In this article we will discuss different ways to sort ArrayList elements using Java 8
Before proceeding with this sorting examples understand below items,
- What is List ?
- What is ArrayList ?
- Iterating and printing List
- 5 ways of iterating ArrayList
- Sorting ArrayList – before Java 8
- Sorting ArrayList in descending order – before Java 8
1. Stream.sorted() method :
- This Stream method is an stateful intermediate operation which sorts elements present in the stream according to natural order
- If elements present in the stream aren’t Comparable then java.lang.ClassCastException is thrown when final terminal operation is executed
- For ordered streams, the sort is stable
- For unordered streams, no stability guarantees are made
- Method signature 1 :- Stream<T> sorted()
- Method signature 2 :- Stream<T> sorted(Comparator<? super T> comparator)
1.1 Sorting ArrayList of Integer numbers :
- An ArrayList contains integers numbers in random order
- We are sorting these integer numbers in natural order (or ascending order) using Java 8 Stream’s sorted() method
SortArrayListOfIntegerUsingStream.java
package net.bench.resources.sort.arraylist;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
public class SortArrayListOfIntegerUsingStream {
public static void main(String[] args) {
// 1. create ArrayList
List<Integer> numbers = new ArrayList<>();
// 1.2 add integer numbers to AL
numbers.add(86);
numbers.add(19);
numbers.add(97);
numbers.add(63);
numbers.add(23);
numbers.add(92);
numbers.add(94);
// 1.3 original ArrayList in insertion order
System.out.println("1. Original ArrayList<Integer> "
+ "as per insertion-order :- \n");
numbers.forEach(System.out::println);
// 2. Stream.sorted() - natural order
List<Integer> sortedNumbers = numbers
.stream()
.sorted()
.collect(Collectors.toList());
// 2.1 print to console
System.out.println("\n2. Natural order of "
+ "ArrayList<Integer> :- \n");
sortedNumbers.forEach(System.out::println);
// 3. Stream.sorted() - reverse order
List<Integer> reverseSortedNumber = numbers
.stream()
.sorted(Comparator.reverseOrder())
.collect(Collectors.toList());
// 3.1 print to console
System.out.println("\n3. Reverse order of "
+ "ArrayList<Integer> :- \n");
reverseSortedNumber.forEach(System.out::println);
}
}
Output:
1. Original ArrayList<Integer> as per insertion-order :-
86
19
97
63
23
92
94
2. Natural order of ArrayList<Integer> :-
19
23
63
86
92
94
97
3. Reverse order of ArrayList<Integer> :-
97
94
92
86
63
23
19
1.2 Sorting ArrayList of String elements :
- An ArrayList contains String elements in random order
- We are sorting these String elements in alphabetical order using Java 8 Stream’s sorted() method
SortArrayListOfStringUsingStream.java
package net.bench.resources.sort.arraylist;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
public class SortArrayListOfStringUsingStream {
public static void main(String[] args) {
// 1. create ArrayList
List<String> names = new ArrayList<>();
// 1.1 add names to AL
names.add("Rambha");
names.add("Amala");
names.add("Urvashi");
names.add("Meghana");
names.add("Pavithra");
names.add("Sneha");
// 1.2 original ArrayList in insertion order
System.out.println("1. Original ArrayList<String> "
+ "as per insertion-order :- \n");
names.forEach(System.out::println);
// 2. sort using Stream - alphabetical order
List<String> sortedNames = names
.stream()
.sorted()
.collect(Collectors.toList());
// 2.1 print to console
System.out.println("\n2. Alphabetically sorted-order "
+ "of ArrayList<String> :- \n");
sortedNames.forEach(System.out::println);
// 3. sort using Stream - reverse alphabetical order
List<String> reverseSortedNames = names
.stream()
.sorted(Comparator.reverseOrder())
.collect(Collectors.toList());
// 3.1 print to console
System.out.println("\n3. Reverse alphabetically sorted-order "
+ "of ArrayList<String> :- \n");
reverseSortedNames.forEach(System.out::println);
}
}
Output:
1. Original ArrayList<String> as per insertion-order :-
Rambha
Amala
Urvashi
Meghana
Pavithra
Sneha
2. Alphabetically sorted-order of ArrayList<String> :-
Amala
Meghana
Pavithra
Rambha
Sneha
Urvashi
3. Reverse alphabetically sorted-order of ArrayList<String> :-
Urvashi
Sneha
Rambha
Pavithra
Meghana
Amala
1.3 Sorting ArrayList of Students objects :
- An ArrayList contains Student objects with attributes such as Id, name and their age in random order
- We are sorting these Student objects according to their age in natural order and their Id in descending order using Java 8 Stream’s sorted() method
Student.java
package net.bench.resources.sort.linkedlist;
public class Student {
// member variables
private int rollNumber;
private String name;
private int age;
// constructors
// getters & setters
// toString()
}
SortArrayListOfStudentsUsingStreamSorted.java
