最大堆大小：

Runtime.getRuntime().maxMemory();

您可能会发现一些有趣的其他计算：

Runtime runtime = Runtime.getRuntime();
long maxMemory = runtime.maxMemory();
long allocatedMemory = runtime.totalMemory();
long freeMemory = runtime.freeMemory();
long totalFreeMemory = freeMemory + (maxMemory - allocatedMemory);
long usedMemory = maxMemory - totalFreeMemory;