How to get information from an object?

Question

I have two classes the second one looks like this:

public class personal_id{
privete int id=0;
private String name;
public personal_id(String name){
name=this.name;
id++;
}
}

And the main is

public class creator{
public static void main(String[]arg){
personal_id obj1=new personal_id("John");
personal_id obj2=new personal_id("Jane");
personal_id obj3=new personal_id("Jim");
personal_id obj4=new personal_id("Lucas");
}
}

I think I have created 4 objects. John with id 0, Jane with id 1, Jim with id 2 and Lucas with id 3. Now I want to know how can I get information from the obj3 or some other object. For example I don't know the name and the id of the object. How can I do that?

You cannot access the `private` members so easily. Either provide *getters* or change `private` to other access specifier. Are you able to modify the `personal_id` class? — Fureeish, Dec 29 '17 at 01:22
[Read more about access modifiers](https://stackoverflow.com/questions/215497/in-java-difference-between-package-private-public-protected-and-private) — Zachary, Dec 29 '17 at 01:24

acdcjunior · Accepted Answer · 2017-12-29T01:36:27.997

You have a couple of options, but the generally best approach here is to create getters:

public class PersonalId { // ------------------- renamed: it was "personal_id"
    private int id = 0;   // ------------------- fixed: was "privete" instead of "private"
    private String name;
    public PersonalId(String name) { // ------------------- renamed: it was "personal_id"
        this.name = name; // ----------------- fixed: was "name = this.name"
        id++; // this line makes little sense, it's the same as declaring id = 1;
    }

    public int getId() {      // ------------------- added
        return this.id;       // ------------------- added
    }                         // ------------------- added
    public String getName() { // ------------------- added
        return this.name;     // ------------------- added
    }                         // ------------------- added
}

And use it like:

public class Creator { //  -------------- renamed: was "creator"
    public static void main(String[] arg) {
        PersonalId john = new PersonalId("John");
        System.out.println("John's id: "+ john.getId());
        System.out.println("John's name: "+ john.getName());
    }
}

Output:

John's id: 1
John's name: John

Generally speaking, you could also change the properties' visibility from private to public (e.g. private int id = 0; to public int id = 0;) and use it like System.out.println("John's id: "+ john.id);, but that is generally frowned upon -- it is considered a bad practice since it does not foster proper object encapsulation.

Sidenotes

As you can see from the comments, your code also had some other problems.

Firstly, the name of the classes violate Java naming conventions and guidelines, in which the name of classes should be camelCase. In other words, you should have PersonalId instead of personal_id. Also, you should use Creator instead of creator (notice the first letter, it should be uppercase).

Also your constructor increments id in:

id++;

But that makes little sense, since id is declared with a starting value of 0 (private int id=0;), id's value will always be 1 after the construction.

How to get information from an object?

1 Answers1

Sidenotes