package net.bench.resources.sort.arraylist;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
public class SortArrayListOfStudentsUsingStreamSorted {
public static void main(String[] args) {
// 1. create ArrayList
List<Student> students = new ArrayList<>();
// 1.1 add Students to AL
students.add(new Student(101, "Rambha", 46));
students.add(new Student(102, "Amala", 57));
students.add(new Student(103, "Urvashi", 49));
students.add(new Student(104, "Meghana", 24));
students.add(new Student(105, "Pavithra", 29));
students.add(new Student(106, "Sneha", 38));
// 1.2 original ArrayList in insertion order
System.out.println("1. Original ArrayList "
+ "as per insertion-order :- \n");
students.forEach(System.out::println);
// 2. sort using Stream - increasing-order of Age
List<Student> sortedStudents = students
.stream()
.sorted(Comparator.comparingInt(Student::getAge))
.collect(Collectors.toList());
// 2.1 print to console
System.out.println("\n2. Sorted Student ArrayList -"
+ " according to Age :- \n");
sortedStudents.forEach(System.out::println);
// 3. sort using Stream - reverse-order of Roll Id
List<Student> reverseSortedStudents = students
.stream()
.sorted(Comparator.comparingInt(Student::getRollId).reversed())
.collect(Collectors.toList());
// 3.1 print to console
System.out.println("\n3. Reverse sorted Student ArrayList -"
+ " according to Id :- \n");
reverseSortedStudents.forEach(System.out::println);
}
}
Output:
1. Original ArrayList as per insertion-order :-
Student [rollNumber=101, name=Rambha, age=46]
Student [rollNumber=102, name=Amala, age=57]
Student [rollNumber=103, name=Urvashi, age=49]
Student [rollNumber=104, name=Meghana, age=24]
Student [rollNumber=105, name=Pavithra, age=29]
Student [rollNumber=106, name=Sneha, age=38]
2. Sorted Student ArrayList - according to Age :-
Student [rollNumber=104, name=Meghana, age=24]
Student [rollNumber=105, name=Pavithra, age=29]
Student [rollNumber=106, name=Sneha, age=38]
Student [rollNumber=101, name=Rambha, age=46]
Student [rollNumber=103, name=Urvashi, age=49]
Student [rollNumber=102, name=Amala, age=57]
3. Reverse sorted Student ArrayList - according to Id :-
Student [rollNumber=106, name=Sneha, age=38]
Student [rollNumber=105, name=Pavithra, age=29]
Student [rollNumber=104, name=Meghana, age=24]
Student [rollNumber=103, name=Urvashi, age=49]
Student [rollNumber=102, name=Amala, age=57]
Student [rollNumber=101, name=Rambha, age=46]
2. List.sort() method :
- Sorts this list according to the order induced by the specified Comparator
- All elements in this list must be mutually comparable using the specified comparator
- That is, c.compare(e1, e1) must not throw a
ClassCastExceptionfor any elementse1ande2in the list - If the specified comparator is
nullthen all elements in this list must implement theComparableinterface and the elements’ natural ordering should be used - Method signature :- default void sort(Comparator<? super E> comparator)
2.1 Sorting ArrayList of Integer numbers :
- An ArrayList contains integers numbers in random order
- We are sorting these integer numbers in natural order (or ascending order) using Java 8 List’s sort() method
SortArrayListOfIntegerUsingListSortMethod.java
package net.bench.resources.sort.arraylist;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
public class SortArrayListOfIntegerUsingListSortMethod {
public static void main(String[] args) {
// 1. create ArrayList
List<Integer> numbers = new ArrayList<>();
// 1.2 add integer numbers to AL
numbers.add(86);
numbers.add(19);
numbers.add(97);
numbers.add(63);
numbers.add(23);
numbers.add(92);
numbers.add(94);
// 1.3 original ArrayList in insertion order
System.out.println("1. Original ArrayList<Integer> "
+ "as per insertion-order :- \n");
numbers.forEach(System.out::println);
// 2. List.sorted() - natural order
numbers.sort(Comparator.naturalOrder());
// 2.1 print to console
System.out.println("\n2. Natural order of "
+ "ArrayList<Integer> :- \n");
numbers.forEach(System.out::println);
// 3. List.sorted() - reverse order
numbers.sort(Comparator.reverseOrder());
// 3.1 print to console
System.out.println("\n3. Reverse order of "
+ "ArrayList<Integer> :- \n");
numbers.forEach(System.out::println);
}
}
Output:
1. Original ArrayList<Integer> as per insertion-order :-
86
19
97
63
23
92
94
2. Natural order of ArrayList<Integer> :-
19
23
63
86
92
94
97
3. Reverse order of ArrayList<Integer> :-
97
94
92
86
63
23
19
2.2 Sorting ArrayList of String elements :
- An ArrayList contains String elements in random order
- We are sorting these String elements in alphabetical order using Java 8 List’s sort() method
SortArrayListOfStringUsingListSortMethod.java
package net.bench.resources.sort.arraylist;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
