blocks|key|912944|text|我最近已经这样做了(基于lambdaj代码)，当心它需要您的所有元素都是同一类型(您不能真正添加Byte和BigDecimal)，并且如果不是这样并且不能处理自定义Number，则可能抛出CCE异常。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|912945|public+class+SumAggregator<T+extends+Number>+{
++++public+T+aggregate(Iterable<T>+iterable)+{
++++++++T+result+=+null;
++++++++for+(T+item+:+iterable)+{
++++++++++++result+=+aggregate(result,+item);
++++++++}
++++++++return+result;
++++}


++++@SuppressWarnings("unchecked")
++++protected+T+aggregate(T+first,+T+second)+{
++++++++if+(first+==+null)+{
++++++++++++return+second;
++++++++}+else+if+(second+==+null)+{
++++++++++++return+first;
++++++++}+else+if+(first+instanceof+BigDecimal)+{
++++++++++++return+(T)+aggregate((BigDecimal)+first,+(BigDecimal)+second);
++++++++}+else+if+(second+instanceof+BigInteger)+{
++++++++++++return+(T)+aggregate((BigInteger)+first,+(BigInteger)+second);
++++++++}+else+if+(first+instanceof+Byte)+{
++++++++++++return+(T)+aggregate((Byte)+first,+(Byte)+second);
++++++++}+else+if+(first+instanceof+Double)+{
++++++++++++return+(T)+aggregate((Double)+first,+(Double)+second);
++++++++}+else+if+(first+instanceof+Float)+{
++++++++++++return+(T)+aggregate((Float)+first,+(Float)+second);
++++++++}+else+if+(first+instanceof+Integer)+{
++++++++++++return+(T)+aggregate((Integer)+first,+(Integer)+second);
++++++++}+else+if+(first+instanceof+Long)+{
++++++++++++return+(T)+aggregate((Long)+first,+(Long)+second);
++++++++}+else+if+(first+instanceof+Short)+{
++++++++++++return+(T)+aggregate((Short)+first,+(Short)+second);
++++++++}+else+{
++++++++++++throw+new+UnsupportedOperationException("SumAggregator+only+supports+official+subclasses+of+Number");
++++++++}
++++}

++++private+BigDecimal+aggregate(BigDecimal+first,+BigDecimal+second)+{
++++++++return+first.add(second);
++++}

++++private+BigInteger+aggregate(BigInteger+first,+BigInteger+second)+{
++++++++return+first.add(second);
++++}

++++private+Byte+aggregate(Byte+first,+Byte+second)+{
++++++++return+(byte)+(first+%2B+second);
++++}

++++private+Double+aggregate(Double+first,+Double+second)+{
++++++++return+first+%2B+second;
++++}

++++private+Float+aggregate(Float+first,+Float+second)+{
++++++++return+first+%2B+second;
++++}

++++private+Integer+aggregate(Integer+first,+Integer+second)+{
++++++++return+first+%2B+second;
++++}

++++private+Long+aggregate(Long+first,+Long+second)+{
++++++++return+first+%2B+second;
++++}

++++private+Short+aggregate(Short+first,+Short+second)+{
++++++++return+(short)+(first+%2B+second);
++++}
}|code-block|syntax|javascript|912946|This+code+executed+on+ideone+with+examples。|912947|entityMap|0|LINK|mutability|MUTABLE|url|http://code.google.com/p/lambdaj/|1|http://ideone.com/jkhhp^0|1C|4|1H|A|2A|6|C|7|0|0|0|0|16|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|17|8|@]|D|@$9|18|A|19|1|1A]]|E|$]]|$1|M|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]]]

I've done that recently (based on <a href="http://code.google.com/p/lambdaj/" rel="nofollow">lambdaj</a> code) beware it will need all your elements to be the same type (you can't really add a <code>Byte</code> and a <code>BigDecimal</code>) and can throw a CCE if it isn't the case and won't handle custom <code>Number</code>:

<pre><code>public class SumAggregator&lt;T extends Number&gt; {
 public T aggregate(Iterable&lt;T&gt; iterable) {
 T result = null;
 for (T item : iterable) {
 result = aggregate(result, item);
 }
 return result;
 }


 @SuppressWarnings("unchecked")
 protected T aggregate(T first, T second) {
 if (first == null) {
 return second;
 } else if (second == null) {
 return first;
 } else if (first instanceof BigDecimal) {
 return (T) aggregate((BigDecimal) first, (BigDecimal) second);
 } else if (second instanceof BigInteger) {
 return (T) aggregate((BigInteger) first, (BigInteger) second);
 } else if (first instanceof Byte) {
 return (T) aggregate((Byte) first, (Byte) second);
 } else if (first instanceof Double) {
 return (T) aggregate((Double) first, (Double) second);
 } else if (first instanceof Float) {
 return (T) aggregate((Float) first, (Float) second);
 } else if (first instanceof Integer) {
 return (T) aggregate((Integer) first, (Integer) second);
 } else if (first instanceof Long) {
 return (T) aggregate((Long) first, (Long) second);
 } else if (first instanceof Short) {
 return (T) aggregate((Short) first, (Short) second);
 } else {
 throw new UnsupportedOperationException("SumAggregator only supports official subclasses of Number");
 }
 }

 private BigDecimal aggregate(BigDecimal first, BigDecimal second) {
 return first.add(second);
 }

 private BigInteger aggregate(BigInteger first, BigInteger second) {
 return first.add(second);
 }

 private Byte aggregate(Byte first, Byte second) {
 return (byte) (first + second);
 }

 private Double aggregate(Double first, Double second) {
 return first + second;
 }

 private Float aggregate(Float first, Float second) {
 return first + second;
 }

 private Integer aggregate(Integer first, Integer second) {
 return first + second;
 }

 private Long aggregate(Long first, Long second) {
 return first + second;
 }

 private Short aggregate(Short first, Short second) {
 return (short) (first + second);
 }
}
</code></pre>

