toString，

toString，

class WaterSource
{
 private String s;
 WaterSource()
 {
  System.out.println("WaterSource()");
  s = "Constructed ";
 }
 public String toString()
 {
  return s;
 }
}

public class SprinklerSystem
{
 private String valve1,valve2,valve3,valve4;
 private WaterSource source = new WaterSource();
 private int i;
 private float f;
 public String toString()
 {
  return
   "valve1 ="+ valve1 + " "+
   "valve2 ="+ valve2 + " "+
   "valve3 ="+ valve3 + " "+
   "valve4 ="+ valve4 + "/n"+
   "i= "+ i + " "+ "f=" + f + " "+
   "source =" +source;
 }
 public static void main(String args[])
 {
  SprinklerSystem sprinklers = new SprinklerSystem();
  System.out.println(sprinklers);
 }
}

在source =" +source;中  由于系统只能将string和string连接  所以此时会调用toString方法