从一个 class 返回到另一个 class 的方法

Question

I'm currently learning OOP in Java, I have tried to write a mini database system, everything works well but I have two methods which are located in class CivilStatus that are not working well and they keep giving me 0 as a return, the methods are PersonAge(String NationalId) and CountSingle() . I would be grateful if anyone would have solved this bug for me.

public class Person101 {
    String nationalIdString;
    String nameString;
    int Age;
    Boolean marriedBoolean;

    Person101(String newId, String name, Boolean newMarried) {
        nationalIdString = newId;
        nameString = name;
        marriedBoolean = newMarried;
        Age = 0;

    }

    public String getId() {

        return nationalIdString;
    }

    public String getName() {

        return nameString;
    }

    public int getAge() {

        return Age;
    }

    public Boolean getMarriedStatus() {

        return marriedBoolean;
    }

    public void setAge(int newAge) {
        Age = newAge;

    }

    public void setName(String newName) {
        nameString = newName;

    }

    public void print() {
        System.out.println("The name is: " + nameString + " ,Id is: " + nationalIdString);

    }

    public boolean SingleJordanian() {
        if ((nationalIdString.contains("Jor")) && (marriedBoolean == false)) {
            return true;
        } else {
            return false;
        }

    }
public void birthday() {
        Age++;
    }

}

import java.util.ArrayList;

public class CivilStatus1 {
    String nameString;
    ArrayList<Person101> personsArrayList;

    CivilStatus1(String newName) {
        nameString = newName;
        personsArrayList = new ArrayList<Person101>();

    }

    public String getName() {

        return nameString;
    }

    public ArrayList<Person101> getPerson101s() {

        return personsArrayList;
    }

    public int PersonAge(String NationalId) {
        int newAge = 0;
        for (Person101 person101 : personsArrayList) {
            if (person101.nationalIdString.equals(NationalId)) {
                newAge = person101.Age;

            } else {

            }
        }
        return newAge;

    }

    public int CountSingle() {
        int counter = 0;
        for (Person101 person101 : personsArrayList) {
            if (person101.SingleJordanian()) {
                counter = counter + 1;

            } else {

            }
        }
        return counter;
    }
}

Thanks in advance!

Answer 1

There are a few things that could be causing issues.

Firstly with the variables of each class it is better practice to specify if they are public

public String nationalIdString;
public String nameString;
public int Age;
public Boolean marriedBoolean;

or private.

private String nationalIdString;
private String nameString;
private int Age;
private Boolean marriedBoolean;

Otherwise the variables are package protected which may causing issues with accessing the variables. If you set them to private you can access them using getter methods

public String getNationalIdString(){
    return nationalIdString;
}

If you are using getters your method should look something like this

    public int PersonAge(String NationalId) {
    int newAge = 0;
    for (Person101 person101 : personsArrayList) {
        if (person101.getNationalIdString().equals(NationalId)) {
            newAge = person101.getAge();

        } else {

        }
    }
    return newAge;

}

I'm not sure if this is causing the problem but it may be. The other suggestion is using boolean instead of Boolean unless there is a specific reason why you are using it.

To help debug your code I suggest doing something like this

    public int PersonAge(String NationalId) {
    int newAge = 0;
    for (Person101 person101 : personsArrayList) {
        System.out.println("Looking for: " + NationalID + " current person: " + person101.NationalID);
        if (person101.nationalIdString.equals(NationalId)) {
            newAge = person101.Age;
        }
    }
    return newAge;

}

This should help you locate the problem, you can also add the person's name so you can compare that to the data you inputted. I also removed the else branch of the if statement as it was not used.

Also check that SingleJordanian() is working as expected as that may be root of CountSingle() not working as intended.

Answer 2

The problem is the same for both methods. Writing

personsArrayList = new ArrayList<Person101>();

creates an ArrayList , but it's empty, as you have not added any items to it. Then, when you try looping over the ArrayList

for (Person101 person101 : personsArrayList) {
    if (person101.nationalIdString.equals(NationalId)) {
        newAge = person101.Age;

    } else {

    }
}

It doesn't even enter the loop, as there is nothing to loop over.

You should first add some items to the loop, for instance:

Person101 person1 = new Person101();
personsArrayList.add(person1);

As an aside, I would suggest that you shouldn't include the variable types in the name, eg personsArrayList , marriedBoolean . You already specified the type when you declared it

ArrayList<Person101> personsArrayList;

Rather just name them persons, married etc.

Just my 2 cents:).