Merge pull request #43 from amitrp/aph-15360_sort_object_collections_with_multiple_fields

aph-15360 Sort Object Collections using multiple fields

Author: amitrp

README.md

@@ -125,6 +125,8 @@ This project contains Core Java code samples that are used as examples on [amitp
 
 ### [Case-Insensitive Search in Java ArrayLists](https://www.amitph.com/java-arraylists-case-insensitive-search/)
 
+### [Sorting Collection of Objects by Multiple Fields in Java](https://www.amitph.com/java-collection-sort-multiple-fields/)
+
 ## How to use
 *Clone the project using*
 ```

java-collections/README.md

@@ -88,6 +88,7 @@ This project contains Java Collections code samples that are used as examples on
 
 ### [Case-Insensitive Search in Java ArrayLists](https://www.amitph.com/java-arraylists-case-insensitive-search/)
 
+### [Sorting Collection of Objects by Multiple Fields in Java](https://www.amitph.com/java-collection-sort-multiple-fields/)
 
 ## How to use
 *Clone the project using*

java-collections/pom.xml

@@ -32,6 +32,11 @@
             <artifactId>commons-collections4</artifactId>
             <version>4.4</version>
         </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>3.12.0</version>
+        </dependency>
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>

java-collections/src/main/java/com/amitph/java/collections/MultiFieldSorter.java

@@ -0,0 +1,102 @@
+package com.amitph.java.collections;
+
+import com.google.common.collect.ComparisonChain;
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+import lombok.ToString;
+import org.apache.commons.lang3.builder.CompareToBuilder;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+
+@RequiredArgsConstructor
+public class MultiFieldSorter {
+    private final List<Student> collection = new ArrayList<>(List.of(
+            new Student(1L, "Ray", 18),
+            new Student(2L, "Bee", 18),
+            new Student(3L, "Ray", 17),
+            new Student(4L, "Bia", 15),
+            new Student(5L, "Ria", 15)
+    ));
+
+    public void sortUsingComparator_Field_by_Field() {
+        collection.sort(new SimpleComparator());
+        collection.forEach(System.out::println);
+    }
+
+    public void sortUsingComparator_Guava_ComparisonChain() {
+        collection.sort(new GuavaBasedComparator());
+        collection.forEach(System.out::println);
+    }
+
+    public void sortUsingComparator_Commons_CompareToBuilder() {
+        collection.sort(new ApacheCommonsBasedComparator());
+        collection.forEach(System.out::println);
+    }
+
+    public void sortUsingComparator_Comparing() {
+        collection.sort(Comparator
+                .comparing(Student::getName)
+                .thenComparing(Student::getAge));
+        collection.forEach(System.out::println);
+    }
+
+    public static void main(String[] a) {
+        MultiFieldSorter sorter = new MultiFieldSorter();
+
+        System.out.println("Custom Comparator - Simple");
+        sorter.sortUsingComparator_Field_by_Field();
+
+        System.out.println();
+        System.out.println("Custom Comparator - Guava ComparisonChain");
+        sorter.sortUsingComparator_Guava_ComparisonChain();
+
+        System.out.println();
+        System.out.println("Custom Comparator - Commons CompareToBuilder");
+        sorter.sortUsingComparator_Commons_CompareToBuilder();
+
+        System.out.println();
+        System.out.println("Comparator Factory - Comparator.comparing()");
+        sorter.sortUsingComparator_Comparing();
+    }
+}
+
+@ToString
+@Getter
+@RequiredArgsConstructor
+class Student {
+    private final long id;
+    private final String name;
+    private final int age;
+}
+
+class SimpleComparator implements Comparator<Student> {
+    @Override
+    public int compare(Student o1, Student o2) {
+        int difference = o1.getName().compareTo(o2.getName());
+
+        return (difference != 0) ? difference
+                : Integer.compare(o1.getAge(), o2.getAge());
+    }
+}
+
+class GuavaBasedComparator implements Comparator<Student> {
+    @Override
+    public int compare(Student o1, Student o2) {
+        return ComparisonChain.start()
+                .compare(o1.getName(), o2.getName())
+                .compare(o1.getAge(), o2.getAge())
+                .result();
+    }
+}
+
+class ApacheCommonsBasedComparator implements Comparator<Student> {
+    @Override
+    public int compare(Student o1, Student o2) {
+        return new CompareToBuilder()
+                .append(o1.getName(), o2.getName())
+                .append(o1.getAge(), o2.getAge())
+                .build();
+    }
+}