使用代码，查询内存和 jvm的内存

"C:\Program Files\Java\jdk1.8.0_181\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.3\lib\idea_rt.jar=60806:C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_181\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\rt.jar;C:\Users\yzmao\Desktop\zn_wifi_crack-master\target\classes;C:\repository\org\springframework\spring-core\4.3.14.RELEASE\spring-core-4.3.14.RELEASE.jar" com.znkeji.zn_wifi_carck.myApp
JVM内存已用的空间为：3 MB
JVM内存的空闲空间为：118 MB
JVM总内存空间为：121 MB
JVM总内存空间为：1776 MB
======================================
操作系统的版本：Windows 10
操作系统物理内存已用的空间为：1567 MB
操作系统物理内存的空闲空间为：6419 MB
操作系统总物理内存：7986 MB
获得线程总数:

import com.sun.management.OperatingSystemMXBean;

import java.lang.management.ManagementFactory;

public class myApp {
    public static void main(String[] args) throws Exception {

// 虚拟机级内存情况查询
        long vmFree = 0;
        long vmUse = 0;
        long vmTotal = 0;
        long vmMax = 0;
        int byteToMb = 1024 * 1024;
        Runtime rt = Runtime.getRuntime();
        vmTotal = rt.totalMemory() / byteToMb;
        vmFree = rt.freeMemory() / byteToMb;
        vmMax = rt.maxMemory() / byteToMb;
        vmUse = vmTotal - vmFree;
        System.out.println("JVM内存已用的空间为：" + vmUse + " MB");
        System.out.println("JVM内存的空闲空间为：" + vmFree + " MB");
        System.out.println("JVM总内存空间为：" + vmTotal + " MB");
        System.out.println("JVM总内存空间为：" + vmMax + " MB");
        System.out.println("======================================");
        // 操作系统级内存情况查询
        OperatingSystemMXBean osmxb = (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
        String os = System.getProperty("os.name");
        long physicalFree = osmxb.getFreePhysicalMemorySize() / byteToMb;
        long physicalTotal = osmxb.getTotalPhysicalMemorySize() / byteToMb;
        long physicalUse = physicalTotal - physicalFree;
        System.out.println("操作系统的版本：" + os);
        System.out.println("操作系统物理内存已用的空间为：" + physicalFree + " MB");
        System.out.println("操作系统物理内存的空闲空间为：" + physicalUse + " MB");
        System.out.println("操作系统总物理内存：" + physicalTotal + " MB");
        // 获得线程总数
        ThreadGroup parentThread;
        int totalThread = 0;
        for (parentThread = Thread.currentThread().getThreadGroup();
             parentThread.getParent() != null; parentThread = parentThread.getParent()) {
            totalThread = parentThread.activeCount();     }
        System.out.println("获得线程总数:" + totalThread);   }


    }