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PONullPointerException when creating an ArrayList-like class
 

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  1. PONullPointerException when creating an ArrayList-like class
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    <p>As a practice exercise, I am creating my own generic class that is basically a copy of <code>ArrayList</code>. While testing the class with <code>JUnit</code>, I come across a <code>NullPointerException</code> error in the add method:</p> <pre><code>public void add(int index, T element) { if (index &gt; this.size() || index &lt; 0) { throw new IndexOutOfBoundsException(); } if (this.size() == data.length) { // ^ This is the line that the error points to resize(this.data); } for (int i = index; i &lt; this.size; i++) { this.data[i + 1] = this.data[i]; //fix } this.data[index] = element; size++; } </code></pre> <p>After messing around with the class a lot, I can't figure out where the error is coming from. I can provide any details/other parts of the class that are needed. Any guidance as to where the problem is located would be fantastic. Thank You. </p> <p>The constructor for the class:</p> <pre><code>MyArrayList(int startSize) { // round the startSize to nearest power of 2 int pow2 = 1; do { pow2 *= 2; } while (pow2 &lt; startSize); startSize = pow2; this.size = 0; T[] data = (T[]) new Object[startSize]; } </code></pre> <p>The following test case tests the size, but encounters the error when it tries to add an element:</p> <pre><code>public void testSize() { MyArrayList&lt;Integer&gt; test = new MyArrayList&lt;Integer&gt;(); ArrayList&lt;Integer&gt; real = new ArrayList&lt;Integer&gt;(); assertEquals("Size after construction", real.size(), test.size()); test.add(0,5); real.add(0,5); assertEquals("Size after add", real.size(), test.size()); } </code></pre>
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    1. USTroy Alford
    1. USuser1547050
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    1. COWell, `this` can't be `null`, so `data` must be, right?
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      1. USPaul Bellora
 

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