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POImplementing a Map in Java
 

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    <p>I'm currently working on an assignment that has me creating a Map class in Java, and I've run into an error while working with the 'put' method that I cannot seem to fix. Essentially, when the test is run, the new Node within the Map will not be created, and I cannot seem to figure out why. Thank you in advance!</p> <p>Class:</p> <pre><code>public class MyMap&lt;K extends Comparable&lt;K&gt;, V&gt; { private class MapNode { private K key; private V value; private MapNode left; private MapNode right; public MapNode(K theKey, V theValue) { key = theKey; value = theValue; left = null; right = null; } } private MapNode root; public MyMap() { root = null; } /** * Associates key to value and stores mapping If key exists, replaces value * with a new value * * @param key * @param value * @return value replaced; null if no value */ public V put(K key, V value) { return put(key, value, root); } private V put(K key, V value, MapNode ref) { V temp; if (ref == null) { ref = new MapNode(key, value); return null; } else { if (ref.key.compareTo(key) == 0) { temp = ref.value; ref.value = value; return temp; } else if (key.compareTo(ref.key) &lt; 0) return put(key, value, ref.left); else return put(key, value, ref.right); } } /** * Return value to which key is mapped * * @param key * @return value of key; null */ public V get(K key) { return get(key, root); } private V get(K key, MapNode ref) { if (ref == null) { return null; } else { if (ref.key.compareTo(key) == 0) return ref.value; else if (key.compareTo(ref.key) &lt; 0) return get(key, ref.left); else if (key.compareTo(ref.key) &gt; 0) return get(key, ref.right); else return null; } } /** * Returns true if Map already uses the key * * @param key * @return true; false */ public boolean containsKey(K key) { return containsKey(key, root); } private boolean containsKey(K key, MapNode ref) { if (ref == null) { return false; } else { if (ref.key.compareTo(key) == 0) return true; else if (key.compareTo(ref.key) &lt; 0) return containsKey(key, ref.left); else if (key.compareTo(ref.key) &gt; 0) return containsKey(key, ref.right); else return false; } } } </code></pre> <p>Test:</p> <pre><code>import org.junit.Test; import static org.junit.Assert.assertEquals; import static org.junit.Assert.assertFalse; import static org.junit.Assert.assertTrue; public class MyMapTest { @Test public void testMyMap(){ MyMap&lt;String, Integer&gt; m = new MyMap&lt;String, Integer&gt;(); assertFalse(m.containsKey("one")); assertEquals(null, m.get("one")); assertEquals(null, m.put("one", 1)); assertTrue(m.containsKey("one")); } } </code></pre>
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    1. PTQuestion
    1. USMat
    1. USWeasler
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      1. VTUpMod
    1. COWhat kind of Map is this? Some kind of Binary Tree?
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      1. POImplementing a Map in Java
      1. USSam DeHaan
    2. COWhen you step through your code in a debugger what do you see?
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      1. POImplementing a Map in Java
      1. USPeter Lawrey
    3. COYes, a Binary tree that stores both a Key and a Value at each location.
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      1. USWeasler
 

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