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Question about the task

AmigoSet (part 2)

Java Collections, Level 4, Lesson 15

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Am i stupid or is this task bugged. i did everything that conditions said and still one condition doesnt validate!!!

We won't re-invent the mechanism for working with hashes — It has already been implemented in lots of collections.
We'll grab HashMap and use it.

1. Create a private Object PRESENT constant and initialize it with an Object. This will be our stub.

2. Create a private transient HashMap<E, Object> map field. A list of keys will be our set. And instead of values, we'll shove the PRESENT stub into the map.
Remember, we only need keys, and for each key we'll insert PRESENT instead of values. We've got to have something there :)
Let's see what we end up with :)
Collections usually have several constructors, so:

3. Create a no-argument constructor that initializes the map field.

4. Create a constructor with one Collection<? extends E> collection parameter.
To initialize the map field, use a constructor that lets you pass the initial capacity.
Calculate your capacity using the following formula: the maximum of 16 and the rounded-up value of (collection.size()/.75f)
Add all of the elements from the passed collection to our collection.
We have the method needed to add all the elements thanks to the fact that AbstractSet inherits AbstractCollection.

5. Write your own implementation of the add(E e) method: add element e to map as a key with PRESENT as the value.
Return true if the new element was added, otherwise return false.

Requirements:

A private static final PRESENT field must be created and initialized with an Object in the AmigoSet class.
The AmigoSet class must create a private transient HashMap map field.
The AmigoSet class must implement a no-argument constructor as outlined in the task conditions.
The AmigoSet class must implement a constructor with a single Collection parameter as outlined in the task conditions.
The add method must add a new element to map using the passed parameter as the key and the PRESENT object as the value.
The add method must return true if the new element was successfully added; otherwise, it must return false.

package com.codegym.task.task37.task3707; import java.io.Serializable; import java.util.*; import static java.lang.Math.*; public class AmigoSet<E> extends AbstractSet implements Serializable, Cloneable , Set { private static final Object PRESENT = new Object(); private transient HashMap<E,Object> map; public AmigoSet() { this.map = new HashMap<>(); } public AmigoSet(Collection<? extends E> collection) { this.map= new HashMap<>(max(16,(int) ceil(collection.size()/.75f))); for (E o : collection) map.put(o, PRESENT); } @Override public Iterator iterator() { return null; } @Override public boolean addAll(Collection c) { return false; } @Override public int size() { return 0; } @Override public boolean add(Object e){ if (map.containsKey(e)){ return false; }else{ map.put((E)e,PRESENT); return true; } } }

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Roman

Level 41

16 October 2019, 12:07

solution

Some bug detected. Change (int) ceil(collection.size()/.75f) to (int) (collection.size()/.75f + 1) we'll fix this soon