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POjava why different memory usage for primitive versus object array in 2D
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  1. POjava why different memory usage for primitive versus object array in 2D
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    copied!<p>Relevant code</p> <pre><code>int row = 100000; int col = 18; Object[][] objectArray = new Object[row][1]; int[][] intArray = new int[row][1]; System.out.println("Size of objectArray = " + net.sourceforge.sizeof.SizeOf.deepSizeOf(objectArray) + " bytes"); System.out.println("Size of intArray = " + net.sourceforge.sizeof.SizeOf.deepSizeOf(intArray) + " bytes"); Object[][] objectMatrix = new Object[row][col]; int[][] intMatrix = new int[row][col]; System.out.println("Size of objectMatrix = " + net.sourceforge.sizeof.SizeOf.deepSizeOf(objectMatrix) + " bytes"); System.out.println("Size of intMatrix = " + net.sourceforge.sizeof.SizeOf.deepSizeOf(intMatrix) + " bytes"); </code></pre> <p>Relevant output</p> <pre><code>Size of objectArray = 4000024 bytes Size of intArray = 4000024 bytes Size of objectMatrix = 17600024 bytes Size of intMatrix = 10400024 bytes </code></pre> <p>If instead of 1D (number of cols=1), I have 2D (number of cols > 1), the object matrix takes more space.</p> <p>Can someone explain the reason?</p> <p>Edit: Added another case with just one row</p> <pre><code> int row = 1; int col = 2; Object[][] objectArray = new Object[row][1]; int[][] intArray = new int[row][1]; System.out.println("Size of objectArray = " + net.sourceforge.sizeof.SizeOf.deepSizeOf(objectArray) + " bytes"); System.out.println("Size of intArray = " + net.sourceforge.sizeof.SizeOf.deepSizeOf(intArray) + " bytes"); Object[][] objectMatrix = new Object[row][col]; int[][] intMatrix = new int[row][col]; System.out.println("Size of objectMatrix = " + net.sourceforge.sizeof.SizeOf.deepSizeOf(objectMatrix) + " bytes"); System.out.println("Size of intMatrix = " + net.sourceforge.sizeof.SizeOf.deepSizeOf(intMatrix) + " bytes"); </code></pre> <p>Output</p> <pre><code>Size of objectArray = 64 bytes Size of intArray = 64 bytes Size of objectMatrix = 72 bytes Size of intMatrix = 64 bytes </code></pre>
 

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