Create HashCodeAndEqualsMethod.java

rahulXbarnwal · web-flow · commit 09d90e49138a · 2026-03-15T01:52:04.000+05:30
diff --git a/src/learnCollections/HashCodeAndEqualsMethod.java b/src/learnCollections/HashCodeAndEqualsMethod.java
@@ -0,0 +1,70 @@
+package learnCollections;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+
+public class HashCodeAndEqualsMethod {
+    public static void main(String[] args) {
+        HashMap<Person, String> map = new HashMap<>();
+        Person p1 = new Person("Alice", 1);
+        Person p2 = new Person("Bob", 2);
+        Person p3 = new Person("Alice", 1); // same content as p1 but different object -> diff memory -> diff hashcode
+        
+        map.put(p1, "Engineer"); // hashcode1 --> index1
+        map.put(p2, "Designer"); // hashcode2 --> index2
+        map.put(p3, "Manager");  // hashcode3 --> index3
+
+        System.out.println("HashMap Size: " + map.size()); // 3 because p1 and p3 are different objects (different hashcodes) even though they have same content
+        System.out.println("Value for p1: " + map.get(p1)); // Engineer
+        System.out.println("Value for p3: " + map.get(p3)); // Manager
+
+        // After overriding equals() and hashCode() in Person class, p1 and p3 are considered equal (same content) and will have same hashcode, so p3 will replace p1's value in the map
+        // HashMap Size: 2
+        // Value for p1: Manager
+        // Value for p3: Manager
+
+
+        Map<String, Integer> map1 = new HashMap<>();
+        map1.put("Shubham", 90); // hashcode1 --> index1
+        map1.put("Neha", 92);    // hashcode2 --> index2
+        map1.put("Shubham", 99); // hashcode1 --> index1 --> equals() --> replace
+    }
+}
+
+class Person {
+    String name;
+    int id;
+
+    public Person(String name, int id) {
+        this.name = name;
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+
+        Person person = (Person) o;
+        return id == person.getId() && Objects.equals(name, person.getName());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(name, id);
+    }
+
+    @Override
+    public String toString() {
+        return "id: " + id + ", name: " + name;
+    }
+}
