java 如何检查 BigInteger 是否为空

How to check if a BigInteger is null

提问by gnsb

I have a code which may assign null to a BigInteger. I need to check if it is null or not.

我有一个代码可以将 null 分配给 BigInteger。我需要检查它是否为空。

I've tried the following things, and they do not work:

我尝试了以下事情，但它们不起作用：

1. ==will just check the reference, not the value.

   BigInteger x = BigInteger.ONE;
   
   if(x== null)
   {
       System.out.println( x );
   }
   

1. ==只会检查引用，而不是值。

   BigInteger x = BigInteger.ONE;
   
   if(x== null)
   {
       System.out.println( x );
   }
   

Output of above is it prints x. (Somehow the boolean condition is satisfied, even though x is not null).

上面的输出是打印 x。（以某种方式满足布尔条件，即使 x 不为空）。

1. Following gives NullPointerException upon comparing

   BigInteger x = BigInteger.ONE;
   BigInteger myNull = null;
   
   if(x.compareTo(myNull) == 0 )
   {
       System.out.println( x );
   }
   

2. Another NPE:

   BigInteger x = BigInteger.ONE;
   
   if(x.compareTo(null) == 0)
   {
       System.out.println( x );
   }
   

2. 以下在比较时给出 NullPointerException

   BigInteger x = BigInteger.ONE;
   BigInteger myNull = null;
   
   if(x.compareTo(myNull) == 0 )
   {
       System.out.println( x );
   }
   

3. 另一个 NPE：

   BigInteger x = BigInteger.ONE;
   
   if(x.compareTo(null) == 0)
   {
       System.out.println( x );
   }
   

How do I check if a BigInteger is null properly?

如何检查 BigInteger 是否正确为空？

回答by Robin Krahl

There is a difference between a nullreference and an object with the value 0. To check for nullreferences, use:

null引用和值为 0 的对象之间存在差异。要检查null引用，请使用：

BigInteger value = getValue();
if (value != null) {
  // do something
}

To check for the value 0, use:

要检查值 0，请使用：

BigInteger value = getValue();
if (!BigInteger.ZERO.equals(value)) {
  // do something
}

To ensure the object is neither a nullreference nor has the value 0, combine both:

为确保对象既不是null引用也不是值 0，请将两者结合起来：

BigInteger value = getValue();
if (value != null && !value.equals(BigInteger.ZERO)) {
  // do something
}

---

---

2015-06-26: Edited according to @Arpit's comment.

2015-06-26：根据@Arpit 的评论进行编辑。

回答by Bathsheba

.compareTo(arg)throws a NullPointerException if argis null.

.compareTo(arg)如果arg是，则抛出 NullPointerException null。

You should check if argis nullprior to calling the method.

您应该检查是否arg是null之前调用该方法。