JVM打印GC信息

-XX:+PrintGCDetails

public class GcDemo {
    public static void main(String[] args) {
        Object obj = new Object();
        obj = null;
        System.gc();
    }
}

[GC (System.gc()) [PSYoungGen: 5242K->872K(152576K)] 5242K->880K(500736K), 0.0011529 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 
[Full GC (System.gc()) [PSYoungGen: 872K->0K(152576K)] [ParOldGen: 8K->625K(348160K)] 880K->625K(500736K), [Metaspace: 3130K->3130K(1056768K)], 0.0042044 secs] [Times: user=0.00 sys=0.02, real=0.01 secs] 
Heap
 PSYoungGen      total 152576K, used 3932K [0x0000000716000000, 0x0000000720a00000, 0x00000007c0000000)
  eden space 131072K, 3% used [0x0000000716000000,0x00000007163d7290,0x000000071e000000)
  from space 21504K, 0% used [0x000000071e000000,0x000000071e000000,0x000000071f500000)
  to   space 21504K, 0% used [0x000000071f500000,0x000000071f500000,0x0000000720a00000)
 ParOldGen       total 348160K, used 625K [0x00000005c2000000, 0x00000005d7400000, 0x0000000716000000)
  object space 348160K, 0% used [0x00000005c2000000,0x00000005c209c5e0,0x00000005d7400000)
 Metaspace       used 3144K, capacity 4496K, committed 4864K, reserved 1056768K
  class space    used 341K, capacity 388K, committed 512K, reserved 1048576K