In this article we will discuss different ways to sort LinkedList elements using Java 8
Before proceeding with this sorting examples understand below items,
- What is List ?
- What is LinkedList ?
- Iterating and printing LinkedList – 5 ways
- How to iterate through LinkedList in reverse order
- Sorting LinkedList – 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 LinkedList of Integer numbers
- A LinkedList contains integer numbers in insertion-order
- We are sorting these integer numbers in natural order (or ascending order) using Java 8 Stream’s sorted() method
SortLinkedListOfIntegerUsingStream.java
package net.bench.resources.sort.linkedlist;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;
import java.util.stream.Collectors;
public class SortLinkedListOfIntegerUsingStream {
public static void main(String[] args) {
// 1. create LinkedList
List<Integer> numbers = new LinkedList<>();
// 1.2 add integer numbers to LL
numbers.add(87);
numbers.add(18);
numbers.add(98);
numbers.add(64);
numbers.add(25);
numbers.add(77);
numbers.add(54);
// 1.3 original LinkedList in insertion order
System.out.println("1. Original LinkedList<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 "
+ "LinkedList<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 "
+ "LinkedList<Integer> :- \n");
reverseSortedNumber.forEach(System.out::println);
}
}
Output:
1. Original LinkedList<Integer> as per insertion-order :-
87
18
98
64
25
77
54
2. Natural order of LinkedList<Integer> :-
18
25
54
64
77
87
98
3. Reverse order of LinkedList<Integer> :-
98
87
77
64
54
25
18
1.2 Sorting LinkedList of String elements
- A LinkedList contains String elements in insertion-order
- We are sorting these String elements in alphabetical order using Java 8 Stream’s sorted() method
SortLinkedListOfStringUsingStream.java
package net.bench.resources.sort.linkedlist;
import java.util.LinkedList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
public class SortLinkedListOfStringUsingStream {
public static void main(String[] args) {
// 1. create LinkedList
List<String> names = new LinkedList<>();
// 1.1 add names to LL
names.add("Karthik");
names.add("Nagarjuna");
names.add("Ramki");
names.add("Surya");
names.add("Ajith");
names.add("Prasanna");
// 1.2 original LinkedList in insertion order
System.out.println("1. Original LinkedList<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 LinkedList<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 LinkedList<String> :- \n");
reverseSortedNames.forEach(System.out::println);
}
}
Output:
1. Original LinkedList<String> as per insertion-order :-
Karthik
Nagarjuna
Ramki
Surya
Ajith
Prasanna
2. Alphabetically sorted-order of LinkedList<String> :-
Ajith
Karthik
Nagarjuna
Prasanna
Ramki
Surya
3. Reverse alphabetically sorted-order of LinkedList<String> :-
Surya
Ramki
Prasanna
Nagarjuna
Karthik
Ajith
1.3 Sorting LinkedList of Student objects
- A LinkedList contains Student objects with attributes such as Id, name and their age in insertion-order
- We are sorting these Student objects in natural order according to their age 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()
}
SortLinkedListOfStudentsUsingStreamSorted.java
package net.bench.resources.sort.linkedlist;
import java.util.LinkedList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
public class SortLinkedListOfStudentsUsingStreamSorted {
public static void main(String[] args) {
// 1. create LinkedList
List<Student> students = new LinkedList<>();
// 1.1 add Students to LL
students.add(new Student(2063, "Pravin", 35));
students.add(new Student(2097, "Shweta", 32));
students.add(new Student(2019, "Sachin", 28));
students.add(new Student(2023, "Kalpana", 27));
students.add(new Student(2045, "Rajdeepan", 31));
students.add(new Student(2073, "Sneha", 24));
// 1.2 original LinkedList in insertion order
System.out.println("1. Original LinkedList "
+ "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 LinkedList -"
+ " 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 LinkedList -"
+ " according to Id :- \n");
reverseSortedStudents.forEach(System.out::println);
}
}
Output:
1. Original LinkedList as per insertion-order :-
Student [rollNumber=2063, name=Pravin, age=35]
Student [rollNumber=2097, name=Shweta, age=32]
Student [rollNumber=2019, name=Sachin, age=28]
Student [rollNumber=2023, name=Kalpana, age=27]
Student [rollNumber=2045, name=Rajdeepan, age=31]
Student [rollNumber=2073, name=Sneha, age=24]
2. Sorted Student LinkedList - according to Age :-
Student [rollNumber=2073, name=Sneha, age=24]
Student [rollNumber=2023, name=Kalpana, age=27]
Student [rollNumber=2019, name=Sachin, age=28]
Student [rollNumber=2045, name=Rajdeepan, age=31]
Student [rollNumber=2097, name=Shweta, age=32]
Student [rollNumber=2063, name=Pravin, age=35]
3. Reverse sorted Student LinkedList - according to Id :-
Student [rollNumber=2097, name=Shweta, age=32]
Student [rollNumber=2073, name=Sneha, age=24]
