To ensure that the variables creditAmount and debitAmount cannot change once assigned, the final keyword should be used.
Option B: Use the final keyword and assign its value in the class constructor.
Declaring a variable as final allows it to be assigned once.
Assigning the value in the constructor is acceptable for instance variables.
Option D: Use the final keyword and assign its value when declaring the variable.
Assigning the value at declaration ensures it cannot be changed later.
Why Not Other Options:
Option A: Using static with assignment in the constructor is invalid because static variables belong to the class, not instances.
Option C: Using static and assigning in a static initializer doesn't prevent reassignment unless final is also used.
Reference:
Final Variables:
"You can declare instance variables as final. A final variable can only be assigned a value once, either when you declare it or in the constructor."
- Apex Developer Guide: Classes, Objects, and Interfaces