gc日志设置并解读

打印gc日志参数-XX:+PrintGC

gc日志解读
[GC (System.gc())  17988K->8276K(251392K), 0.0045549 secs]
[Full GC (System.gc())  8276K->8122K(251392K), 0.0066128 secs]
17988K是回收前的值
8276K是回收后的大小

gc日志测试用例
public class LocalVarGC {

    public void localvarGc1(){
        byte[] a=new byte[6*1024*1024];
        System.gc();
    }
    public void localvarGc2(){
        byte[] a=new byte[6*1024*1024];
        a=null;
        System.gc();
    }
    public void localvarGc3(){
        {
            byte[] a=new byte[6*1024*1024];
        }
        System.gc();
    }
    public void localvarGc4(){
        {
            byte[] a=new byte[6*1024*1024];
        }
        int c=10;
        System.gc();
    }
    public void localvarGc5(){
        localvarGc1();
        System.gc();
    }
    public static void main(String[] args) {
        LocalVarGC ins=new LocalVarGC();
        ins.localvarGc5();
    }

}