BAEL-1331: Quick Example: Comparator vs Comparable in Java Source code and Unit Tests added.

core-java/src/main/java/com/baeldung/comparable/Player.java

@@ -0,0 +1,51 @@
+package com.baeldung.comparable;
+
+public class Player implements Comparable<Player> {
+
+    private int ranking;
+
+    private String name;
+
+    private int age;
+
+    public Player(int ranking, String name, int age) {
+        this.ranking = ranking;
+        this.name = name;
+        this.age = age;
+    }
+
+    public int getRanking() {
+        return ranking;
+    }
+
+    public void setRanking(int ranking) {
+        this.ranking = ranking;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+
+    @Override
+    public String toString() {
+        return this.name;
+    }
+
+    @Override
+    public int compareTo(Player otherPlayer) {
+        return (this.getRanking() - otherPlayer.getRanking());
+    }
+
+}

core-java/src/main/java/com/baeldung/comparable/PlayerSorter.java

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+package com.baeldung.comparable;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+public class PlayerSorter {
+
+    public static void main(String[] args) {
+        
+        ArrayList<Player> footballTeam = new ArrayList<Player>();
+        Player player1 = new Player(59, "John", 20);
+        Player player2 = new Player(67, "Roger", 22);
+        Player player3 = new Player(45, "Steven", 24);
+        footballTeam.add(player1);
+        footballTeam.add(player2);
+        footballTeam.add(player3);
+        
+        System.out.println("Before Sorting : " + footballTeam);
+        Collections.sort(footballTeam);
+        System.out.println("After Sorting : " + footballTeam);
+        
+    }
+
+}

core-java/src/main/java/com/baeldung/comparator/Player.java

@@ -0,0 +1,46 @@
+package com.baeldung.comparator;
+
+public class Player {
+
+    private int ranking;
+
+    private String name;
+
+    private int age;
+
+    public Player(int ranking, String name, int age) {
+        this.ranking = ranking;
+        this.name = name;
+        this.age = age;
+    }
+
+    public int getRanking() {
+        return ranking;
+    }
+
+    public void setRanking(int ranking) {
+        this.ranking = ranking;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+
+    @Override
+    public String toString() {
+        return this.name;
+    }
+
+}

core-java/src/main/java/com/baeldung/comparator/PlayerAgeComparator.java

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+package com.baeldung.comparator;
+
+import java.util.Comparator;
+
+public class PlayerAgeComparator implements Comparator<Player> {
+
+    @Override
+    public int compare(Player firstPlayer, Player secondPlayer) {
+       return (firstPlayer.getAge() - secondPlayer.getAge());
+    }
+
+}

core-java/src/main/java/com/baeldung/comparator/PlayerAgeSorter.java

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+package com.baeldung.comparator;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+public class PlayerAgeSorter {
+
+    public static void main(String[] args) {
+        
+        ArrayList<Player> footballTeam = new ArrayList<Player>();
+        Player player1 = new Player(59, "John", 22);
+        Player player2 = new Player(67, "Roger", 20);
+        Player player3 = new Player(45, "Steven", 24);
+        footballTeam.add(player1);
+        footballTeam.add(player2);
+        footballTeam.add(player3);
+        
+        System.out.println("Before Sorting : " + footballTeam);
+        //Instance of PlayerAgeComparator
+        PlayerAgeComparator playerComparator = new PlayerAgeComparator();
+        Collections.sort(footballTeam, playerComparator);
+        System.out.println("After Sorting by age : " + footballTeam);
+        
+    }
+
+}

core-java/src/main/java/com/baeldung/comparator/PlayerRankingComparator.java

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+package com.baeldung.comparator;
+
+import java.util.Comparator;
+
+public class PlayerRankingComparator implements Comparator<Player> {
+
+    @Override
+    public int compare(Player firstPlayer, Player secondPlayer) {
+       return (firstPlayer.getRanking() - secondPlayer.getRanking());
+    }
+
+}

core-java/src/main/java/com/baeldung/comparator/PlayerRankingSorter.java

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+package com.baeldung.comparator;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+public class PlayerRankingSorter {
+
+    public static void main(String[] args) {
+        
+        ArrayList<Player> footballTeam = new ArrayList<Player>();
+        Player player1 = new Player(59, "John", 22);
+        Player player2 = new Player(67, "Roger", 20);
+        Player player3 = new Player(45, "Steven", 40);
+        footballTeam.add(player1);
+        footballTeam.add(player2);
+        footballTeam.add(player3);
+        
+        System.out.println("Before Sorting : " + footballTeam);
+        //Instance of PlayerRankingComparator
+        PlayerRankingComparator playerComparator = new PlayerRankingComparator();
+        Collections.sort(footballTeam, playerComparator);
+        System.out.println("After Sorting by ranking : " + footballTeam);
+        
+    }
+
+}

core-java/src/test/java/com/baeldung/comparable/ComparableUnitTest.java

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+package com.baeldung.comparable;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+import org.junit.Test;
+
+public class ComparableUnitTest {
+    
+    @Test
+    public void whenUsingComparable_thenSortedList() {
+        ArrayList<Player> footballTeam = new ArrayList<Player>();
+        Player player1 = new Player(59, "John", 20);
+        Player player2 = new Player(67, "Roger", 22);
+        Player player3 = new Player(45, "Steven", 24);
+        footballTeam.add(player1);
+        footballTeam.add(player2);
+        footballTeam.add(player3);
+        Collections.sort(footballTeam);
+        assertEquals(footballTeam.get(0).getName(), "Steven");
+        assertEquals(footballTeam.get(2).getRanking(), 67);
+    }
+
+}

core-java/src/test/java/com/baeldung/comparator/ComparatorUnitTest.java

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+package com.baeldung.comparator;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+import org.junit.Test;
+
+public class ComparatorUnitTest {
+    
+    @Test
+    public void whenUsingRankingComparator_thenSortedList() {
+        ArrayList<Player> footballTeam = new ArrayList<Player>();
+        Player player1 = new Player(59, "John", 20);
+        Player player2 = new Player(67, "Roger", 22);
+        Player player3 = new Player(45, "Steven", 24);
+        footballTeam.add(player1);
+        footballTeam.add(player2);
+        footballTeam.add(player3);
+        PlayerRankingComparator playerComparator = new PlayerRankingComparator();
+        Collections.sort(footballTeam, playerComparator);
+        assertEquals(footballTeam.get(0).getName(), "Steven");
+        assertEquals(footballTeam.get(2).getRanking(), 67);
+    }
+    
+    @Test
+    public void whenUsingAgeComparator_thenSortedList() {
+        ArrayList<Player> footballTeam = new ArrayList<Player>();
+        Player player1 = new Player(59, "John", 20);
+        Player player2 = new Player(67, "Roger", 22);
+        Player player3 = new Player(45, "Steven", 24);
+        footballTeam.add(player1);
+        footballTeam.add(player2);
+        footballTeam.add(player3);
+        PlayerAgeComparator playerComparator = new PlayerAgeComparator();
+        Collections.sort(footballTeam, playerComparator);
+        assertEquals(footballTeam.get(0).getName(), "John");
+        assertEquals(footballTeam.get(2).getRanking(), 45);
+    }
+
+}