今天面试问道JDK8默认使用的垃圾收集器是什么，然后回来第一时间CMD命令查看了一下：
java -XX:+PrintCommandLineFlags -version -XX:InitialHeapSize=266390080 -XX:MaxHeapSize=4262241280 -XX:+PrintCommandLineFlags -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC java version "1.8.0_191" Java(TM) SE Runtime Environment (build 1.8.0_191-b12) Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode) UseParallelGC 即 Parallel Scavenge + Parallel Old,再查看详细信息
java -XX:+PrintGCDetails -version java version "1.8.0_191" Java(TM) SE Runtime Environment (build 1.8.0_191-b12) Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode) Heap PSYoungGen total 76288K, used 2621K [0x000000076b500000, 0x0000000770a00000, 0x00000007c0000000) eden space 65536K, 4% used [0x000000076b500000,0x000000076b78f748,0x000000076f500000) from space 10752K, 0% used [0x000000076ff80000,0x000000076ff80000,0x0000000770a00000) to space 10752K, 0% used [0x000000076f500000,0x000000076f500000,0x000000076ff80000) ParOldGen total 175104K, used 0K [0x00000006c1e00000, 0x00000006cc900000, 0x000000076b500000) object space 175104K, 0% used [0x00000006c1e00000,0x00000006c1e00000,0x00000006cc900000) Metaspace used 2291K, capacity 4480K, committed 4480K, reserved 1056768K class space used 254K, capacity 384K, committed 384K, reserved 1048576K