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PO(Java) When using Maps, does it make sense for a key and value to have the same type?
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copied!<p>To give a simple example, consider a <code>Place</code> class:</p> <pre><code>public class Place { //fields private String name; private String state; private int population; private int squareMileage; private int elevation; //constructors public Place() { } public Place(String name, String state) { this.name = name; this.state = state; } public Place(String name, String state, int population, int squareMileage, int elevation) { this.name = name; this.state = state; this.population = population; this.squareMileage = squareMileage; this.elevation = elevation; } //getters and setters public String getName() { return this.name; } public String getState() { return this.state; } //... (other getters and setters omitted) //do stuff }</code></pre> <p>And a <code>Places</code> class (a <code>HashMap</code> of <code>Place</code> objects):</p> <pre><code>import java.util.*; public class Places { private Map searchablePlaces; public Places() { searchablePlaces = new HashMap(); } public void add(Place value) { Place key = new Place(value.getName(), value.getState()); searchablePlaces.put(key, value); } public Place find(Place key) { return searchablePlaces.get(key); } //override hashCode, equals //do stuff }</code></pre> <p>Essentially, my question is:</p> <ol> <li>Would there be any efficiency gained in searching the <code>HashMap</code> for <code>key</code>, as opposed to searching for <code>value</code> directly in, let's say, a sorted <code>ArrayList</code>?</li> <li>What if <code>key</code> was of type <code>String</code> equal to <code>name + state</code> (or of type <code>String[2]</code>)?</li> </ol>

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