java - 计算分配对象所需的内存

Question

我想比较内存使用情况，分配 Calendar 对象和 Joda 的 DateTime 对象。

// How much memory required to allocate 100 Calendar objects?
for (int i = 0; i < 100; i++) {
    Calendar c = Calendar.getInstance();
    l = l + c.getTimeInMillis();
    CalendarList.add(c);
}

// How much memory required to allocate Joda TimeDate objects?
for (int i = 0; i < 100; i++) {
    DateTime dateTime = new DateTime();
    l = l + dateTime.getMillis();
    DateTimeList.add(dateTime);
}

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我可以知道是否可以添加任何代码来进行测量？

Answer 1

使用检测获取内存使用情况的提示:

public class MemUsage {

    public static void main(String[] args) {
        Instrumentation instr = InstrumentationAgent.getInstrumentation();
        if (instr == null) {
            System.err.println("No Instrumentation, use the VM option \"-javaagent:Instrumentation.jar\"");
            return;
        }
        System.out.println();
        System.out.println("an implementation-specific approximation of the amount of storage");
        System.out.println("Calendar = " + instr.getObjectSize(Calendar.getInstance()));
        System.out.println();
    }
}

其他选项:MemoryMXBean但我从未使用过它。