Adding to an ArrayList using input from GUI

Question

I first created an arraylist in another part of the program, then used for loops to put it in the text area. Now, I want to take input from the text field, add that to the arraylist, and display the entire array, including the new element added. I tried using a for loop again, but when i click "add" while running, the program just freezes and nothing happens. Any suggestions? Thanks.

private void btnDisplayActionPerformed(java.awt.event.ActionEvent evt) {                                           
    // Using a for loop to display unsorted list, sorting the list, then using a for loop again to display the sorted list 

    String strUnsortedList = "";
    for(int i = 0; i < strCDNames.size(); i++)  {
         strUnsortedList += strCDNames.get(i) + "\n";

    }

    Collections.sort(strCDNames);

    String strSortedList = "";
    for(int i = 0; i < strCDNames.size(); i++)  {
         strSortedList += strCDNames.get(i) + "\n";

    }
    txtOutput.setText("Unsorted Order: \n" + strUnsortedList + "\nSorted Order: \n" + strSortedList);



}                                          

private void btnAddActionPerformed(java.awt.event.ActionEvent evt) {                                       
    String strAddedList = "";
    for (int i = 0; i < strCDNames.size(); i++)  {
          strAddedList += strCDNames.add(txtInputTitleArtist.getText());
    }
    txtOutput.setText(" " + strAddedList);
}

i wil always be less than strCDNames

Vivin
– Vivin

2015-07-20 20:07:22 +00:00
Commented Jul 20, 2015 at 20:07 — Vivin
– Vivin, Commented Jul 20, 2015 at 20:07

Vivin Paliath · Accepted Answer · 2015-07-20 20:05:24Z

2

for (int i = 0; i < strCDNames.size(); i++)  {
    strAddedList += strCDNames.add(txtInputTitleArtist.getText());
}

This is an infinite loop. You keep adding to the list, which means that the list size will keep increasing. Hence i will always be lesser than strCDNames.size().

Instead you can do something like this:

strCDNames.add(txtInputTitleArtist.getText());
String strAddedList = String.join(" ", strCDNames);

answered Jul 20, 2015 at 20:05

Vivin Paliath

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Comments

alexgbelov · Accepted Answer · 2015-07-20 20:15:16Z

0

Vivin is right. I just want to add that the arraylist add method returns a boolean (https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#add-E-). So, in this case strAddedList wouldn't even be properly updated.

answered Jul 20, 2015 at 20:15

alexgbelov

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