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

Understanding the Differences Between ".equals" and "=="

Your lecturer's insistence on using ".equals" instead of "==" for object comparison raises the question of their relative merits.

What's the Difference?

In Java, "==" compares object references, determining if two objects occupy the same memory location. It works well for primitive types (e.g., int, double) that store values directly in memory.

However, for non-primitive types (e.g., String, Object), "==" compares object references rather than the actual values stored within them. This can lead to incorrect or incomplete equality checks.

".equals," on the other hand, is a method redefined for custom classes to determine value-based equality. It can be overridden to specify custom logic for comparing objects.

Why is ".equals" Better?

Your lecturer prefers ".equals" because it:

• Provides Value Equality: It compares the actual values of objects rather than references.
• Allows for Customized Logic: It can be overridden to implement specific equality rules for custom objects.
• Handles Null Values Gracefully: Calling ".equals" on a null object safely returns false instead of throwing an error.

Example: Comparing String Objects

Consider the following code:

String x = "hello";
String y = new String(new char[] { 'h', 'e', 'l', 'l', 'o' });

"==" would evaluate to false because x and y are distinct objects despite containing the same string value. However, ".equals" would return true because it compares the values of the String objects.

Conclusion

While "==" is faster than ".equals" for primitive types, it should be avoided for non-primitive types in favor of ".equals." ".equals" provides more reliable and flexible value-based equality checks, ensuring that your code operates correctly regardless of object references or custom object definitions.

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