How does Java string compare work, and when should you use `==` vs. `.equals()`?

General Discussions
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1

I’ve been using the == operator to compare strings in my program, but I encountered a bug. After switching to .equals(), the issue was resolved.

What is the difference between == and .equals() when comparing strings in Java? Is using == for string comparison a bad practice, and in what scenarios should each be used?

2

The key difference between == and .equals() when comparing strings in Java is what they compare:

== (Reference Comparison) → Checks if two string variables point to the same memory location.

.equals() (Value Comparison) → Checks if two strings have the same sequence of characters, regardless of memory location.

Example:

String s1 = "Hello";
String s2 = "Hello";
String s3 = new String("Hello");

System.out.println(s1 == s2);        // true (both reference the same literal in the string pool)
System.out.println(s1 == s3);        // false (s3 is a new object)
System.out.println(s1.equals(s3));   // true (same content)
3

When checking if two variables refer to the exact same object (e.g., singleton patterns or interned strings).

Example:

String a = "Java";
String b = "Java";
System.out.println(a == b);  // true (string pool optimization)

However, this only works for string literals. If you’re dealing with dynamically created strings, == can fail.

When should you use .equals()? Always use .equals() for actual string content comparison.

Example:

String a = "Java";
String b = new String("Java");
System.out.println(a.equals(b));  // true (content is the same)

.equals() ensures correctness regardless of how the string was created.