Setter 和 Getter

Question

So I was trying to make a Ride system just similar to that of uber. So I was trying to set some rules regarding the registration number of the car.

public void setRegNo(String regNo) {
        if (regNo.length() == 6) {
            if (regNo.substring(0, 3).matches("[a-zA-Z]+")) {
                if (regNo.substring(3).matches("[0-9]+")) {
                    this.regNo = regNo;
                } else {
                    this.regNo = "Error! The Registration number ends with 3 numerical characters.";
                }
            } else {
                this.regNo = "Error! The registration number begins with 3 alphabetical characters.";
            }
        } else {
            this.regNo = "Error! The Registration number must be 6 characters long.";
        }
    }

According to this setter method, the registration number must be at least 6 characters long, the first three characters must be letters and the last three characters must be integers. Then I made a getter method and finally passed this registration number into a constructor of car class. But surprisingly when I am trying to print the registration number it is not obeying these rules. I have added a picture of the result which I am getting. enter image description here

So if anyone knows why is this happening please let me know.

Answer 1

You need delete from constructor parameter regNo and set this parameter using setter. Something like this:

Car car = new Car("cat", "dog", "pranav Khurana", 4);
car.setRegNo("abc3");

Another way - you can use your setter in constructor for example:

public Car(String regNo, String name) {
    this.setRegNo(regNo);
    this.name = name;
}

Answer 2

The problem is that you don't use the setter method you have implemented to set regNo of your car. You should use that setter method in your constructor method to reuse the code you have written. One other thing is that you should use regexes to check that it is in the form you want or not. Fallowing regex checks if the first three chars are "word character" and the next three are numbers:

public void setRegNo(String regNo) {
    String myRegex="\\w\\w\\w\\d\\d\\d";
    if (regNo.matches(myRegex))
        this.regNo=regNo;
    else
        System.err.println("This is not a  registration number!!!")
}