ArrayList

[carstenht]

Hi
Im having trouble getting this arraylist code working...

Have 2 classes, a person class and a main class.

Person.java

/*
 * Person.java
 *
 * Created on September 16, 2007, 8:28 AM
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 */

package javaapplication1;

/**
 *
 * @author carsten
 */
public class Person {
    private String name;
    private int alder;
    
    /** Creates a new instance of Person */
   // Empty constructor
    public Person() 
    {
        name = "<ukendt>";
        alder = 0;
        
    }
    
    // Specific constructor
    
    public Person(String newName, int newAge)
    {
        name = newName;
        alder = newAge;
                
    }
    
    /**
     *get & set methods
     */
    
    public String getName()
    {
        return name;
    }
    
    public int getAlder()
    {
        return alder;
    }
    
    public void setName(String newName)
    {
        name = newName;
    }
    
    public void setAlder(int newAlder)
    {
        alder = newAlder;
    }
    
}

Main.java

package javaapplication1;
/*
 * Main.java
 *
 * Created on September 16, 2007, 8:27 AM
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 */
import java.util.ArrayList;


/**
 *
 * @author carsten
 */
public class Main {
    
    // Create new person
    private static Person newPerson;
    private static ArrayList<Person> person;
    /** Creates a new instance of Main */
    public Main() {
        
    }
    
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        
        newPerson = new Person();
        
        person = new ArrayList<Person>();
     
        // add persons
                
        addPerson("Carsten Thomsen", 24);
        addPerson("Maria Pedersen" ,21);
      
         // print persons
        printInfo();
    }
    
    public static void addPerson(String pName, int pAlder)
    {
        
        newPerson.setName(pName);
        newPerson.setAlder(pAlder);
        
        person.add(newPerson);
     
    }
    
    public static void printInfo()
    {
        for(Person p : person)
        {
            System.out.println("Info: " + p.getName() + ", " + p.getAlder());
        }
        
    }
}

the printInfo() method prints
Info: Maria Pedersen, 21
Info: Maria Pedersen, 21

instead of in the order i added. The error must be in the add but can figure it out.

Thx in advance

[ComputerJy]

What you are doing wrong, is that you add the reference (Objects in java are references) to the arraylist then you add the same reference again.

When printing, the object only has it's latest values.

To correct that do something like:

public class Main{

     // Create new person
    private static ArrayList<Person> person;
    /** Creates a new instance of Main */
    public Main() {
        
    }
    
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        
        person = new ArrayList<Person>();
     
        // add persons
                
        addPerson("Carsten Thomsen", 24);
        addPerson("Maria Pedersen" ,21);
      
         // print persons
        printInfo();
    }
    
    public static void addPerson(String pName, int pAlder)
    {
        Person newPerson=new Person();
        newPerson.setName(pName);
        newPerson.setAlder(pAlder);
        
        person.add(newPerson);
     
    }
    
    public static void printInfo()
    {
        for(Person p : person)
        {
            System.out.println("Info: " + p.getName() + ", " + p.getAlder());
        }
        
    }
}

[carstenht]

Thanks it worked obvious mistake