<a href="http://ideone.com/jkhhp" rel="nofollow">This code executed on ideone with examples</a>.

blocks|key|912976|text|有几种方法可以将它们组合在一起，但老实说，泛型根本不是这里的方法。为每个具体的原始包装器类型构建一个方法，并分别实现它们。让它泛型太让人头疼了；算术运算不能泛化。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|912977|将其泛化也不会真正获得任何好处。它是如此简单和恒定的代码，你不用担心代码重复，因为它不会改变。而且人们不会将他们自己的数字类型传递给你的代码；它所应用的类型域已经定义得很好并且是有限的。|912978|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

There are ways you can hack this together but in all honestly, generics is simply not the way to go here. Build a method for each concrete primitive wrapper type and implement them separately. It'll be way too much of a headache to make it generic; arithmetic operations can't happen generically.

You don't really gain anything by making it generic, either. It's such simple and constant code that you aren't worried about code duplication, since it's not going to change. And people aren't going to be passing in their own type of Number to your code; the domain of types it applies to is already well defined and finite.

blocks|key|913017|text|您可以使用库，比如Generic+Java+Math+(它的numbers部分)，它为Numer子类提供泛型操作。它提供了一种通用的处理数字的方法，就像在你的例子中一样，但是通过传递算术对象来进行实际计算。请参阅主页上的示例。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|913018|它必须使用盒装类型，所以如果您需要速度，在Java中没有泛型实现可以做到这一点，您必须使用原始类型。|913019|entityMap|0|LINK|mutability|MUTABLE|url|http://code.google.com/p/generic-java-math/^0|9|H|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

You can use a library, such as <a href="http://code.google.com/p/generic-java-math/" rel="nofollow">Generic Java Math</a> (its numbers part), which provides generic operations for Number subclasses. It provides a way to work generically with numbers, just as in your example, but with passing Arithmetics object around, that does the actual calculation. See example on the home page. 
It must use boxed types, so if you need speed, no generic implementation can do that in Java, you must use primitive types.

blocks|key|913061|text|看看下面的例子，用于对任何数字类型的变量列表求和的泛型方法……我相信这就是你所要求的..|type|unstyled|depth|inlineStyleRanges|entityRanges|data|913062|马克·彼得斯的答案也是对的，但这也是一个值得追求的解决方案。|913063|public+class+GenericSum+{
@SuppressWarnings("unchecked")
public+static+<E>+E+sumArray(E[]+inputArray)+{
++++Double+result+=+0.0;
++++//+Sum+array+elements
++++for+(E+element+:+inputArray)+{
++++++++result+=+((Number)+result).doubleValue()
++++++++++++++++%2B+((Number)+element).doubleValue();
++++}
++++return+((E)+result);
}

public+static+void+main(String+args[])+{
++++//+Create+arrays+of+Integer,+Double
++++Integer[]+intArray+=+{+1,+2,+3,+4,+5+};
++++Double[]+doubleArray+=+{+1.1,+2.2,+3.3,+4.4+};

++++System.out.println("Sum+of+doubles+:+"+%2B+sumArray(intArray));
++++System.out.println("Sum+of+doubles+:+"+%2B+sumArray(doubleArray));
}

}|code-block|syntax|javascript|913064|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Have a look at following example of generic method for summation of any Number type of variable lists...
I am sure that this is what you was asking for..

Mark Peters is also right in his answer, but this also is a solution to go for.

<pre><code>public class GenericSum {
@SuppressWarnings("unchecked")
public static &lt;E&gt; E sumArray(E[] inputArray) {
 Double result = 0.0;
 // Sum array elements
 for (E element : inputArray) {
 result = ((Number) result).doubleValue()
 + ((Number) element).doubleValue();
 }
 return ((E) result);
}

public static void main(String args[]) {
 // Create arrays of Integer, Double
 Integer[] intArray = { 1, 2, 3, 4, 5 };
 Double[] doubleArray = { 1.1, 2.2, 3.3, 4.4 };

 System.out.println("Sum of doubles : " + sumArray(intArray));
 System.out.println("Sum of doubles : " + sumArray(doubleArray));
}

}
</code></pre>

I want to make a generic method which makes the total sum of a <code>List</code> of numbers.

What I was trying is this:

<pre><code>public static &lt;T extends Number&gt; T sumList(List&lt;T&gt; data)
{
 T total = 0;
 for (T elem : data)
 {
 total += elem;
 }
 return total;
}
</code></pre>

But the problem is that <code>there is no += operator in T</code> and that <code>total can't be assigned to zero</code>.

How can I do this?

Thanks

Java: Generic methods and numbers

Java

我想做一个泛型方法，使一个数字的List的总和。我尝试的是这样的：public static <T extends Number> T sumList(List<T> data){ T total = 0; for (T elem : data) { total += elem; ...

问Java:泛型方法和数字
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