Difference between == and .equals() in Java

In Java, == and .equals() are both used to compare things — but they compare different aspects of objects.

---

== (Reference Comparison)

== checks whether two references point to the exact same object in memory.

It does NOT check if the contents are equal.

Example:

String a = new String("hello");
String b = new String("hello");

System.out.println(a == b); // false

Even though both contain "hello", they are different objects in memory.

However:

String a = "hello";
String b = "hello";

System.out.println(a == b); // true

Because Java uses the String Pool, both references point to the same object.

---

.equals() (Content Comparison)

.equals() checks whether two objects are logically equal (same content).

For String, Integer, and many other classes, .equals() is overridden to compare values.

Example:

String a = new String("hello");
String b = new String("hello");

System.out.println(a.equals(b)); // true

Because the contents are the same.

---

Important Difference Summary

Feature	==	.equals()
Compares	Memory address	Object content
Works for primitives?	✅ Yes	❌ No
Works for objects?	✅ Yes	✅ Yes
Can be overridden?	❌ No	✅ Yes

---

Special Case: Primitives

For primitive types (int, double, boolean, etc.):

int x = 5;
int y = 5;

System.out.println(x == y); // true

== compares actual values.

.equals() cannot be used with primitives.

---

Important Warning (Null Safety)

String str = null;
str.equals("hello"); // ❌ NullPointerException

Safer way:

"hello".equals(str); // ✅ Safe

---

Real-World Rule of Thumb

• Use == for primitives

• Use .equals() for object value comparison

• Use == for objects only when you want to check if they are the same instance

---