equals, ==, and compareTo for Strings

A String variable doesn't hold text directly. It holds a reference, the address of an object sitting on the heap. == checks whether two references point at the exact same object. equals opens up both objects and checks whether their characters match, position by position. Two strings can look identical on screen and still fail == if they live at different addresses — they're equal in content but not identical in identity.

This is why new String("hi") is dangerous. Writing new always builds a fresh object on the heap, even if an identical string already exists somewhere. So a brand new object and some other "hi" will never share an address, and == reports false, even though the characters match and equals reports true. String literals behave differently: Java pools them, so two literals with the same text often share one object, making == accidentally return true. That coincidence is the trap.

compareTo settles order, not just equality. It walks both strings character by character, comparing character codes, and stops at the first difference, returning a positive number, a negative number, or zero based on that difference. "apple".compareTo("banana") is negative because 'a' comes before 'b'. This connects to the bigger theme of the unit: Strings are objects living on the heap, so comparing them correctly means understanding references and calling methods, not just writing simple symbols.