向字节代码注入指令

Question

我需要在代码下面注入一些其他类文件，任何人都可以帮我注入这段代码

long MEGABYTE = 1024L * 1024L;
Runtime runtime = Runtime.getRuntime();
runtime.gc();
long memory = runtime.totalMemory() - runtime.freeMemory();
double memoryUsage=(double)memory/MEGABYTE;