blocks|key|1450632|text|在Java6中，除了添加@SuppressWarnings("unchecked")之外，我不这么认为。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1450633|此bug+report包含更多信息，但归根结底是编译器不喜欢泛型类型数组。|1450634|entityMap|0|LINK|mutability|MUTABLE|url|http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6227971^0|C|U|0|1|A|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@]|D|@$9|T|A|U|1|V]]|E|$]]|$1|H|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

In Java 6, other than adding <code>@SuppressWarnings(&quot;unchecked&quot;)</code>, I don't think so.
This <a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6227971" rel="nofollow noreferrer">bug report</a> has more information but it boils down to the compiler not liking arrays of generic types.

blocks|key|1450704|text|这是一个很容易解决的问题:使用List<T>！|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1450705|应该避免引用类型的数组。|1450706|在当前版本的Java+(1.7)中，您可以使用@SafeVargs标记方法，这将删除调用者的警告。不过要小心，没有遗留的数组也会更好。|1450707|在获得适当的文字表示之前，List.of()提供了一种相对简洁的方式来编写(不可修改的)+List。|1450708|另请参阅Improved+Compiler+Warnings+and+Errors+When+Using+Non-Reifiable+Formal+Parameters+with+Varargs+Methods技术说明。|1450709|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/7/docs/api/java/lang/SafeVarargs.html|1|http://docs.oracle.com/javase/7/docs/technotes/guides/language/non-reifiable-varargs.html^0|F|7|0|0|N|A|N|A|0|0|D|9|19|4|0|4|2T|1|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|10|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@$9|14|A|15|1|16]]|E|$]]|$1|J|3|K|5|6|7|17|8|@$9|18|A|19|B|C]|$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|L|3|M|5|6|7|1C|8|@]|D|@$9|1D|A|1E|1|1F]]|E|$]]|$1|N|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]]|O|$P|$5|Q|R|S|E|$T|U]]|V|$5|Q|R|S|E|$T|W]]]]

It is a very easy problem to solve: Use <code>List&lt;T&gt;</code>!
Arrays of reference type should be avoided.
In the current version of Java (1.7), you can mark method with <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/SafeVarargs.html" rel="nofollow noreferrer"><code>@SafeVargs</code></a> which will remove the warning from the caller. Careful with that though, and you're still better off without legacy arrays.
<code>List.of()</code> provides a relatively concise way of writing an (unmodifiable) <code>List</code> until Java gains an appropriate literal representation.
See also the <a href="http://docs.oracle.com/javase/7/docs/technotes/guides/language/non-reifiable-varargs.html" rel="nofollow noreferrer">Improved Compiler Warnings and Errors When Using Non-Reifiable Formal Parameters with Varargs Methods</a> tech note.

blocks|key|1450784|text|当使用泛型类型的数组时，我被迫传递对泛型类型的引用。这样，我就可以使用java.lang.reflect.Array编写泛型代码了。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1450785|http://java.sun.com/javase/6/docs/api/java/lang/reflect/Array.html|offset|length|1450786|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|1U|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

When workings with arrays of generic type, I am forced to pass a reference to the generic type. With that, I can actually do the generic code, using java.lang.reflect.Array.

<a href="http://java.sun.com/javase/6/docs/api/java/lang/reflect/Array.html" rel="nofollow noreferrer">http://java.sun.com/javase/6/docs/api/java/lang/reflect/Array.html</a>

blocks|key|1450825|text|你可以重载这些方法。这不能解决您的问题，但它可以最大限度地减少警告的数量(是的，这是一种攻击！)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1450826|class+Assembler<X,+Y>+{
++void+assemble(X+container,+Y+a1)+{+...+}
++void+assemble(X+container,+Y+a1,+Y+a2)+{+...+}
++void+assemble(X+container,+Y+a1,+Y+a2,+Y+a3)+{+...+}
++void+assemble(X+container,+Y+a1,+Y+a2,+Y+a3,+Y+a4)+{+...+}
++void+assemble(X+container,+Y...+args)+{+...+}
}|code-block|syntax|javascript|1450827|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can have overload the methods.
This does not solve your problem but it minimizes the number of warnings (and yes, it's a hack!)

