How to pass arraylist in methods?

[Sandeep Kumar B]

So, here is my program which is not giving me expected output.
Can someone please explain?

Class file

package passArrayList;

//import javax.xml.bind.annotation.XmlAttribute;
//import javax.xml.bind.annotation.XmlElement;


public class Salary
{
	int id;
	int basic;
	int federaltax;
	int statetax;
	int allowance;
	public int getId() {
		return id;
	}
	
	//@XmlAttribute
	public void setId(int id) {
		this.id = id;
	}
	public int getBasic() {
		return basic;
	}
	
	//@XmlElement
	public void setBasic(int basic) {
		this.basic = basic;
	}
	public int getFederaltax() {
		return federaltax;
	}
	
	//@XmlElement
	public void setFederaltax(int federaltax) {
		this.federaltax = federaltax;
	}
	public int getStatetax() {
		return statetax;
	}
	
	//@XmlElement
	public void setStatetax(int statetax) {
		this.statetax = statetax;
	}
	public int getAllowance() {
		return allowance;
	}
	
	//@XmlElement
	public void setAllowance(int allowance) {
		this.allowance = allowance;
	}
	public String toString()
	{
		return "ID: "+getId() + " Federal: " +getFederaltax();
	}
}

Test class

package passArrayList;

import java.util.ArrayList;
import java.util.List;

public class testSalaryPopulation 
{

	public static void main(String[] args)
	{
		  List<Salary> listSalary = new ArrayList<Salary>();		  
		  listSalary = populateListSalary();	  
		  System.out.println("Size of list after additions in main method: " + listSalary .size());		  
	}
	
	public static List<Salary> populateListSalary()
	{
		Salary sal = new Salary();
		
		List<Salary> l= new ArrayList<Salary>();
		//l=lstSalary;
		//sal=lstSalary;
		for(int i=5000;i<5020;i++)
		{
			sal.setAllowance(i-4890);
			sal.setBasic(i);
			sal.setFederaltax(i-4000);
			sal.setId(i-4999);
			sal.setStatetax(i-4600);
			System.out.println(sal);
			l.add(sal);
		}
		System.out.println("Size of list after additions: " +			l.size());
		
		  for(Salary sal1:l)
		  {
			  System.out.println(sal1);
		  }		
		return l;		
	}	
}

Output is

ID: 1 Federal: 1000
ID: 2 Federal: 1001
ID: 3 Federal: 1002
ID: 4 Federal: 1003
ID: 5 Federal: 1004
ID: 6 Federal: 1005
ID: 7 Federal: 1006
ID: 8 Federal: 1007
ID: 9 Federal: 1008
ID: 10 Federal: 1009
ID: 11 Federal: 1010
ID: 12 Federal: 1011
ID: 13 Federal: 1012
ID: 14 Federal: 1013
ID: 15 Federal: 1014
ID: 16 Federal: 1015
ID: 17 Federal: 1016
ID: 18 Federal: 1017
ID: 19 Federal: 1018
ID: 20 Federal: 1019
Size of list after additions: 20
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
ID: 20 Federal: 1019
Size of list after additions in main method: 20

I was expecting to get modified list with ID's as 1,2,3, etc in main method but its not happening
Any idea why?

[John Vorwald]

You only made one object, and then added it 20 times, and kept changing the values in the one object. When you print it, you get the last values set. You need to create new objects in the loop.

either

for(int i=5000;i<5020;i++)   {  
Salary sal = new Salary();
            sal.setAllowance(i-4890);  
            sal.setBasic(i);  
            sal.setFederaltax(i-4000);  
            sal.setId(i-4999);  
            sal.setStatetax(i-4600);  
            System.out.println(sal);  
            l.add(sal);  
        }

or

Salary sal = new Salary();
for(int i=5000;i<5020;i++)   {  
            sal.setAllowance(i-4890);  
            sal.setBasic(i);  
            sal.setFederaltax(i-4000);  
            sal.setId(i-4999);  
            sal.setStatetax(i-4600);  
            System.out.println(sal);  
            l.add(new Salary(sal));  
        }

For the 2nd option, you could make a copy constructor method.