Sorting Array List In Ascending & Descending Order + Java 8 + Sorting Array List Of Custom Object

Hello everyone,

Greetings today!

Today we will see how to sort Array List in ascending & descending order.

To sort in ascending order we need to use Collections.sort method and to sort a list in descending we need to use Collection.reverseOrder as shown below.

package com.demo; import java.util.ArrayList; import java.util.Collections; import java.util.List; public class SortingDemo { public static void main(String[] args) { List<String> strings=new ArrayList<String>(); strings.add("Dragon Fruit"); strings.add("Apple"); strings.add("Strawberries"); strings.add("Oranges"); System.out.println("Before sorting "+strings.toString()); Collections.sort(strings); System.out.println("After sorting "+strings.toString()); Collections.sort(strings,Collections.reverseOrder()); System.out.println("After sorting in desc order"+strings); } }

Let's look at how to sort lists in Java 8 in both ascending and descending order.

package com.demo; import java.util.ArrayList; import java.util.Collections; import java.util.List; import java.util.stream.Collectors; public class SortingDemo { public static void main(String[] args) { List<String> strings=new ArrayList<String>(); strings.add("Dragon Fruit"); strings.add("Apple"); strings.add("Strawberries"); strings.add("Oranges"); System.out.println("Before sorting "+strings.toString()); List<String> sortedStrings= strings.stream().sorted().collect(Collectors.toList()); System.out.println("After sorting in Ascending "+sortedStrings); List<String> sortedDescList = strings.stream().sorted(Collections.reverseOrder()) .collect(Collectors.toList()); System.out.println("After sorting in descending order "+sortedDescList); } }

Now, let's look at how to sort an array list of custom objects in java and java 8.

For that let's create an Employee class and add a constructor & getter-setter.

package com.demo; public class Employee { private int employeeId; private String employeeName; private int employeeSalary; //TODO Add Getter & Setter public Employee(int employeeId, String employeeName, int employeeSalary) { super(); this.employeeId = employeeId; this.employeeName = employeeName; this.employeeSalary = employeeSalary; } @Override public String toString() { return "Employee [employeeId=" + employeeId + ", employeeName=" + employeeName + ", employeeSalary=" + employeeSalary + "]"; } public Employee() { } }

Now we must create a class that will implement Comparator; currently, I am demonstrating how to sort employees based on salary.

package com.demo; import java.util.Comparator; public class SalaryComparator implements Comparator<Employee>{ @Override public int compare(Employee emp1, Employee emp2) { return emp1.getEmployeeSalary()-emp2.getEmployeeSalary(); } }

Let us now look at how to sort. As we are sorting by salary, we will pass SalaryComparator.

package com.demo; import java.util.ArrayList; import java.util.Collections; import java.util.List; public class SortingDemo { public static void main(String[] args) { List<Employee> employees = new ArrayList<>(); Employee emp1 = new Employee(1, "Rajesh", 33000); Employee emp2 = new Employee(2, "Pritesh", 35000); Employee emp3 = new Employee(3, "Manoj", 29000); Employee emp4 = new Employee(4, "Santosh", 60000); employees.add(emp1); employees.add(emp2); employees.add(emp3); employees.add(emp4); Collections.sort(employees, new SalaryComparator()); System.out.println(employees); } }

 O/P

[Employee [employeeId=3, employeeName=Manoj, employeeSalary=29000],

Employee [employeeId=1, employeeName=Rajesh, employeeSalary=33000], 

Employee [employeeId=2, employeeName=Pritesh, employeeSalary=35000],

Employee [employeeId=4, employeeName=Santosh, employeeSalary=60000]]

Now, let's look at how to sort an array list of a custom object with different properties like salary and name in Java 8.

package com.demo; import java.util.ArrayList; import java.util.Comparator; import java.util.List; import java.util.stream.Collectors; public class SortingDemo { public static void main(String[] args) { List<Employee> employees = new ArrayList<>(); Employee emp1 = new Employee(1, "Rajesh", 33000); Employee emp2 = new Employee(2, "Pritesh", 35000); Employee emp3 = new Employee(3, "Manoj", 29000); Employee emp4 = new Employee(4, "Santosh", 60000); employees.add(emp1); employees.add(emp2); employees.add(emp3); employees.add(emp4); // Sorting in ascending order using salary List<Employee> empSalarySortedAsc = employees.stream().sorted(Comparator.comparingInt(Employee::getEmployeeSalary)) .collect(Collectors.toList()); System.out.println("Sorting by salary in ascending order"); empSalarySortedAsc.forEach(System.out::println); // Sorting in descending order using salary List<Employee> empSalarySortedDesc = employees.stream().sorted(Comparator.comparingInt(Employee::getEmployeeSalary) .reversed()).collect(Collectors.toList()); System.out.println("Sorting by salary in descending order"); empSalarySortedDesc.forEach(System.out::println); // Sorting in ascending order by employee name List<Employee> empNameSortedAsc =employees.stream().sorted(Comparator.comparing(Employee::getEmployeeName)) .collect(Collectors.toList()); System.out.println("Sorting by employee name in ascending order"); empNameSortedAsc.forEach(System.out::println); // Sorting in descending order by employee name List<Employee> empNameSortedDesc =employees.stream().sorted(Comparator.comparing(Employee::getEmployeeName) .reversed()).collect(Collectors.toList()); System.out.println("Sorting by employee name in descending order"); empNameSortedDesc.forEach(System.out::println); } }

Here is output

Sorting by salary in ascending order Employee [employeeId=3, employeeName=Manoj, employeeSalary=29000] Employee [employeeId=1, employeeName=Rajesh, employeeSalary=33000] Employee [employeeId=2, employeeName=Pritesh, employeeSalary=35000] Employee [employeeId=4, employeeName=Santosh, employeeSalary=60000] Sorting by salary in descending order Employee [employeeId=4, employeeName=Santosh, employeeSalary=60000] Employee [employeeId=2, employeeName=Pritesh, employeeSalary=35000] Employee [employeeId=1, employeeName=Rajesh, employeeSalary=33000] Employee [employeeId=3, employeeName=Manoj, employeeSalary=29000] Sorting by employee name in ascending order Employee [employeeId=3, employeeName=Manoj, employeeSalary=29000] Employee [employeeId=2, employeeName=Pritesh, employeeSalary=35000] Employee [employeeId=1, employeeName=Rajesh, employeeSalary=33000] Employee [employeeId=4, employeeName=Santosh, employeeSalary=60000] Sorting by employee name in descending order Employee [employeeId=4, employeeName=Santosh, employeeSalary=60000] Employee [employeeId=1, employeeName=Rajesh, employeeSalary=33000] Employee [employeeId=2, employeeName=Pritesh, employeeSalary=35000] Employee [employeeId=3, employeeName=Manoj, employeeSalary=29000]

Thanks 

Enjoy your learning!

Another post you can refer to is

Sorting HashMap By Key And Value + Java 8

Sorting HashSet In Ascending & Descending order + Java 8

Comparator and Comparable In Java + Difference Between Comparator and Comparable + Java 8

Java 8 Stream - Intermediate Operations With Examples

Java 8 Stream - Terminal Operations With Examples

For spring refer to Spring Tutorial