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Java Memory Consumption per Object
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| package org.aigor; | |
| /** | |
| * Java Memory Consumption per Object | |
| * | |
| * Based on article: | |
| * http://www.javaworld.com/article/2077496/testing-debugging/java-tip-130--do-you-know-your-data-size-.html | |
| * By Vladimir Roubtsov | |
| */ | |
| public class MemoryTest { | |
| private static final Runtime s_runtime = Runtime.getRuntime (); | |
| public static void main (String [] args) throws Exception | |
| { | |
| // Warm up all classes/methods we will use | |
| runGC (); | |
| usedMemory (); | |
| // Array to keep strong references to allocated objects | |
| final int count = 100000; | |
| Object [] objects = new Object [count]; | |
| long heap1 = 0; | |
| // Allocate count+1 objects, discard the first one | |
| for (int i = -1; i < count; ++ i) | |
| { | |
| Object object = null; | |
| // Instantiate your data here and assign it to object | |
| object = new Object (); | |
| //object = new Integer (i); | |
| //object = new Long (i); | |
| //object = new String (); | |
| //object = new byte [128][1]; | |
| //object = generateString(0, 1); | |
| // int stringCount = 100000; | |
| // int stringLength = 10; | |
| // object = new ArrayList<>(stringCount); | |
| // for (int j = 0; j < stringCount; j++){ | |
| // ((List)object).add(generateString(stringLength, i)); | |
| // } | |
| if (i >= 0) | |
| objects [i] = object; | |
| else | |
| { | |
| object = null; // Discard the warm up object | |
| runGC (); | |
| heap1 = usedMemory (); // Take a before heap snapshot | |
| } | |
| } | |
| runGC (); | |
| long heap2 = usedMemory (); // Take an after heap snapshot: | |
| final int size = Math.round (((float)(heap2 - heap1))/count); | |
| System.out.println ("'before' heap: " + heap1 + | |
| ", 'after' heap: " + heap2); | |
| System.out.println ("heap delta: " + (heap2 - heap1) + | |
| ", {" + objects [0].getClass () + "} size = " + size + " bytes"); | |
| for (int i = 0; i < count; ++ i) objects [i] = null; | |
| objects = null; | |
| } | |
| private static void runGC () throws Exception { | |
| // It helps to call Runtime.gc() | |
| // using several method calls: | |
| for (int r = 0; r < 4; ++ r) _runGC (); | |
| } | |
| private static void _runGC () throws Exception { | |
| long usedMem1 = usedMemory (), usedMem2 = Long.MAX_VALUE; | |
| for (int i = 0; (usedMem1 < usedMem2) && (i < 500); ++ i) | |
| { | |
| s_runtime.runFinalization (); | |
| s_runtime.gc (); | |
| Thread.currentThread ().yield (); | |
| usedMem2 = usedMem1; | |
| usedMem1 = usedMemory (); | |
| } | |
| } | |
| private static long usedMemory () { | |
| return s_runtime.totalMemory () - s_runtime.freeMemory (); | |
| } | |
| private static String generateString(int length, int start){ | |
| char[] chars = new char[length]; | |
| for (int i = 0; i < length ; i++){ | |
| chars[i] = (char) (i + start); | |
| } | |
| return new String(chars); | |
| } | |
| } |
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