What will happen if you try to modify an existing string in Java?

In Java, strings are immutable, meaning that once a string object is created, its value cannot be changed or modified. As a result, when you attempt to modify an existing string, rather than changing the original string, a new string object is created to reflect the new value. This behavior is consistent with Java's design principles, which ensure that strings remain constant across an application, thus enhancing both security and performance.

When you perform operations that appear to modify a string, such as using the substring() method, string concatenation, or any method that suggests mutation, Java internally generates a new string object with the resultant value, leaving the original string unchanged. Thus, the correctness of the answer revolves around recognizing the immutability of strings in Java and the principle that modifications result in new string instances rather than alterations to existing ones.