Java Adding string to a string array

Question

Hello I have been trying to add a String to a String[]. Here is what I have,

static String[] ipList = {"127.0.0.1", "173.57.51.111", "69.696.69.69"};
@Override
public void actionPerformed(ActionEvent e) {
    String newIpGet = textfield.getText();
    try {
        for ( int  i = 0; i < Main.ipList.length; i++){
            Main.ipList[i+1] = newIpGet.toString(); // <---- *****
            Main.write(Main.ipList[i]);
        }
    } catch (IOException e1) {
        e1.printStackTrace();
    }

    Main.amountOfIps = Main.amountOfIps + 1;

    System.out.println("Text Entered!");
    System.out.println("There are now " +Main.ipList.length + " Ips.");
    textfield.setVisible(false);

    label.setVisible(true);;
}

But, I keep getting java.lang.ArrayIndexOutOfBoundsException because it wont let me make any new Strings. I can't modify my declaration of ipList[] without a lot of modifications, what can I do?

Arrays have a fixed size. You either need to create a new array at the new size and copy everything over to it or use an `ArrayList`, which essentially does this — MadProgrammer, Nov 28 '15 at 05:25

Elliott Frisch · Accepted Answer · 2015-11-29T07:52:22.707

10

Java arrays are of a fixed length (JLS-10.3. Array Creation says, in part, the array's length is available as a final instance variable length). But you can use Arrays.copyOf(T[], int) to copy the array and make it one longer. As an example, something like,

String[] ipList = { "127.0.0.1" };
System.out.println(Arrays.toString(ipList));
int len = ipList.length;
ipList = Arrays.copyOf(ipList, len + 1);
ipList[len] = "192.168.2.1";
System.out.println(Arrays.toString(ipList));

Output is

[127.0.0.1]
[127.0.0.1, 192.168.2.1]

edited Nov 29 '15 at 07:52

answered Nov 28 '15 at 05:25

Elliott Frisch

198,278
20
158
249

2

Another good option. 1+ – Hovercraft Full Of Eels Nov 28 '15 at 05:27
Thanks that solved my problem! Do you happen to know how to only capture only 1 enter from acntionPerformed? It keeps duplicating it multiple times? – randomnessthatsfunny Nov 28 '15 at 05:37
Remove the loop. You only want to add it once. – Elliott Frisch Nov 28 '15 at 05:45

score 7 · Answer 2 · answered Nov 28 '15 at 05:26

What do you think will happen here:

for ( int  i = 0; i < Main.ipList.length; i++){
    Main.ipList[i+1] = newIpGet.toString();
    Main.write(Main.ipList[i]);
}

when i == Main.ipList.length - 1, and you try to access Main.ipList[i + 1] which equals Main.ipList[Main.ipList.length]? This is guaranteed to throw the exception that you're seeing.

You state:

"I cant really change my declaring of ipList[] or it would mess up my whole project."

Sometimes there are times when you just have to take the plunge and mess everything up, and this looks to be one of them. If you need an expandable array, don't use an array, but rather an ArrayList<String>.

score 0 · Answer 3 · answered Nov 28 '15 at 17:35

0

You also just could use an ArrayList<String> from the java.util package! These are of variable length and therefore not immuatable in length like an String[] is. Furthermore they do it "on the fly" when you add or remove something.

answered Nov 28 '15 at 17:35

ToxiCore

159
1
11

Java Adding string to a string array

3 Answers3