JOptionPane.showMessageDialog(parent, "メッセージ");

JOptionPane.showMessageDialog(parent, "This is an error!", "Error", JOptionPane.ERROR_MESSAGE);

int ret = JOptionPane.showConfirmDialog(parent, "Are you sure to delete?",
        "Delete a memo", JOptionPane.YES_NO_OPTION);
if (ret == JOptionPane.OK_OPTION) {
    System.out.println("OK");
}

String inputValue = JOptionPane.showInputDialog("Please input a value");
if (inputValue == null || inputValue.isEmpty()) {
    return;
}
System.out.println(inputValue);

String inputValue = JOptionPane.showInputDialog("Please input a value", "default value");
if (inputValue == null || inputValue.isEmpty()) {
    return;
}
System.out.println(inputValue);