PSYoungGen 有初始空间，为什么没有创建实例，而是使用了一些空间？

Question

/* jvm:" -XX:+PrintGCDetails -Xms20M -Xmx20M -Xmn10M -XX:SurvivorRatio=8 "*/ public class testGC {        private final static int _1MB = 1024*1024;        public static void main(String args[])        {            testAllocation();              }        public static void testAllocation()        {            byte[] allocation1,allocation2,allocation3,allocation4;           System.gc();        }    }运行结果："C:\Program Files\Java\jdk1.8.0_181\bin\java.exe" -XX:+PrintGCDetails -Xms20M -Xmx20M -Xmn10M -XX:SurvivorRatio=8 "-javaagent:C:\Program Files\ JetBrains\IntelliJ IDEA Community Edition 2018.1.6\lib\idea_rt.jar=60552:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.1.6\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 进程以退出代码 0 结束