very Strange behaviour !!

[selimzz]

I've faced a very strange issue in java ,no one could describe to me why does java do that !!!so i would plz to understand this issue if anyone could

I've 2 classes City and User

and City has arrayList of users

if i have in my program arraylist of City(say cities) and i want to change property in specific user object (has say 'x' index) in the arraylist of specific object of city in cities
the strange behaviour is that : the user which has index 'x' will be changed in all City objects in cities not the spicific one


Code:

for(City city:cities)
{
city.setUsers(users);
}

cities.get(0).getUsers().get(0).setCity_id(3);
System.out.println(cities.get(1).getUsers().get(0) .getCity_id());


although i wrote cities.get(1) ,it'll print 3 not 0 but if i change getUsers().get(0) to get(1) will print 0 !!!!!!!!!!!!!!!!!

[Norm]

Please make a small, complete program (paste it here) that compiles, executes and shows the problem. Run the program, copy its output and paste it here and add some comments to show what is wrong with the output and what it should be.

Be sure to wrap the code in code tags. http://www.java-forums.org/misc.php?do=bbcode#code

[JosAH]

for(City city:cities)
{
city.setUsers(users);
}

That snippet sets the same (ArrayList) of users to each city ...

kind regards,

Jos

[selimzz]

yeah i thought about it but that it isn't the problem as i set different arraylist from different objects of users to each city and it was the same result :s

[Norm]

Can you make a SSCCE for testing? Short, Self Contained, Correct Example

[DarrylBurke]

selimzz, please go through the Forum Rules -- particularly the third paragraph.

db

[JosAH]

yeah i thought about it but that it isn't the problem as i set different arraylist from different objects of users to each city and it was the same result :s

Show us some of your actual code; I'm sure it's something similar as I pointed out in my previous reply.

kind regards,

Jos

[selimzz]

Show us some of your actual code; I'm sure it's something similar as I pointed out in my previous reply.

kind regards,

Jos

here The actual Code:

import java.util.ArrayList;

	class User
	{
		private boolean activeFlag;

		public boolean isActiveFlag() {
			return activeFlag;
		}

		public void setActiveFlag(boolean activeFlag) {
			this.activeFlag = activeFlag;
		}
		
		
	}
    class City
    {
    	private String name;
    	private ArrayList<User>users;
    	public City(String name,ArrayList<User>users)
    	{
    		this.name=name;
    		this.users=users;
    	}
		public String getName() {
			return name;
		}
		public void setName(String name) {
			this.name = name;
		}
		public ArrayList<User> getUsers() {
			return users;
		}
		public void setUsers(ArrayList<User> users) {
			this.users = users;
		}
    }
	/**
	 * @param args
	 */
    public class Test {
	public static void main(String[] args) {
		
		User u1=new User();
		User u2=new User();
		User u3=new User();
		User u4=new User();
		ArrayList <User>users1=new ArrayList<User>();
		users1.add(u1);users1.add(u2);
		ArrayList <User>users2=new ArrayList<User>();
		users2.add(u3);users2.add(u4);
		City city1=new City("Tokyo",users1);
		City city2=new City("London",users2);
		ArrayList<City> cities=new ArrayList<City>();
		cities.add(city1);cities.add(city2); 
		cities.get(0).getUsers().get(0).setActiveFlag(true);
		System.out.println(cities.get(0).getUsers().get(0).isActiveFlag());//true :s!! why !!!
		System.out.println(cities.get(0).getUsers().get(1).isActiveFlag());// false as expected because of getUsers().get(1)
		

	}

}

[selimzz]

I did ,it will be in mind next time :)

[DarrylBurke]

Guide For New Members
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db

[JosAH]

		cities.get(0).getUsers().get(0).setActiveFlag(true);
		System.out.println(cities.get(0).getUsers().get(0).isActiveFlag());//true :s!! why !!!

The active flag is true becaue you have set it so the line before; nothing strange about it ...

kind regards,

Jos

[selimzz]

The active flag is true becaue you have set it so the line before; nothing strange about it ...

kind regards,

Jos

hahaha sorry i mean System.out.println(cities.get(1).getUsers().get(0) .isActiveFlag());

[JosAH]

I just ran your code and it returned false (as expected). Did you recompile your code before testing it?

kind regards,

Jos