When Should I Use `.equals()` Instead of `==` in Java?

Understanding the Difference between ".equals" and "=="

Your lecturer's instruction to use .equals instead of == in Java raises an important distinction between reference equality and value equality.

Reference Equality (==)

The == operator compares the references associated with two objects. It checks if both objects refer to the same memory location. This is applicable to non-primitive types (such as String, Integer, etc.), where each object has a unique reference.

Example:

Integer o1 = 10;
Integer o2 = 10;
System.out.println(o1 == o2); // false

Even though o1 and o2 hold the same value, they are not the same object in memory. Therefore, == returns false.

Value Equality (.equals)

The .equals method, on the other hand, allows you to compare the values of objects. It checks if two objects have the same content, regardless of their references.

Example:

String x = "hello";
String y = new String("hello");
System.out.println(x.equals(y)); // true

Here, x and y are different objects but have the same value. .equals compares their values and returns true.

Overriding .equals Method:

Additionally, .equals can be overridden in custom classes, enabling you to define your own logic for value comparison. This allows you to customize the equality behavior for specific types.

Why .equals is Preferred:

Using .equals is generally preferred over == for the following reasons:

• It ensures value equality, regardless of object identity.
• It allows custom comparison logic through overrides.
• It helps prevent potential null pointer exceptions when both objects might be null.

In your lecturer's example, .equals is recommended to compare two integer objects because it ensures that the objects have the same value, even if they refer to different memory locations.

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