below content is taken from Best practice: Writing efficient code but i didn't understand why

private static String x = "example";

faster than

private static final String x ="example";

Can anybody explain this.

Using static variables for Strings

When you define static fields (also called class fields) of type String, you can increase application speed by using static variables (not final) instead of constants (final). The opposite is true for primitive data types, such as int.

For example, you might create a String object as follows:

private static final String x = "example";

For this static constant (denoted by the final keyword), each time that you use the constant, a temporary String instance is created. The compiler eliminates "x" and replaces it with the string "example" in the bytecode, so that the BlackBerry® Java® Virtual Machine performs a hash table lookup each time that you reference "x".

In contrast, for a static variable (no final keyword), the String is created once. The BlackBerry JVM performs the hash table lookup only when it initializes "x", so access is faster.

private static String x = "example";

You can use public constants (that is, final fields), but you must mark variables as private.