Chapter 18, Problem 10PE

Program Plan Intro

“hashCode” and equals method for “Pair”

Program plan:

Filename: “Pair.java”

This code snippet creates a class “Pair”. In the code,

• Define a class “Pair”.
  • Declare a variable “first” of type “T”.
  • Declare a variable “second” of type “S”.
  • Define the constructor “Pair ()”.
    • Set the value of “first”.
    • Set the value of “second”.
  • Define the method “getFirst()”.
    • Return the value of “first”.
  • Define the method “getSecond()”.
    • Return the value of second.
  • Define a method “equals”.
    • Define a pair “other”.
    • Return true if “first” is equal.
  • Define a method “hashCode”,
    • Set “h”.
    • Return “h”.

Filename: “HashMap.java”

This code snippet creates a class “HashMap”. In the code,

• Import the required packages.
• Define a class “HashMap”.
  • Define a hash set “set”.
  • Define the constructor “HashMap ()”.
    • Set hash set “set”.
  • Define a method “put”.
    • Define a pair “p”.
    • Call “remove()” on “p”.
    • Call “add()” on “p”.
  • Define a method “get()”.
    • Iterate a “for” loop,
    • If the “first” of “pair” equal to “key”.
      • Call the method “getSecond” using “pair” and return the value.
        • Return null value.
  • Define a method “remove()”.
    • Iterate a “for” loop,
    • If the “first” of “pair” equal to “key”.
      • Call “remove()”.
      • Call the method “getSecond” using “pair” and return the value.
        • Return null value.
  • Define a method “keySet()”.
    • Define a set “keySet”.
    • Iterate a “for” loop,
      • Call the method “add()” using “keySet”.
        • Return “keySet”.
  • Define a method “size()”.
    • Return the size.

Filename: “MapTester.java”

This code snippet creates a class “MapTester”. In the code,

• Import the required packages.
• Define a class “MapTester”.
  • Define the “main” method.
  • Define a Hash map “favoriteColors”.
  • Add values to “favoriteColors” using the method “add()”.
  • Call the method “remove()” to remove the element from “favoriteColors”.
  • Get the value “Romeo” from “favoriteColors” and print it.
  • Print the expected result.
  • Get “Juliet” from the “favoriteColors”.
  • Print the expected value.
  • Get the size of the “favoriteColors” and print on the screen.
  • Print the expected value.
  • Create a set “keys”.
  • Print the size of “keys”.
  • Print the expected result.