Confused

Question about the task

HashMap of cats

Java Syntax, Level 8, Lesson 3

Resolved

It seems so simple, yet why is this not working?

There is a Cat class with a String name.
Create a HashMap<String, Cat>.
Add 10 cats to the collection. The cat's name should be used as the key.
Display the result on the screen, each element on a new line.

Requirements:

The program should not read values from the keyboard.
In the addCatsToMap() method, declare a HashMap variable with (String, Cat) pairs and immediately initialize it.
The addCatsToMap() method should add all cats in the String[] cats array to the collection in accordance with the task conditions.
The program should display the contents of the collection on the screen, each pair on a new line and with the key and value separated by a hyphen.

package com.codegym.task.task08.task0803; import java.util.HashMap; import java.util.Map; /* HashMap of cats */ public class Solution { public static void main(String[] args) throws Exception { String[] cats = new String[]{"Tiger", "Missy", "Smokey", "Marmalade", "Oscar", "Snowball", "Boss", "Smudge", "Max", "Simba"}; HashMap<String, Cat> map = addCatsToMap(cats); for (Map.Entry<String, Cat> pair : map.entrySet()) { System.out.println(pair.getKey() + " - " + pair.getValue()); } } public static HashMap<String, Cat> addCatsToMap(String[] cats) { //write your code here HashMap<String, Cat> map = new HashMap<String, Cat>();//declare a HashMap variable and initialize it for (Map.Entry<String, Cat> pair : map.entrySet()){//add all cats to the String[] cats array by looping over String key = pair.getKey(); Cat value = pair.getValue(); map.put(key,value); } return map; } public static class Cat { String name; public Cat(String name) { this.name = name; } @Override public String toString() { return name != null ? name.toUpperCase() : null; } } }

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Onyejeme Emmanuel

Level 14

29 April 2020, 08:57

in your line 27, you are using a for loop on an empty map collection, you need to iterate through the array of cats given as argument and add it to the empty map collection as its key, then create Cat object and add it as the value. e.g. for(String catNames : cats){ map.put(catNames, new Cat(catNames)); }

Liliane Top

Level 17 , Amsterdam, Netherlands

29 April 2020, 14:36

Thanks for responding! I see now that the method parameter is a String [] which needs to be added to a new created and initialised Hashmap. But what still confuses me is how we add to the Hashmap. The bit about map.put() I understand but how does this work=> map.put(key, value); So key is the catNames and the Value is the CatNames???And why do we create new cat objects by the word new and it seems that is the Value? Could you please educate me? map.put(catNames, newCat(catNames));

Sela

Level 20 , Poland

27 June 2020, 04:28

hi, I will try. we must understand what is the input and what is the output of the method: - the input is just an Array (not a HashMap), it is a parameter of the method - the output is a HashMap. and what types it should contain is defined in it's declaration:

HashMap<String, Cat> map = new HashMap<String, Cat>()

this HashMap should contain not only String but also Cat. String and Cat are just types. we have to fill the HashMap with objects. Strings are created for us and stored into ordinary Array, but we have to create Cat objects by ourselves. this is why the keyword new came out.