Maybe MVP and MVVM could be useful too.

Hello! Thank you for your response, I understand your example.

class Person {
    private String name;
    private String officeAreaCode;
    private String officeNumber;

    public String getName() {
        return name;
    }
    public String getTelephoneNumber() {
        return ("(" + officeAreaCode + ") " + officeNumber);
    }
    public String getOfficeAreaCode() {
        return officeAreaCode;
    }
    public void setOfficeAreaCode(String arg) {
        officeAreaCode = arg;
    }
    public String getOfficeNumber() {
        return officeNumber;
    }
    public void setOfficeNumber(String arg) {
        officeNumber = arg;
    }
}

So in this class 

officeAreaCode

and

officeNumber

are considered temporary fields because they are used in the

getTelephoneNumber

method?