import javax.swing.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
 
public class Main {
 
    private final JTextArea area = new JTextArea();
 
    public Main() throws IOException, InterruptedException {
        init();
    }
    private void init() throws IOException, InterruptedException {
        final String cmd[] = new String[3]; // 3 posiciones para los comandos separados
        cmd[0] = "cmd";
        cmd[1] = "/c";
        cmd[2] = "start";
 
        Process p = Runtime.getRuntime().exec(cmd); //tambien sirve new String[]{"cmd","/c","start"};
        p.waitFor();
        try(BufferedReader r = new BufferedReader(new InputStreamReader(p.getInputStream()))) {
            final StringBuilder sb = new StringBuilder();
            String data = "";
            while( (data = r.readLine() ) != null) {
                sb.append(data);
                sb.append("\n");
            }
            println(sb.toString());
            area.setText(sb.toString());
        }
        JOptionPane.showMessageDialog(null,area,"Informacion",1);
    }
    static void println(final String s) {System.out.println(s); }
    public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException, UnsupportedLookAndFeelException, InstantiationException, IllegalAccessException {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        new Main();
    }
}
 
 

Runtime.getRuntime().exec(COMANDOS); 
 

• Un array de tipo  String[]{"cmd","/c","start"};
• Un String con el comando "cmd /c start"

final String cmd[] = new String[3]; // 3 posiciones para los comandos separados
        cmd[0] = "cmd";
        cmd[1] = "/c";
        cmd[2] = "start";