public class SortArrayListOfStringUsingListSortMethod {
public static void main(String[] args) {
// 1. create ArrayList
List<String> names = new ArrayList<>();
// 1.1 add names to AL
names.add("Ramki");
names.add("Abbas");
names.add("Ulaganayagan");
names.add("Mohanlal");
names.add("PrithiviRaj");
names.add("Surya");
// 1.2 original ArrayList as per insertion order
System.out.println("1. Original ArrayList<String> "
+ "as per insertion-order :- \n");
names.forEach(System.out::println);
// 2. List.sort() - alphabetical order
names.sort(Comparator.naturalOrder());
// 2.1 print to console
System.out.println("\n2. Alphabetically sorted-order "
+ "of ArrayList<String> :- \n");
names.forEach(System.out::println);
// 3. List.sort() - reverse alphabetical order
names.sort(Comparator.reverseOrder());
// 3.1 print to console
System.out.println("\n3. Reverse alphabetically sorted-order "
+ "of ArrayList<String> :- \n");
names.forEach(System.out::println);
}
}
Output:
1. Original ArrayList<String> as per insertion-order :-
Ramki
Abbas
Ulaganayagan
Mohanlal
PrithiviRaj
Surya
2. Alphabetically sorted-order of ArrayList<String> :-
Abbas
Mohanlal
PrithiviRaj
Ramki
Surya
Ulaganayagan
3. Reverse alphabetically sorted-order of ArrayList<String> :-
Ulaganayagan
Surya
Ramki
PrithiviRaj
Mohanlal
Abbas
2.3 Sorting ArrayList of Students objects :
- An ArrayList contains Student objects with attributes such as Id, name and their age in random order
- We are sorting these Student objects according to their age in natural order and their Id in descending order using Java 8 List’s sort() method
SortArrayListOfStudentsUsingListSortMethod.java
package net.bench.resources.sort.arraylist;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
public class SortArrayListOfStudentsUsingListSortMethod {
public static void main(String[] args) {
// 1. create ArrayList
List<Student> students = new ArrayList<>();
// 1.1 add Students to AL
students.add(new Student(101, "Rambha", 46));
students.add(new Student(102, "Amala", 57));
students.add(new Student(103, "Urvashi", 49));
students.add(new Student(104, "Meghana", 24));
students.add(new Student(105, "Pavithra", 29));
students.add(new Student(106, "Sneha", 38));
// 1.2 original ArrayList in insertion order
System.out.println("1. Original ArrayList "
+ "as per insertion-order :- \n");
students.forEach(System.out::println);
// 2. List.sort() - increasing-order of Age
students.sort(Comparator
.comparing(Student::getAge));
// 2.1 print to console
System.out.println("\n2. Sorted Student ArrayList -"
+ " according to Age :- \n");
students.forEach(System.out::println);
// 3. List.sort() - reverse-order of Roll Id
students.sort(Comparator
.comparingInt(Student::getRollId).reversed());
// 3.1 print to console
System.out.println("\n3. Reverse sorted Student ArrayList -"
+ " according to Id :- \n");
students.forEach(System.out::println);
}
}
Output:
1. Original ArrayList as per insertion-order :-
Student [rollNumber=101, name=Rambha, age=46]
Student [rollNumber=102, name=Amala, age=57]
Student [rollNumber=103, name=Urvashi, age=49]
Student [rollNumber=104, name=Meghana, age=24]
Student [rollNumber=105, name=Pavithra, age=29]
Student [rollNumber=106, name=Sneha, age=38]
2. Sorted Student ArrayList - according to Age :-
Student [rollNumber=104, name=Meghana, age=24]
Student [rollNumber=105, name=Pavithra, age=29]
Student [rollNumber=106, name=Sneha, age=38]
Student [rollNumber=101, name=Rambha, age=46]
Student [rollNumber=103, name=Urvashi, age=49]
Student [rollNumber=102, name=Amala, age=57]
3. Reverse sorted Student ArrayList - according to Id :-
Student [rollNumber=106, name=Sneha, age=38]
Student [rollNumber=105, name=Pavithra, age=29]
Student [rollNumber=104, name=Meghana, age=24]
Student [rollNumber=103, name=Urvashi, age=49]
Student [rollNumber=102, name=Amala, age=57]
Student [rollNumber=101, name=Rambha, age=46]
Related Articles:
- Java 8 – How to sort ArrayList elements
- Java 8 – Sorting List of primitive, String & Custom Objects
- Java 8 – Sorting ArrayList using sort() method of List
- Java 8 – How to sort LinkedList elements
- Java 8 – How to sort HashSet elements
- Java 8 – How to sort LinkedHashSet elements
- Java 8 – How to sort TreeSet in descending order
- Java 8 – How to sort List and Arrays with null values present
- Java 8 – How to sort Arrays in Ascending and Descending order ?
- Java 8 – Sorting list of objects on multiple fields (3-level attributes)
References:
- https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html
- https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#sorted–
- https://docs.oracle.com/javase/8/docs/api/java/util/List.html
- https://docs.oracle.com/javase/8/docs/api/java/util/List.html#sort-java.util.Comparator-
Happy Coding !!
Happy Learning !!