In this post, we will learn the difference between "equals()" and "compareTo()" methods in Java. This is a frequently asked question in Java interviews for beginners. Let's dive into it.
| Feature | equals() method | compareTo() method |
|---|---|---|
| Defined in | Defined in the Object class. | Defined in the Comparable interface. |
| Method signature | public boolean equals(Object obj) | public int compareTo(T obj) |
| Purpose | Used to check if two objects are equal. | Used to compare two objects for ordering. |
| Return Type | Returns a boolean (true if objects are equal, false otherwise). | Returns an integer (negative, zero, or positive). |
| Method Parameters | Takes an Object type as a parameter, and requires casting to the specific class type for comparisons. | Takes a parameter of the same class type as the implementing class. |
| Natural Ordering | Generally overridden for specific class types to define equality based on their properties. | Generally overridden to provide natural ordering of objects. |
| Implementation | Developer-defined for custom object comparisons. | Developer-defined for custom object comparisons. |
| Relation with equals() | It's recommended to override "equals()" whenever you override "compareTo()", to ensure consistency between equality and ordering. | If "compareTo()" is not defined or inconsistent with "equals()", sorting methods may not work as expected. |
| Interface Dependency | Not required to implement any interface. | Required to implement the Comparable<T> interface. |
| Use in Collections | Used by certain collection classes like HashSet and HashMap to determine object uniqueness. | Used by collection classes like TreeSet and TreeMap to sort elements. |