How to add to ArrayList continuously

Question

What I am trying to achieve here is when the user selects the data in the ComboBox, it will match it to my HashMap, and add it to an ArrayList.

public class Stuffs {

Stuffs(){
    
    //Creating HashMap
    HashMap<String,String> map = new HashMap<>();
    map.put("LOTR 1", "The Fellowship of the Ring");
    map.put("LOTR 2", "The Two Towers");
    map.put("LOTR 3", "The Return of the King");
    
    //Creating frame
    JFrame f = new JFrame();
    f.setSize(500, 500);
    f.setVisible(true);
    
    //Creating combobox
    String choices[] = {"LOTR 1","LOTR 2","LOTR 3"};
    JComboBox cb = new JComboBox(choices);
    cb.setBounds(50, 50,90,20);
    f.setLayout(null);    
    f.setSize(300,300);
    f.add(cb);

    //Creating button
    JButton btn = new JButton("OK");
    btn.setBounds(100,100,70,20); 
    f.add(btn);
    
    
    //Get selected item from HashMap and add into arraylist
    btn.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
        
        ArrayList test = new ArrayList<>();
        String x = (String) cb.getSelectedItem();
        String y = map.get(x);
        Collections.addAll(test, x, y);
        System.out.println(test);
        }
    });
    
}

public static void main(String[] args) {
    
    new Stuffs();     
}      
    }

The code works. The output is:

[LOTR 1, The Fellowship of the Ring] 

(User selected LOTR 1 from the ComboBox)

But when I click on the button again, the ArrayList resets. What I want is so that the ArrayList keeps on adding data without replacing the initial ones, even if its repetitive. For example:

[LOTR 1, The Fellowship of the Ring, LOTR 2, The Two Towers]

Basically the user can select from the ComboBox countless of times, and the ArrayList keeps adding up and adding up.

Answer 1

As currently written, your locally declared ArrayList is being discarded (headed for garbage collection) each time the flow of control exits your action listener.

Move the list declaration outside that method, to be a member field. (As commented .)

And generally best to declare the more general type, a List rather than ArrayList . (See this Question .)

And use Java Generics rather than raw types. Add < String > .

public class Stuffs {
    // Member fields
    List < String > test = new ArrayList<>();

    // Constructor
    Stuffs(){ … }
}

As a member field of the Stuffs class, the list stays around for as long as the instance object of Stuffs lives.

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Be aware of thread-safety . As currently written, the ArrayList should only be accessed from the user-interface thread. If any other threads will access the list, you'll need to take steps to protect that resource in a thread-safe manner.