Array of custom Java objects

Question

I am trying to create an array of Person (a class that with variables String name, and double total). But for some reason, creating a second Person replaces(?) the first person. . .

Person[] p = new Person[40];
    
p[0] = new Person("Jango", 32);
p[1] = new Person("Grace", 455);
    
System.out.println( p[0].getName() );
System.out.println( p[1].getName() );
System.out.println( p[0].equals(p[1]) );

The output is:

Grace
Grace
false

Why isn't it:

Jango
Grace
false

????????????

public class Person {

    @SuppressWarnings("unused")
    private Person next;
    private String name;
    private double total;

    public Person(String _name)
    {
        name = _name;
        total = 0.0;
        next = null;
    }

    public Person(String _name, double _total)
    {
        name = _name;
        total = _total;
        next = null;
    }

    public String getName()
    {
        return name;
    }
}

can you show us the person class? maybe you use a static variable to store the name? — Henry
– Henry, Commented Dec 21, 2012 at 21:19
Assuming a sane definition of Person, this shouldn't happen. Either you typo'd one of the array indices in your actual code, or the error is in Person. — user395760
– user395760, Commented Dec 21, 2012 at 21:20
You need to look up what "static" means in a class field, and also how object comparison works in Java. — Brian Roach
– Brian Roach, Commented Dec 21, 2012 at 21:21

Joel · Accepted Answer · 2012-12-21 21:27:23Z

6

Your problem is that the name instance variable is declared as static, making it a class variable. Any change to name will be changed for every instance of that class.. You need to remove the static identifier from name and from total and your code will work fine.

edited Dec 21, 2012 at 21:27

answered Dec 21, 2012 at 21:22

Joel

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4 Comments

Edwin Dalorzo Over a year ago

If they are static they are not instance variables. So your statement is contradictory.

Joel Over a year ago

Well, name would be an instance variable for a Person class.. and that is what he is trying to do.. That is why I used the term.

Edwin Dalorzo Over a year ago

If they are static they are class variables, not instance variables. Arent't they?

Joel Over a year ago

You are correct... And I am aware. I was trying to say that he declared instance variables as static... making them class variables. which is not what he intended to do. Sorry for not typing it all out..

Reimeus · Accepted Answer · 2012-12-21 21:30:38Z

3

Currently these variables are static which means that they they will retain the last values assigned.

private static String name;
private static double total;

You need to make these fields class instance variables:

private String name;
private double total;

See Understanding Instance and Class Members

edited Dec 21, 2012 at 21:30

answered Dec 21, 2012 at 21:22

Reimeus

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Comments

TimoteeTheCodeMonkee · Accepted Answer · 2012-12-21 21:24:29Z

1

Your fields are static. They should not be, if you want them to be able to store a separate instance of a name and total for each instance of the class.

answered Dec 21, 2012 at 21:24

TimoteeTheCodeMonkee

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