Lecture 21 Objectives

KNOW:

• That Java has a built-in hash table class (HashMap)
• How to use the HashMap methods get(), put(), and containsKey()
• The relationship between the methods equals() and hashCode()

BE ABLE TO:

• Define and use a Java HashMap
• Design the hashCode() and equals() methods for a class in a way that maintains their relationship

Sample Exam Question:

A Student class is defined as follows:

class Student{
   String name;
   int id;
   String address;

   ...
}

boolean equals(Object o){
  if ( o instanceof Student)
       return this.name.equals(((Student)o).name) &&
              this.id == ((Student)o).id;
  else
       return false;
}