Question

用Java怎么测试一个对象所占的内存的大小？

Answer 1

这是一个测试的方法，参考网上的，具体可以看提供给你的网址

package com;

public class Sizeof {
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]

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 final Runtime s_runtime = Runtime.getRuntime();
}

Answer 2

声明一个集合，放你要的对象，集合相当于数组，测试它里的内容所占的空间就可以了。

Answer 3

你自己统计类成员变量吧，还包括父类的成员变量，这个是最小的容量。统计这个没什么意义把，有时候父类的东西都私有的你没发统计。

Answer 4

用破解版的