计算类大小

package com.taobao.matrix.tbtry;

import java.util.Date;

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;
        InviterBean[] objects = new InviterBean[count];

        long heap1 = 0;
        // Allocate count+1 objects, discard the first one
       
        for (int i = -1; i < count; ++i) {
            InviterBean object = null;

            // Instantiate your data here and assign it to object

            object = new InviterBean("nickkijiuyg"+i,124L,34,new Date());
            //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");
    }

    private static void runGC() throws Exception {
        // It helps to call Runtime.gc()
        // using several method calls:
        for (int r = 0; r < 4; ++r)
            _runGC();
    }

    @SuppressWarnings("static-access")
    private static void _runGC() throws Exception {
        try{
            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();
            }
        }catch(Exception e) {
            System.out.println(e);
        }
    }

    private static long usedMemory() {
        return s_runtime.totalMemory() - s_runtime.freeMemory();
    }

    private static final Runtime s_runtime = Runtime.getRuntime();
} // End of class