小弟用java3、4年了 想深入研究一上。有没有关于java内存，线程等方面介绍的书籍

import java.io.*;import com.sun.management.OperatingSystemMXBean;import sun.management.ManagementFactory;public class Tst{    public static String pt="D:\\abc.txt";    public Tst(){    }    public static void main(String[] args) throws Exception{        //free和use和total均为KB        long free=0;        long use=0;        long total=0;        int kb=1024;        Runtime rt=Runtime.getRuntime();        total=rt.totalMemory();        free=rt.freeMemory();        use=total-free;        System.out.println("系统内存已用的空间为："+use/kb+" MB");        System.out.println("系统内存的空闲空间为："+free/kb+" MB");        System.out.println("系统总内存空间为："+total/kb+" MB");        OperatingSystemMXBean osmxb = (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();        long physicalFree=osmxb.getFreePhysicalMemorySize()/kb;        long physicalTotal=osmxb.getTotalPhysicalMemorySize()/kb;        long physicalUse=physicalTotal-physicalFree;        String os=System.getProperty("os.name");        System.out.println("操作系统的版本："+os);        System.out.println("系统物理内存已用的空间为："+physicalFree+" MB");        System.out.println("系统物理内存的空闲空间为："+physicalUse+" MB");        System.out.println("总物理内存："+physicalTotal+" MB");        // 获得线程总数        ThreadGroup parentThread;        for (parentThread = Thread.currentThread().getThreadGroup(); parentThread                .getParent() != null; parentThread = parentThread.getParent())            ;        int totalThread = parentThread.activeCount();        System.out.println("获得线程总数:"+totalThread);    }    }