The Object Class

Remember the rule: every constructor starts out with a super() constructor. If you don't explicitly put it in, then the Java compiler automatically puts it in for you. Now look at the definition of Video:

class Video
{
  String  title;    // name of the item
  int     length;   // number of minutes
  boolean avail;    // is the video in the store?

  // constructor
  public Video( String ttl, int lngth )
  {
    title = ttl; length = lngth; avail = true; 
  }

  public String toString()
  {
    return title + ", " + length + " min. available:" + avail ;
  } 
}

According to the rule, the compiler automatically does this:

  // constructor
  public Video( String ttl, int lngth )
  {
    super();     // use the super class's constuctor
    title = ttl; length = lngth; avail = true; 
  }

This is correct. All classes have a parent class (a super class) except one. The class at the top of the Java class hierarchy is called Object. If a class definition does not specify a parent class then it automatically has Object as a parent class. The compiler automatically assumes, for example:

class Video extends Object
{
. . .
}