Using a character array to store passwords is preferred over using a string in Java due to security concerns. Passwords are sensitive information, and using a character array offers some advantages in terms of security and minimizing the risk of exposure:

Immutability:

Strings in Java are immutable, which means once a string is created, it cannot be modified. This immutability can lead to potential security risks if passwords are stored as strings, as they could be inadvertently left in memory after usage and become accessible to attackers.

Garbage Collection:

Strings are managed by Java's garbage collector. When a string is no longer in use, it will eventually be collected and its memory freed. However, until that happens, sensitive information like passwords could remain in memory, making them vulnerable to memory-scanning attacks.

Memory Management:

With a character array, you have more control over when the data is cleared from memory. Once you're done using the password, you can explicitly overwrite the array with zeros, effectively erasing the sensitive data from memory.

Zeroing Memory:

Java's security guidelines recommend "zeroing" out the sensitive data in memory after it's no longer needed. This is easier to achieve with a character array because you can explicitly set the characters to zero.

String Interning:

Strings are subject to string interning, which means that the JVM might reuse existing string objects in memory. This could potentially expose the password to other parts of the application.

Secure Erasure:

Using a character array allows you to securely erase the password data from memory by setting each character to zero. This helps mitigate the risk of residual data remaining in memory even after the password is no longer needed.