解决方法
The only real disadvantage of immutable classes is that they require a
separate object for each distinct value. Creating these objects can be
costly,especially if they are large. For example,suppose that you
have a million-bit BigInteger and you want to change its low-order
bit:
BigInteger moby = ...; moby = moby.flipBit(0);
The flipBit method
creates a newBigInteger
instance,also a million bits long,that
differs from the original in only one bit. The operation requires time
and space proportional to the size of theBigInteger
. Contrast this tojava.util.BitSet
. LikeBigInteger
,BitSet
represents an arbitrarily
long sequence of bits,but unlikeBigInteger
,BitSet
is mutable. TheBitSet
class provides a method that allows you to change the state of
a single bit of a millionbit instance in constant time.
阅读Item 15: Minimize mutability的完整项目
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