java - BigInteger 使用多少空间？

Question

BigInteger 对象通常使用多少字节的内存？

Answer 1

BigInteger 在内部使用 int[] 来表示您使用的大数字。因此它确实取决于您存储在其中的数字的大小。如果当前数字不适合动态，则 int[] 将增长。

要获取您的BigInteger 实例当前 使用的字节数，您可以使用Instrumentation 接口(interface)，尤其是getObjectSize(Object)。 .

import java.lang.instrument.Instrumentation;

public class ObjectSizeFetcher {
    private static Instrumentation instrumentation;

    public static void premain(String args, Instrumentation inst) {
        instrumentation = inst;
    }

    public static long getObjectSize(Object o) {
        return instrumentation.getObjectSize(o);
    }
}

为了说服自己，请查看 source code ，它说:

/**
 * The magnitude of this BigInteger, in <i>big-endian</i> order: the
 * zeroth element of this array is the most-significant int of the
 * magnitude.  The magnitude must be "minimal" in that the most-significant
 * int ({@code mag[0]}) must be non-zero.  This is necessary to
 * ensure that there is exactly one representation for each BigInteger
 * value.  Note that this implies that the BigInteger zero has a
 * zero-length mag array.
 */
final int[] mag;