Student [rollNumber=2063, name=Pravin, age=35]
Student [rollNumber=2045, name=Rajdeepan, age=31]
Student [rollNumber=2023, name=Kalpana, age=27]
Student [rollNumber=2019, name=Sachin, age=28]
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 LinkedList of Integer numbers
- A LinkedList contains integer numbers in insertion-order
- We are sorting these integer numbers in natural order (or ascending order) using Java 8 List’s sort() method
SortLinkedListOfIntegerUsingListSortMethod.java
package net.bench.resources.sort.linkedlist;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;
public class SortLinkedListOfIntegerUsingListSortMethod {
public static void main(String[] args) {
// 1. create LinkedList
List<Integer> numbers = new LinkedList<>();
// 1.2 add integer numbers to AL
numbers.add(87);
numbers.add(18);
numbers.add(98);
numbers.add(64);
numbers.add(25);
numbers.add(77);
numbers.add(54);
// 1.3 original LinkedList in insertion order
System.out.println("1. Original LinkedList<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 "
+ "LinkedList<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 "
+ "LinkedList<Integer> :- \n");
numbers.forEach(System.out::println);
}
}
Output:
1. Original LinkedList<Integer> as per insertion-order :-
87
18
98
64
25
77
54
2. Natural order of LinkedList<Integer> :-
18
25
54
64
77
87
98
3. Reverse order of LinkedList<Integer> :-
98
87
77
64
54
25
18
2.2 Sorting LinkedList of String elements
- A LinkedList contains String elements in insertion-order
- We are sorting these String elements in alphabetical order using Java 8 List’s sort() method
SortLinkedListOfStringUsingListSortMethod.java
package net.bench.resources.sort.linkedlist;
import java.util.LinkedList;
import java.util.Comparator;
import java.util.List;
public class SortLinkedListOfStringUsingListSortMethod {
public static void main(String[] args) {
// 1. create LinkedList
List<String> names = new LinkedList<>();
// 1.1 add names to LL
names.add("Karthik");
names.add("Nagarjuna");
names.add("Ramki");
names.add("Surya");
names.add("Ajith");
names.add("Prasanna");
// 1.2 original LinkedList as per insertion order
System.out.println("1. Original LinkedList<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 LinkedList<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 LinkedList<String> :- \n");
names.forEach(System.out::println);
}
}
Output:
1. Original LinkedList<String> as per insertion-order :-
Karthik
Nagarjuna
Ramki
Surya
Ajith
Prasanna
2. Alphabetically sorted-order of LinkedList<String> :-
Ajith
Karthik
Nagarjuna
Prasanna
Ramki
Surya
3. Reverse alphabetically sorted-order of LinkedList<String> :-
Surya
Ramki
Prasanna
Nagarjuna
Karthik
Ajith
2.3 Sorting LinkedList of Student objects
- A LinkedList contains Student objects with attributes such as Id, name and their age in insertion-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
SortLinkedListOfStudentsUsingListSortMethod.java
package net.bench.resources.sort.linkedlist;
import java.util.LinkedList;
import java.util.Comparator;
import java.util.List;
public class SortLinkedListOfStudentsUsingListSortMethod {
public static void main(String[] args) {
// 1. create LinkedList
List<Student> students = new LinkedList<>();
// 1.1 add Students to LL
students.add(new Student(2063, "Pravin", 35));
students.add(new Student(2097, "Shweta", 32));
students.add(new Student(2019, "Sachin", 28));
students.add(new Student(2023, "Kalpana", 27));
students.add(new Student(2045, "Rajdeepan", 31));
students.add(new Student(2073, "Sneha", 24));
// 1.2 original LinkedList in insertion order
System.out.println("1. Original LinkedList "
+ "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 LinkedList -"
+ " 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 LinkedList -"
+ " according to Id :- \n");
students.forEach(System.out::println);
}
}
Output:
1. Original LinkedList as per insertion-order :-
Student [rollNumber=2063, name=Pravin, age=35]
Student [rollNumber=2097, name=Shweta, age=32]
Student [rollNumber=2019, name=Sachin, age=28]
Student [rollNumber=2023, name=Kalpana, age=27]
Student [rollNumber=2045, name=Rajdeepan, age=31]
Student [rollNumber=2073, name=Sneha, age=24]
2. Sorted Student LinkedList - according to Age :-
Student [rollNumber=2073, name=Sneha, age=24]
Student [rollNumber=2023, name=Kalpana, age=27]
Student [rollNumber=2019, name=Sachin, age=28]
Student [rollNumber=2045, name=Rajdeepan, age=31]
Student [rollNumber=2097, name=Shweta, age=32]
Student [rollNumber=2063, name=Pravin, age=35]
3. Reverse sorted Student LinkedList - according to Id :-
Student [rollNumber=2097, name=Shweta, age=32]
Student [rollNumber=2073, name=Sneha, age=24]
Student [rollNumber=2063, name=Pravin, age=35]
Student [rollNumber=2045, name=Rajdeepan, age=31]
Student [rollNumber=2023, name=Kalpana, age=27]
Student [rollNumber=2019, name=Sachin, age=28]
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 !!