如何在 Java 中“预先增加”一个 BigInteger？
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How to 'pre increment' a BigInteger in Java?
提问by Andreas Hartmann
I have a forloop with BigIntegers, something like this:
我有一个for带有BigIntegers的循环，如下所示：
for(BigInteger a = BigInteger.valueOf(1); a.compareTo(someBigInteger); ++a) {...
Obviously I can't use the ++operator on a non-primitive. How do I work around this?
显然，我不能++在非原始对象上使用运算符。我该如何解决这个问题？
Also, I have to use BigIntegerin this scenario.
另外，我必须BigInteger在这种情况下使用。
回答by Mureinik
++ais a prefix increment, not a postfix increment, but in the context of a for-loop it doesn't really matter, as you ignore the return value of that statement anyway. In any event, this functionality could be acheieved by calling BigInteger.add. Also note that compareToreturns an int, and since Java does not have implicit casts between ints and booleans (like, e.g., C does), you'd have to compare its result to 0 to see if ais smaller, larger or equal to someBigInteger):
++a是前缀增量，而不是后缀增量，但在 for 循环的上下文中它并不重要，因为您无论如何都会忽略该语句的返回值。无论如何，可以通过调用来实现此功能BigInteger.add。另请注意，compareTo返回 an int，并且由于 Java 在ints 和booleans之间没有隐式转换（例如，C 有），您必须将其结果与 0 进行比较，以查看是否a小于、大于或等于someBigInteger）：
for (BigInteger a = BigInteger.ONE;
a.compareTo(someBigInteger) < 0;
a = a.add(BigInteger.ONE)) {...
回答by Manu
You cannot redefine the operator ++ to work with BigInteger, so the solution is the trivial one: 1) First declare a BigInteger and initialize it 2) In the loop, reassign the BigInteger (a new BigInteger is created when invoking the add method);
您不能重新定义运算符 ++ 以与 BigInteger 一起使用，因此解决方案是微不足道的：1）首先声明一个 BigInteger 并对其进行初始化 2）在循环中，重新分配 BigInteger（调用 add 方法时会创建一个新的 BigInteger） ;
private static final BigInteger LIMIT = new BigInteger("10");
public static void main(String[] args) {
new BigInteger("0");
for (BigInteger a = BigInteger.ZERO; a.compareTo(LIMIT) < 0; a = a.add(new BigInteger("1")))
System.out.println(a);
}
Refer to the documentation http://docs.oracle.com/javase/8/docs/api/java/math/BigInteger.html#add(java.math.BigInteger)
请参阅文档http://docs.oracle.com/javase/8/docs/api/java/math/BigInteger.html#add(java.math.BigInteger)
回答by Dipen Adroja
You can have it like this.
你可以这样拥有它。
for(BigInteger a = BigInteger.ONE; a.compareTo(someBigInteger); a=a.add(BigInteger.ONE)) {.
for(BigInteger a = BigInteger.ONE; a.compareTo(someBigInteger); a=a.add(BigInteger.ONE)) {.
