How to Modify a Key in a HashMap? (#14496)

core-java-modules/core-java-collections-maps-6/src/test/java/com/baeldung/map/changekey/HashmapChangeKeyUnitTest.java

@@ -0,0 +1,98 @@
+package com.baeldung.map.changekey;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+class Player {
+    private String name;
+
+    public Player(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (!(o instanceof Player)) {
+            return false;
+        }
+
+        Player player = (Player) o;
+
+        return name.equals(player.name);
+    }
+
+    @Override
+    public int hashCode() {
+        return name.hashCode();
+    }
+}
+
+public class HashmapChangeKeyUnitTest {
+
+    @Test
+    void whenRemoveThenPutWithTheNewKey_thenGetExpectedResult() {
+        Map<String, Integer> playerMap = new HashMap<>();
+
+        playerMap.put("Kai", 42);
+        playerMap.put("Amanda", 88);
+        playerMap.put("Tom", 200);
+
+        // now replace Kai with Eric
+        playerMap.put("Eric", playerMap.remove("Kai"));
+
+        assertFalse(playerMap.containsKey("Kai"));
+        assertTrue(playerMap.containsKey("Eric"));
+        assertEquals(42, playerMap.get("Eric"));
+    }
+
+    @Test
+    void whenChangeTheKey_thenMayNotGetExpectedResult() {
+        Map<Player, Integer> myMap = new HashMap<>();
+        Player kai = new Player("Kai");
+        Player tom = new Player("Tom");
+        Player amanda = new Player("Amanda");
+
+        myMap.put(kai, 42);
+        myMap.put(amanda, 88);
+        myMap.put(tom, 200);
+
+        assertTrue(myMap.containsKey(kai));
+
+        //change Kai's name to Eric
+        kai.setName("Eric");
+        assertEquals("Eric", kai.getName());
+
+        Player eric = new Player("Eric");
+        assertEquals(eric, kai);
+
+        // the map contains neither Kai nor Eric:
+        assertFalse(myMap.containsKey(kai));
+        assertFalse(myMap.containsKey(eric));
+
+        // although the Player("Eric") exists:
+        long ericCount = myMap.keySet()
+          .stream()
+          .filter(player -> player.getName()
+            .equals("Eric"))
+          .count();
+
+        assertEquals(1, ericCount);
+    }
+}