/** 47 - 演示Full GC

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*/

public class Test4 {

public static void main(String[] args) {

byte[] arr1 = new byte[4 * 1024 *1024]; //这里4M是大对象 直接进入老年代

arr1 = null;

byte[] arr2 = new byte[2 * 1024 *1024];

byte[] arr3 = new byte[2 * 1024 *1024];

byte[] arr4 = new byte[128 *1024];

byte[] arr5 = new byte[2 * 1024 *1024];

byte[] arr6 = new byte[2 * 1024 *1024];//这里Young G

/* javac -encoding UTF-8 Test4.java

java -XX:NewSize=10485760 -XX:MaxNewSize=10485760 -XX:InitialHeapSize=20971520 -XX:MaxHeapSize=20971520 -XX:SurvivorRatio=8 -XX:MaxTenuringThreshold=15 -XX:PretenureSizeThreshold=3145728 -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -Xloggc:D:\\gc.log Test4

这里 PretenureSizeThreshold = 3M 大于3M的对象 视为大对象，直接进入老年代

*/

/*

Java HotSpot(TM) 64-Bit Server VM (25.45-b02) for windows-amd64 JRE (1.8.0_45-b14), built on Apr 10 2015 10:34:15 by "java_re" with MS VC++ 10.0 (VS2010)

Memory: 4k page, physical 16657288k(9795016k free), swap 17705864k(9994480k free)

CommandLine flags: -XX:InitialHeapSize=20971520 -XX:MaxHeapSize=20971520 -XX:MaxNewSize=10485760 -XX:MaxTenuringThreshold=15 -XX:NewSize=10485760 -XX:OldPLABSize=16 -XX:PretenureSizeThreshold=3145728 -XX:+PrintGC -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:SurvivorRatio=8 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseConcMarkSweepGC -XX:-UseLargePagesIndividualAllocation -XX:+UseParNewGC

0.075: [GC (Allocation Failure) 0.075: [ParNew (promotion failed): 7463K->8253K(9216K), 0.0024929 secs]0.078: [CMS: 8194K->6894K(10240K), 0.0024192 secs] 11559K->6894K(19456K), [Metaspace: 2547K->2547K(1056768K)], 0.0052541 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]

Heap

par new generation total 9216K, used 2130K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)

eden space 8192K, 26% used [0x00000000fec00000, 0x00000000fee14930, 0x00000000ff400000)

from space 1024K, 0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)

to space 1024K, 0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)

concurrent mark-sweep generation total 10240K, used 6894K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)

Metaspace used 2553K, capacity 4486K, committed 4864K, reserved 1056768K

class space used 274K, capacity 386K, committed 512K, reserved 1048576K

20行开始Young GC ParNew (promotion failed): 7463K->8253K(9216K) ，因为S区放不下6M多存活对象，于是将6M多对象放到老年代中去，但是老年代已经有了4M对象，放不下6M了，

于是触发了Full GC:CMS: 8194K->6894K(10240K) 回收了arr1垃圾对象 ，同时将6M多新生代对象放到老年代了

最后将arr6对应的2M对象在Eden区创建了

*/

}

}