Big Java Late Objects
Big Java Late Objects
2nd Edition
ISBN: 9781119330455
Author: Horstmann
Publisher: WILEY
Question
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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.

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