Java 8 Comparator with lambda

Java/comparator-lambda-expression/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.javadevjournal</groupId>
+    <artifactId>comparator-lambda-expression</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <properties>
+        <maven.compiler.source>15</maven.compiler.source>
+        <maven.compiler.target>15</maven.compiler.target>
+    </properties>
+    <dependencies>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>1.18.16</version>
+            <scope>provided</scope>
+        </dependency>
+    </dependencies>
+</project>

Java/comparator-lambda-expression/src/main/java/com/javadevjournal/CustomerService.java

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+package com.javadevjournal;
+
+import com.javadevjournal.data.Customer;
+
+import java.util.*;
+
+public class CustomerService {
+
+    public static void main(String[] args) {
+
+        sortByAge();
+        sortByFirstAndSecondName();
+        sortInReverseOrder();
+    }
+
+    private static void sortInReverseOrder(){
+        List<Customer> customerList = getCustomers();
+        Comparator<Customer> customerComparator = Comparator.comparing(e-> e.getAge());
+        customerList.sort(customerComparator.reversed());
+        customerList.forEach(System.out::println);
+    }
+
+    private static void sortByFirstAndSecondName(){
+        List<Customer> customers = getCustomers();
+
+        //Let's get the comparator
+        Comparator<Customer> comparator = Comparator.comparing(Customer::getFirstName)
+                .thenComparing(Customer::getLastName);
+
+        customers.sort(comparator);
+
+        //output
+        customers.forEach(System.out::println);
+    }
+
+    private static void sortByAge(){
+        List<Customer> customers = getCustomers();
+        customers.sort(Comparator.comparing(Customer::getAge));
+        //customers.forEach(System.out::println);
+
+        //option 2
+        List<Customer> customers1 = getCustomers();
+        customers1.sort(Comparator.comparing(e->e.getAge()));
+        customers1.forEach(System.out::println);
+
+        //option 3 if we know the type
+        customers.sort(Comparator.comparingInt(Customer::getAge));
+
+        //pure lambda expression
+        Collections.sort(customers, (c1, c2) -> c1.getAge() - c1.getAge()); //we careful when using this as it can cause overflow
+    }
+
+    private static List<Customer> getCustomers(){
+
+        List<Customer> customers = new ArrayList();
+
+        customers.add(Customer.builder()
+                .firstName("Robert").lastName("Hickle")
+                .age(62).email("abc@demo1.com")
+                .build());
+
+        customers.add(Customer.builder()
+                .firstName("Sandra").lastName("Hadleigh")
+                .age(21).email("Sandra@demo.com")
+                .build());
+
+        customers.add(Customer.builder()
+                .firstName("Miller").lastName("Gerty")
+                .age(41).email("miller@demo.com")
+                .build());
+
+        customers.add(Customer.builder()
+                .firstName("Milton").lastName("Arnison")
+                .age(30).email("arnison@demo.com")
+                .build());
+
+        customers.add(Customer.builder()
+                .firstName("Crissy").lastName("Finch")
+                .age(35).email("crissy@demo.com")
+                .build());
+
+        return customers;
+    }
+}

Java/comparator-lambda-expression/src/main/java/com/javadevjournal/data/Customer.java

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+package com.javadevjournal.data;
+
+import lombok.Builder;
+import lombok.Data;
+
+import java.io.Serializable;
+
+@Data
+@Builder
+public class Customer implements Serializable {
+
+    private String firstName;
+    private String lastName;
+    private String email;
+    private int age;
+}