In Java, a character array is often preferred over a String for storing confidential information, such as passwords or sensitive data. The main reason behind this preference is the immutability and visibility of String objects.

1. Immutability: Strings in Java are immutable, meaning that once a String object is created, its value cannot be changed. When you manipulate a String object, such as appending or modifying its content, a new String object is created in memory. This behavior poses a security risk when dealing with sensitive information because it leaves behind copies of the information in memory that are not easily cleared or garbage collected.
2. Visibility: String objects in Java are stored in the string pool, which is a shared memory area. String literals and constant String objects are pooled to optimize memory usage. This pooling behavior means that if multiple references point to the same String object, the content of the String can be accessed by any of those references. This can lead to unintentional exposure of sensitive information if references to String objects are inadvertently leaked or shared.

In contrast, using a character array provides several advantages:

1. Mutability: Unlike Strings, character arrays can be modified directly. This allows sensitive information to be cleared from memory after it is used, reducing the risk of leaving confidential data exposed.
2. Control over memory: With a character array, you have more control over managing the memory used to store sensitive information. Once the information is no longer needed, you can explicitly overwrite or zero out the array elements, ensuring that the data is no longer present in memory.
3. Limited visibility: Unlike String objects stored in the shared string pool, character arrays are not automatically shared or accessible to other parts of the code. This reduces the risk of unintentional exposure of sensitive information.

It’s important to note that even when using a character array, proper care should be taken to ensure the secure handling of sensitive data, such as clearing the array after use and minimizing its exposure. Additionally, other security considerations, such as encryption, should also be employed to protect confidential information.