[map-sort-by-value] sort map by value

core-java-modules/core-java-collections-maps-7/src/test/java/com/baeldung/map/LinkedHashMapSortByValueUnitTest.java

@@ -0,0 +1,142 @@
+package com.baeldung.map;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+
+import org.junit.jupiter.api.Test;
+
+class Player {
+    private String name;
+    private Integer score = 0;
+
+    public Player(String name, Integer score) {
+        this.name = name;
+        this.score = score;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (!(o instanceof Player)) {
+            return false;
+        }
+
+        Player player = (Player) o;
+
+        if (!Objects.equals(name, player.name)) {
+            return false;
+        }
+        return Objects.equals(score, player.score);
+    }
+
+    @Override
+    public int hashCode() {
+        int result = name != null ? name.hashCode() : 0;
+        result = 31 * result + (score != null ? score.hashCode() : 0);
+        return result;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getScore() {
+        return score;
+    }
+}
+
+public class LinkedHashMapSortByValueUnitTest {
+    private static LinkedHashMap<String, Integer> MY_MAP = new LinkedHashMap();
+
+    static {
+        MY_MAP.put("key a", 4);
+        MY_MAP.put("key b", 1);
+        MY_MAP.put("key c", 3);
+        MY_MAP.put("key d", 2);
+        MY_MAP.put("key e", 5);
+    }
+
+    private static LinkedHashMap<String, Integer> EXPECTED_MY_MAP = new LinkedHashMap();
+
+    static {
+        EXPECTED_MY_MAP.put("key b", 1);
+        EXPECTED_MY_MAP.put("key d", 2);
+        EXPECTED_MY_MAP.put("key c", 3);
+        EXPECTED_MY_MAP.put("key a", 4);
+        EXPECTED_MY_MAP.put("key e", 5);
+    }
+
+    private static final LinkedHashMap<String, Player> PLAYERS = new LinkedHashMap();
+
+    static {
+        PLAYERS.put("player a", new Player("Eric", 9));
+        PLAYERS.put("player b", new Player("Kai", 7));
+        PLAYERS.put("player c", new Player("Amanda", 20));
+        PLAYERS.put("player d", new Player("Kevin", 4));
+    }
+
+    private static final LinkedHashMap<String, Player> EXPECTED_PLAYERS = new LinkedHashMap();
+
+    static {
+        EXPECTED_PLAYERS.put("player d", new Player("Kevin", 4));
+        EXPECTED_PLAYERS.put("player b", new Player("Kai", 7));
+        EXPECTED_PLAYERS.put("player a", new Player("Eric", 9));
+        EXPECTED_PLAYERS.put("player c", new Player("Amanda", 20));
+    }
+
+    @Test
+    void whenUsingCollectionSort_thenGetExpectedResult() {
+        List<Map.Entry<String, Integer>> entryList = new ArrayList<>(MY_MAP.entrySet());
+        Collections.sort(entryList, new Comparator<Map.Entry<String, Integer>>() {
+            @Override
+            public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
+                return o1.getValue()
+                  .compareTo(o2.getValue());
+            }
+        });
+
+        LinkedHashMap<String, Integer> result = new LinkedHashMap<>();
+        for (Map.Entry<String, Integer> e : entryList) {
+            result.put(e.getKey(), e.getValue());
+        }
+        assertEquals(EXPECTED_MY_MAP, result);
+    }
+
+    @Test
+    void whenUsingEntrycomparingByValueAndFillAMap_thenGetExpectedResult() {
+        LinkedHashMap<String, Integer> result = new LinkedHashMap<>();
+        MY_MAP.entrySet()
+          .stream()
+          .sorted(Map.Entry.comparingByValue())
+          .forEachOrdered(entry -> result.put(entry.getKey(), entry.getValue()));
+        assertEquals(EXPECTED_MY_MAP, result);
+    }
+
+    @Test
+    void whenUsingEntrycomparingByValueAndCollect_thenGetExpectedResult() {
+        LinkedHashMap<String, Integer> result = MY_MAP.entrySet()
+          .stream()
+          .sorted(Map.Entry.comparingByValue())
+          .collect(LinkedHashMap::new, (map, entry) -> map.put(entry.getKey(), entry.getValue()), Map::putAll);
+        assertEquals(EXPECTED_MY_MAP, result);
+    }
+
+    @Test
+    void whenUsingEntrycomparingByValueAndComparator_thenGetExpectedResult() {
+        LinkedHashMap<String, Player> result = PLAYERS.entrySet()
+          .stream()
+          .sorted(Map.Entry.comparingByValue(Comparator.comparing(Player::getScore)))
+          .collect(LinkedHashMap::new, (map, entry) -> map.put(entry.getKey(), entry.getValue()), Map::putAll);
+        assertEquals(EXPECTED_PLAYERS, result);
+    }
+
+}