I have a doubt when inserting data in an array "vectors"

These vectors are in the main is a java desktop project.

Vectors:

double[] dato = new double[0];
double[] datoTemporal = new double[0];
String texto = "";

Insert:

    if (dato.length == 0) {
        dato = new double[1];
        dato[0] = Double.parseDouble(JOptionPane.showInputDialog("Ingrese el valor: "));

    } else if (dato.length > 0) {
        datoTemporal = new double[dato.length + 1];

        for (int i = 0; i < dato.length; i++) {
            datoTemporal[i] = dato[i];
        }

Here is where I have the question because it subtracts -1 from Temporal data and continues with the same size and printed its size before arriving here and after subtracting the -1 and the size does not change but if I remove it I get an error Someone explains to me because I get an error or that he does that -1.

        datoTemporal[datoTemporal.length - 1] = Double.parseDouble(JOptionPane.showInputDialog("Ingrese el valor: "));
        dato = new double[datoTemporal.length];

        for (int i = 0; i < datoTemporal.length; i++) {
            dato[i] = datoTemporal[i];
        }
    }

Show:

    String texto = "";
    if (dato.length >= 1) {
        texto = "Numero de registros " + dato.length + "\n\n";
        for (int i = 0; i < dato.length; i++) {
            texto += "Posicion " + i + ":  " + dato[i] + "\n";
        }
        JOptionPane.showMessageDialog(null, " " + texto, " Mostrar texto", JOptionPane.INFORMATION_MESSAGE);

    } else {
        JOptionPane.showMessageDialog(null, " " + texto, " Error texto", JOptionPane.ERROR_MESSAGE);
    }