennai", 70), new Customer("Abirami", "Bangalore", 48), new Customer("Trisha", "Mangalore", 45), new Customer("Sneha", "Pune", 62), new Customer("Shalini", "Chennai", 50) ); >public static void main(String[] args) < // get customer list ListcustomerList = getUnSortedCustomers(); System.out.println("Before Sorting: Customer list :- \n"); customerList.stream().forEach(System.out::println); System.out.println("\n\nSorting Customer list using Collection.sort() :- \n"); // 1. customer Name comparator Comparator nameComparator = Comparator .comparing(Customer::getCustName); // 2. customer City comparator Comparator cityComparator = Comparator .comparing(Customer::getCustCity); // 3. customer Age comparator Comparator ageComparator = Comparator .comparing(Customer::getCustAge); // 4. composition of above 3 Comparators Comparator multipleFieldComparator = nameComparator // 1st compare Name .thenComparing(cityComparator) // then 2nd compare City .thenComparing(ageComparator); // then 3rd compare Age // sorting on multiple fields using composition Comparator Collections.sort(customerList, multipleFieldComparator); // print to console customerList.forEach(System.out::println); > >

    Output:

    Before Sorting: Customer list :- Customer [custName=Shalini, custCity=Chennai, custAge=60] Customer [custName=Sneha, custCity=Pune, custAge=73] Customer [custName=Simran, custCity=Bangalore, custAge=37] Customer [custName=Trisha, custCity=Hyderabad, custAge=52] Customer [custName=Shalini, custCity=Chennai, custAge=70] Customer [custName=Abirami, custCity=Bangalore, custAge=48] Customer [custName=Trisha, custCity=Mangalore, custAge=45] Customer [custName=Sneha, custCity=Pune, custAge=62] Customer [custName=Shalini, custCity=Chennai, custAge=50] Sorting Customer list using Collection.sort() :- Customer [custName=Abirami, custCity=Bangalore, custAge=48] Customer [custName=Shalini, custCity=Chennai, custAge=50] Customer [custName=Shalini, custCity=Chennai, custAge=60] Customer [custName=Shalini, custCity=Chennai, custAge=70] Customer [custName=Simran, custCity=Bangalore, custAge=37] Customer [custName=Sneha, custCity=Pune, custAge=62] Customer [custName=Sneha, custCity=Pune, custAge=73] Customer [custName=Trisha, custCity=Hyderabad, custAge=52] Customer [custName=Trisha, custCity=Mangalore, custAge=45]

    2.5 Arrays.sort() method :

    • In this approach, we are going to define 3 Comparators namely nameComparator, cityComparator and ageComparator using Method Reference
    • Finally, we are going to create another composition Comparator using thenComparing() method passing 3 comparators one-by-one
    • Customer[] array and composition Comparator are passed as arguments to Arrays.sort() method for multiple field sorting
    • Note: we can also print Arrays in the following manner Arrays.toString(customerArr) but result will be in one single line

    MultipleSortingUsingArraysSortMethod.java

    package net.bench.resources.stream.sorting.multiple.fields; import java.util.Arrays; import java.util.Comparator; public class MultipleSortingUsingArraysSortMethod < // customer list private static Customer[] getUnSortedCustomers() < return new Customer[] < new Customer("Shalini", "Chennai", 60), new Customer("Sneha", "Pune", 73), new Customer("Simran", "Bangalore", 37), new Customer("Trisha", "Hyderabad", 52), new Customer("Shalini", "Chennai", 70), new Customer("Abirami", "Bangalore", 48), new Customer("Trisha", "Mangalore", 45), new Customer("Sneha", "Pune", 62), new Customer("Shalini", "Chennai", 50) >; > public static void main(String[] args) < // get customer list Customer[] customerArr = getUnSortedCustomers(); System.out.println("Before Sorting: Customer Array :- \n"); Arrays.stream(customerArr).forEach(System.out::println); System.out.println("\n\nSorting Customer[] using Arrays.sort() :- \n"); // 1. customer Name comparator ComparatornameComparator = Comparator .comparing(Customer::getCustName); // 2. customer City comparator Comparator cityComparator = Comparator .comparing(Customer::getCustCity); // 3. customer Age comparator Comparator ageComparator = Comparator .comparing(Customer::getCustAge); // 4. composition of above 3 Comparators Comparator multipleFieldComparator = nameComparator // 1st compare Name .thenComparing(cityComparator) // then 2nd compare City .thenComparing(ageComparator); // then 3rd compare Age // sorting on multiple fields using composition Comparator Arrays.sort(customerArr, multipleFieldComparator); // print to console Arrays.stream(customerArr).forEach(System.out::println); > >

    Output:

    Before Sorting: Customer Array :- Customer [custName=Shalini, custCity=Chennai, custAge=60] Customer [custName=Sneha, custCity=Pune, custAge=73] Customer [custName=Simran, custCity=Bangalore, custAge=37] Customer [custName=Trisha, custCity=Hyderabad, custAge=52] Customer [custName=Shalini, custCity=Chennai, custAge=70] Customer [custName=Abirami, custCity=Bangalore, custAge=48] Customer [custName=Trisha, custCity=Mangalore, custAge=45] Customer [custName=Sneha, custCity=Pune, custAge=62] Customer [custName=Shalini, custCity=Chennai, custAge=50] Sorting Customer[] using Arrays.sort() :- Customer [custName=Abirami, custCity=Bangalore, custAge=48] Customer [custName=Shalini, custCity=Chennai, custAge=50] Customer [custName=Shalini, custCity=Chennai, custAge=60] Customer [custName=Shalini, custCity=Chennai, custAge=70] Customer [custName=Simran, custCity=Bangalore, custAge=37] Customer [custName=Sneha, custCity=Pune, custAge=62] Customer [custName=Sneha, custCity=Pune, custAge=73] Customer [custName=Trisha, custCity=Hyderabad, custAge=52] Customer [custName=Trisha, custCity=Mangalore, custAge=45]

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    References :

    Happy Coding !!
    Happy Learning !!

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