Question

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HashMaps

A hashtable is a data structure that allows the user to look up things by a key value. Java implements a hashtable

called “HashMap”. The way it works is to specify two types of classes. One is the “key”, and another is the

“value”. You can put data values into the HashMap at an “index” specified by the key.

Like ArrayList, HashMap is a generic class, so you declare it using angle brackets. For HashMap, you must

include both the key type and the value type in this declaration, so the declaration looks like

HashMap<Key,Value>. As an example, the following declares a HashMap with a String key and an Integer

value:

HashMap<String, Integer> h = new HashMap<String, Integer>();

HashMap has quite a few useful methods. A couple of the most important are “put”, to put (key,value) pairs into

the HashMap, and “get” to get a value based on a key. For example:

h.put("Hello", 1);

int helloVal = h.get("Hello");

Other methods of HashMap clear the table, determine if a certain key or value is stored in the table, remove a value, and get a list of all keys in the table.

Q7) Suppose that your program has a HashMap called plants with keys that are Strings and values that are

Integers. What code would you use to print the value associated with the string "grass"?

Part 3) Copy and complete the following program that does a little bit with HashMap.

Part 3) Copy and complete the following program that does a little bit with HashMap. // Lab 7b // <Name> // <Section> import java.util.*; public class Lab7b public static void main(String args[]) // Create a new HashMap called "songStars" HashMap<String, Integer> songStars - // (Your code here) // Yes, you should listen to all these on Youtube. songStars.put("The ballad of Bilbo Baggins", 5); songstars.put("A still more glorious dawn", 4); songStars.put("A finite simple group of order two", 4); songStars.put("Code monkey", 4); songStars.put("Fish heads", 2); songStars.put("I'll form the head", 3); songStars.put("Honeybee", 5); songStars.put("Silver apples of the moon", 4); // Get the number of stars for "Code monkey", and print the # of stars // (Your code here) // Remove the song "Honeybee" // [Your code here) // Determine if "Honeybee" is still in the table. // If it is in the table, print "Honeybee still in table". // Otherwise print "Successfully removed Honeybee". // [Your code here] Part 4 Make sure that your code compiles and runs correctly.

Answer 1

Here is the code for the above assignment.

Feel free to comment on any doubt and give thumbs up!

Code:

import java.util.HashMap;

public class Lab7b

{

public static void main(String[] args) {

// Create a new HashMap called "songsStarts"

HashMap<String, Integer> songStars = new HashMap<>();

// Yes, you should listen to all these on Youtube

songStars.put("The balled of Bilbo Baggins", 5);

songStars.put("A still more glorious dawn", 4);

songStars.put("A finite simple group of order two", 4);

songStars.put("Code monkey", 2);

songStars.put("Fish heads", 2);

songStars.put("I;ll form the head", 3);

songStars.put("Honeybee", 5);

songStars.put("Silver apples of the moon", 4);

// Get the number of stars for "Code monkey", and print the # of stars

int numberOfStars = songStars.get("Code monkey");

System.out.println("Number of stars for the song Code monkey on Youtube are : " + numberOfStars);

// Remove the song "Honeybee"

songStars.remove("Honeybee");

// Determine if "Honeybee" is still in the table.

if(songStars.containsKey("Honeybee")){

System.out.println("Honeybee still in table");

}else{

System.out.println("Successfully removed Honeybee");

}

}

}

Screenshot

Number of stars for the song Code monkey on Youtube are : 2 Successfully removed Honeybee

Thank You!