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If you want to access functions/variables of a class from a different class they can't be private. The modifier private means that a function/variable can only be accessed from within the same class. Try the default, protected or public modifier.
When a member (Variables, methods, and constructors) is private, it is only accessible within the same class as it is declared. Attempting to access or instantiate it from another class would throw java.lang.IllegalAccessException exception.
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java.lang.IllegalAccessException: Class com.abcdef.bus.model.service.Transaction can not access a member of class com.abcdef.bus.model.service.Customer with modifiers "private static final"