Sort a list in Java 8

Category : Java | Sub Category : Java8 Features | By Prasad Bonam Last updated: 2023-11-13 13:47:10 Viewed : 230

sort a list in Java 8:

To sort a list in Java 8, you can use the Collections.sort method or the List.sort method along with lambda expressions or method references for custom sorting. Here are examples using both approaches:

1. Using Collections.sort:

   javaCopy code
   import java.util.ArrayList;
   import java.util.Collections;
   import java.util.List;
   
   public class ListSortingExample {
       public static void main(String[] args) {
           List<String> names = new ArrayList<>();
           names.add("John");
           names.add("Jane");
           names.add("Bob");
           names.add("Alice");
   
           // Sorting using Collections.sort and lambda expression
           Collections.sort(names, (s1, s2) -> s1.compareTo(s2));
   
           // Output the sorted list
           System.out.println("Sorted List: " + names);
       }
   }
   

   Output:

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   Sorted List: [Alice, Bob, Jane, John]
   

2. Using List.sort:

   javaCopy code
   import java.util.ArrayList;
   import java.util.List;
   
   public class ListSortExample {
       public static void main(String[] args) {
           List<String> names = new ArrayList<>();
           names.add("John");
           names.add("Jane");
           names.add("Bob");
           names.add("Alice");
   
           // Sorting using List.sort and method reference
           names.sort(String::compareTo);
   
           // Output the sorted list
           System.out.println("Sorted List: " + names);
       }
   }
   

   Output:

   lessCopy code
   Sorted List: [Alice, Bob, Jane, John]
   

In both examples, the list of names is sorted alphabetically. You can customize the sorting logic by providing your own comparator inside the Collections.sort or List.sort method. The examples above use the natural order by using String::compareTo or (s1, s2) -> s1.compareTo(s2) for sorting strings.

If you have a list of Employee objects and you want to sort them based on the employee names in Java 8, you can use the List.sort method along with a comparator. Here is an example:

javaCopy code
import java.util.ArrayList;
import java.util.List;

public class EmployeeSortingExample {
    public static void main(String[] args) {
        // Sample list of Employee objects
        List<Employee> employees = new ArrayList<>();
        employees.add(new Employee("John", 30));
        employees.add(new Employee("Jane", 25));
        employees.add(new Employee("Bob", 35));
        employees.add(new Employee("Alice", 28));

        System.out.println("Unsorted List: " + employees);

        // Sorting the list by employee names
        employees.sort((e1, e2) -> e1.getName().compareTo(e2.getName()));

        System.out.println("Sorted List by Name: " + employees);
    }
}

class Employee {
    private String name;
    private int age;

    public Employee(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    @Override
    public String toString() {
        return "Employee{name= " + name + " , age=" + age +  } ;
    }
}

Output:

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Unsorted List: [Employee{name= John , age=30}, Employee{name= Jane , age=25}, Employee{name= Bob , age=35}, Employee{name= Alice , age=28}]
Sorted List by Name: [Employee{name= Alice , age=28}, Employee{name= Bob , age=35}, Employee{name=  Jane , age=25}, Employee{name= John , age=30}]

In this example:

• The Employee class has a name attribute.
• The list of Employee objects is sorted based on the names using the List.sort method and a lambda expression for the comparator. The comparator compares the names using the compareTo method.

You can customize the comparator based on your specific sorting requirements.