How can I change automatically a Label setter name in the program when it is running?

For example

JLabel label0 = new JLabel("");
JLabel label1 = new JLabel("");
JLabel label2 = new JLabel("");
JLabel label3 = new JLabel("");
JLabel label4 = new JLabel("");

for (int i = 0;i<5;i++)
{
    labeli.setText(i);
    
}

In this code, the for automatically change the label texts, first the label0 and after then the label1 etc.. Obviusly, this isn't working. My best solution was I do an if, and if i == 0 set label0 etc.. but maybe there is an easier solution which I don't know. (And if I make 100 elements, it is very long time to write down)

At the simplest of levels, you have a number of objects you want to maintain in an easy/accessible container. Assuming for a second that the list is of a predefined or, after it's initialisation, will never change size without needing to be be re-initialised, an array would be a good choice.

See Arrays for more details.

For example...

import java.awt.EventQueue;
import java.awt.GridLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Test {

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

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private JLabel[] labels = new JLabel[6];

        public TestPane() {
            setLayout(new GridLayout(0, 1));
            for (int index = 0; index < labels.length; index++) {
                JLabel label = new JLabel(Integer.toString(index));
                // Customise the label, as it' easy to type `label`
                // then `labels[index]` ;)
                add(label);
                labels[index] = label;
            }
        }

    }

}

If, on the other hand, you need something which is more dynamic (can grow and shrink at runtime), then a List of some kind would be more practice, but since you don't seem to understand arrays, maybe you should stick with those first.