java - Methods lacking return types and no void? -

this piece of code in textbook, i'm not understanding method testpanels(). has no return type , no void. how can happen?

public class testpanels extends jframe {  public testpanels() {      jpanel p1 = new jpanel();     p1.setlayout(new gridlayout(4,3));      (int = 1; <= 9; i++) {         p1.add(new jbutton(""+i));     }      p1.add(new jbutton(""+0));     p1.add(new jbutton("start"));     p1.add(new jbutton("stop"));      jpanel p2 = new jpanel(new borderlayout());     p2.add(new jtextfield("time displayed here"), borderlayout.north);     p2.add(p1, borderlayout.center);      add(p2, borderlayout.east);     add(new jbutton("food placed here"), borderlayout.west);   }  public static void main(string[] args) {     testpanels frame = new testpanels();     frame.settitle("the front view of microwave oven");     frame.setsize(400, 250);     frame.setlocationrelativeto(null);     frame.setdefaultcloseoperation(jframe.exit_on_close);     frame.setvisible(true);  } } 

it constructor , not method. methods have return-type or void (no return value).