Kolekcje ArrayList?

import java.util.ArrayList;
import javax.swing.JOptionPane;
 
public class zadanie_1 {
	public static void main (String[] args){
 
		ArrayList<String> dane = new ArrayList<String>();
 
        while(true){
        	String podaje = JOptionPane.showInputDialog("Podaj dane.");
            dane.add(podaje);
            if(podaje.equals("concat")){
            	for(String b : dane){
            		System.out.print(b + " ");
            	}
            	break;
            } else if(podaje.equals(null)){
            	System.out.println("Nie podano nic");
            	break;
            }
        }
        System.out.println();
        for(String s : dane){
        	System.out.print(s + " ");
        }
	}
}

import java.util.ArrayList;
import javax.swing.JOptionPane;
 
public class zadanie_1 {
	public static void main (String[] args){
 
		ArrayList<String> dane = new ArrayList<String>();
		Double suma = 0.0;
		
        while(true){
        	String podaje = JOptionPane.showInputDialog("Podaj dane.");
            dane.add(podaje);
            if(podaje.equals("sum")){
            	for(String a : dane){
            		suma += Double.parseDouble(a);
                	System.out.println(suma + " ");
            	}
            } else if(podaje.equals("concat")){
            	for(String b : dane){
            		dane.set(dane.size()-1, " ");
            		System.out.print(b + " ");
            	}      	
            } else if(podaje.equals("end")){
            	System.out.println("Zakończno podawanie");
            	break;
            }
        }
        
        System.out.println();
        for(String s : dane){
        	System.out.print(s + " ");
        }
    }
}

if(podaje.equals("sum")){
     suma = 0.0; //tego brakowało
     for(String a : dane){
         try
         {
               suma += Double.parseDouble(a);
         }
         catch(NumberFormatException e)
         {
         }
                        
    }
    System.out.println(suma + " "); //było w złym miejscu
}

package t214006;

import java.util.ArrayList;

/**
 * Created with IntelliJ IDEA.
 * User: koziolek
 * Date: 22.03.13
 * Time: 20:37
 * To change this template use File | Settings | File Templates.
 */
public class App {

	public static void main(String args[]) {
		ArrayList<UserInput<?>> inputs = new ArrayList<UserInput<?>>();
		//... tutaj kod wczytujący dane od użytkownika przykladowo już po parsowaniu:
		inputs.add(new IntegerUserInput(1));
		inputs.add(new IntegerUserInput(1));
		inputs.add(new StringUserInput("1"));
		inputs.add(new StringUserInput("1"));
		// sobie user wywoluje concate
		applyVisitorLogic(inputs, new StringVisitor());
		// a teraz dla sum
		applyVisitorLogic(inputs, new IntegerVisitor());
	}

	private static void applyVisitorLogic(ArrayList<UserInput<?>> inputs, Visitor<?> iv) {
		for (UserInput<?> ui : inputs) {
			ui.apply(iv);
		}
		System.out.println(iv.effects());
	}


	static boolean isNumber(String s) {
		try {
			Integer.parseInt(s);
			return true;
		} catch (NumberFormatException nfe) {
			return false;
		}
	}
}


abstract class UserInput<T> {
	private T input;

	protected UserInput(T input) {
		this.input = input;
	}

	public void apply(Visitor v) {
		if (v.isAcceptable(input.getClass()))
			v.makeMyDay(input);
	}
}

class IntegerUserInput extends UserInput<Integer> {

	protected IntegerUserInput(Integer input) {
		super(input);
	}
}

class StringUserInput extends UserInput<String> {
	protected StringUserInput(String input) {
		super(input);
	}
}

interface Visitor<T> {

	boolean isAcceptable(Class<?> clazz);

	void makeMyDay(T input);

	T effects();
}

class IntegerVisitor implements Visitor<Integer> {

	Integer sum = 0;

	@Override
	public boolean isAcceptable(Class<?> clazz) {
		return Integer.class.equals(clazz);
	}

	@Override
	public void makeMyDay(Integer input) {
		sum += input;
	}

	@Override
	public Integer effects() {
		return sum;
	}

}

class StringVisitor implements Visitor<String> {

	private StringBuilder stringBuilder = new StringBuilder();

	@Override
	public boolean isAcceptable(Class<?> clazz) {
		return String.class.equals(clazz);
	}

	@Override
	public void makeMyDay(String input) {
		stringBuilder.append(input).append(" ");
	}

	@Override
	public String effects() {
		return stringBuilder.toString();
	}
}

        	ArrayList<String> napisy = new ArrayList<>();
        	float sum = 0.0f;
        	String input = null;
        	final String sumString = "sum";
        	final String endString = "end";
        	final String concatString = "concat";
        			
        	
        	while(!endString.equals(input)) {
        		input = JOptionPane.showInputDialog("Podaj dane:");
        		if (input == null) {
					continue;
				} 
        		try {
					float f = Float.parseFloat(input);
					sum += f;
					continue;
				} catch (NumberFormatException e) {
				}
        		
        		if (sumString.equals(input)) {
        			System.out.println(sum);
        			sum = 0.0f;
        		} else if (concatString.equals(input)) {
        			StringBuilder builder = new StringBuilder();
        			for (String s : napisy) {
        				builder.append(s);
        				builder.append(" ");
        			}
        			System.out.println(builder.toString());
        		} else {
        			napisy.add(input);
        		}
        	} 

import java.util.ArrayList;
import javax.swing.JOptionPane;
 
public class Zadanie_1 
{
    public static void main (String[] args)
    {
        ArrayList<String> dane = new ArrayList<String>();
        boolean done = false; 
        while(!done)
        {
            String input = JOptionPane.showInputDialog("Podaj dane:");
            if(input == null)
            {
                done = true;
            }
            else
            {
                dane.add(input);
                if(input.equals("sum") || input.equals("both"))
                {
                    double suma = 0.0;
                    for(String a: dane)
                    {
                        try
                        {
                            suma += Double.parseDouble(a);
                        }
                        catch(NumberFormatException e)
                        {
                        }                        
                    }
                    System.out.println(suma + " ");
                    done = true;
                }
                if(input.equals("concat") || input.equals("both"))
                {
                    for(String a: dane)
                    {
                        System.out.print(a + " ");
                    }
                    done = true;
                }      
            }
        }
        for(String a: dane)
        {
            System.out.println(a);
        }
    }
}