判断某个java对象占用内存情况

Sizeof.java

public class Sizeof {
    public static void main(String[] args) throws Exception {
        // "warm up" all classes/methods that we are going to use:
        runGC();
        usedMemory();

        // array to keep strong references to allocated objects:
        final int count = 10000; // 10000 or so is enough for small ojects
        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;

            // INSTANTIATE YOUR DATA HERE AND ASSIGN IT TO 'object':

            object = YOUR OBJECT;
            // end your code here
            if (i >= 0) {
                objects[i] = object;
            } else {
                object = null; // discard the "warmup" 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");
    }

    // a helper method for creating Strings of desired length
    // and avoiding getting tricked by String interning:
    public static String createString(final int length) {
        final char[] result = new char[length];
        for (int i = 0; i < length; ++i) {
            result[i] = (char) i;
        }

        return new String(result);
    }

    // this is our way of requesting garbage collection to be run:
    // [how aggressive it is depends on the JVM to a large degree, but
    // it is almost always better than a single Runtime.gc() call]
    private static void runGC() throws Exception {
        // for whatever reason 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 < 1000); ++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();

} // end of class