Can you be sure that a string will always refer to an object from the String Pool when assigned?

No, not always. In Java, string literals declared in code are automatically placed in the String Pool — a special storage for unique strings. When assigning a string literal to a variable, the reference points to an object from the pool.

However, if a string is created dynamically, for example, using the new String("...") operator or by concatenation, it may not refer to an object from the String Pool, and a new object will be created in the heap.

To explicitly place a string in the pool, you can call the intern() method:

String s1 = new String("hello");
String s2 = s1.intern(); // s2 refers to the string from the pool

Thus, only string literals and strings explicitly interned via intern() are guaranteed to refer to objects from the String Pool.