pretendedMemory.add(builder.toString());
}
int deleteCount = new Random().nextInt(15000);
for (int i = -1; ++i != deleteCount; )
pretendedMemory.removeFirst();
System.out.println("-----------");
}
}
}
).start();
}
private Runtime context;
private double maxFreeMemory;
private long lastFreeMemory;
private long lastTotalMemory;
private long lastMaxMemory;
private double lastMemoryRate;
public PerformanceMonitor(Runtime context)
{
this.context = context;
}
public void checkAll()
{
this.monitorMemory();
this.monitorCpu();
}
/**
* 本方法比较当前空余内存与历史记录最大空余内存的关系。若空余内存过小，则执行垃圾回收。
*/
public void monitorMemory()
{
// 求空余内存，并计算空余内存比起最大空余内存的比例
long freeMemory = this.context.freeMemory();
if (freeMemory > this.maxFreeMemory)
this.maxFreeMemory = Long.valueOf(freeMemory).doubleva lue();
double memoryRate = freeMemory / this.maxFreeMemory;
System.out.println("There are " + memoryRate * 100 + "% free memory.");
// 如果内存空余率在变小，则一切正常；否则需要报告内存变化情况
if (memoryRate >= this.lastMemoryRate) this.reportMemoryChange();
// 如果内存空余率很低，则执行内存回收
if (freeMemory / this.maxFreeMemory < 0.3)
System.out.print("System will start memory Garbage Collection.");
System.out.println(" Now we have " + freeMemory / 1000 + " KB free memory.");
this.context.gc();
System.out.println("After the Garbage Collection, we have "
+ this.context.freeMemory() / 1000 + " KB free memory.");
}
// 记录内存信息
this.recordMemoryInfo(memoryRate);
}
/**
* 报告内存变化情况
*/
private void reportMemoryChange()
{
System.out.print("Last freeMemory = " + this.lastFreeMemory / 1000 + " KB,");
System.out.println(" now it is " + this.context.freeMemory() / 1000 + " KB.");
System.out.print("Last totalMemory = " + this.lastTotalMemory / 1000 + " KB,");
System.out.println(" now it is " + this.context.totalMemory() / 1000 + " KB.");
System.out.print("Last maxMemory = " + this.lastMaxMemory / 1000 + " KB,");
System.out.println(" now it is " + this.context.maxMemory() / 1000 + " KB.");
}
/**
* 记录本次内存信息。
*/
private void recordMemoryInfo(double memoryRate)
{
this.lastFreeMemory = this.context.freeMemory();
this.lastMaxMemory = this.context.maxMemory();
this.lastTotalMemory = this.context.totalMemory();
this.lastMemoryRate = memoryRate;
}
/**
* 监测 CPU 的方法。
*/
public void monitorCpu()
{
int cpuCount = this.context.availableProcessors();
if (cpuCount > 1) System.out.println("CPU have " + cpuCount + " processors.");
}
}
我运行这段程序，得到结果报告。通过观察结果报告，我得到了一些新结论。
首先， maxMemory 在一台机器只运行一个爪哇（Java）虚拟机的前提下，一般来说并不会变动。
其次，新生代内存会很快地自动回收，这体现在 freeMemory 总是不断少量自动增加上。
最后，爪哇（Java）虚拟机会在内存不足时，自己申请新的内存。这个内存空间也能够根据报告大概看