<pre><code>class Assembler&lt;X, Y&gt; {
 void assemble(X container, Y a1) { ... }
 void assemble(X container, Y a1, Y a2) { ... }
 void assemble(X container, Y a1, Y a2, Y a3) { ... }
 void assemble(X container, Y a1, Y a2, Y a3, Y a4) { ... }
 void assemble(X container, Y... args) { ... }
}
</code></pre>

blocks|key|1450868|text|在Java7中，使用@SafeVarargs注释方法声明|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1450869|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/7/docs/api/java/lang/SafeVarargs.html^0|A|C|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

In Java 7, annotate the method declaration with <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/SafeVarargs.html" rel="nofollow noreferrer">@SafeVarargs</a>

blocks|key|1450964|text|在vararg方法调用中显式地将参数转换为Object将使编译器满意，而无需求助于@SuppressWarning。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1450965|public+static+<T>+List<T>+list(+final+T...+items+)
{
++++return+Arrays.asList(+items+);
}

//+This+will+produce+a+warning.
list(+"1",+2,+new+BigDecimal(+"3.5"+)+)

//+This+will+not+produce+a+warning.
list(+(Object)+"1",+(Object)+2,+(Object)+new+BigDecimal(+"3.5"+)+)

//+This+will+not+produce+a+warning+either.+Casting+just+the+first+parameter+to+
//+Object+appears+to+be+sufficient.
list(+(Object)+"1",+2,+new+BigDecimal(+"3.5"+)+)|code-block|syntax|javascript|1450966|我认为这里的问题是编译器需要找出要创建的具体类型的数组。如果该方法不是泛型，则编译器可以使用该方法中的类型信息。如果该方法是泛型的，它会尝试根据调用时使用的参数来确定数组类型。如果参数类型是同源的，那么这项任务就很简单。如果它们不同，在我看来，编译器试图变得太聪明，并创建了一个联合类型的泛型数组。然后，它会觉得有必要警告你。更简单的解决方案是在无法更好地缩小类型范围时创建Object[]。上面的解决方案正是强制这样做的。|1450967|为了更好地理解这一点，与下面的list2方法相比，尝试调用上面的list方法。|1450968|public+static+List<Object>+list2(+final+Object...+items+)
{
++++return+Arrays.asList(+items+);
}|1450969|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Explicitly casting parameters to Object in vararg method invocation will make the compiler happy without resorting to @SuppressWarnings.

<pre><code>public static &lt;T&gt; List&lt;T&gt; list( final T... items )
{
 return Arrays.asList( items );
}

// This will produce a warning.
list( "1", 2, new BigDecimal( "3.5" ) )

// This will not produce a warning.
list( (Object) "1", (Object) 2, (Object) new BigDecimal( "3.5" ) )

// This will not produce a warning either. Casting just the first parameter to 
// Object appears to be sufficient.
list( (Object) "1", 2, new BigDecimal( "3.5" ) )
</code></pre>

I believe the issue here is that the compiler needs to figure out what concrete type of array to create. If the method is not generic, the compiler can use type information from the method. If the method is generic, it tries to figure out the array type based on parameters used at invocation. If the parameter types are homogenic, that task is easy. If they vary, the compiler tries to be too clever in my opinion and creates a union-type generic array. Then it feels compelled to warn you about it. A simpler solution would have been to create Object[] when type cannot be better narrowed down. The above solution forces just that.

To understand this better, play around with invocations to the above list method compared to the following list2 method.

<pre><code>public static List&lt;Object&gt; list2( final Object... items )
{
 return Arrays.asList( items );
}
</code></pre>

blocks|key|1236251|text|从Java7开始，您就可以将@SafeVarargs添加到方法中，并且您不必在客户端代码上进行注释。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1236252|class+Assembler<X,+Y>+{

++++@SafeVarargs
++++final+void+assemble(X+container,+Y...+args)+{
++++++++//has+to+be+final...
++++}
}|code-block|syntax|javascript|1236253|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/7/docs/api/java/lang/SafeVarargs.html^0|E|C|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

You can add <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/SafeVarargs.html" rel="nofollow">@SafeVarargs</a> to method since Java 7, and you don't have to annotate on client code.

<pre><code>class Assembler&lt;X, Y&gt; {

 @SafeVarargs
 final void assemble(X container, Y... args) {
 //has to be final...
 }
}
</code></pre>

This is a simplified version of the code in question, one generic class uses another class with generic type parameters and needs to pass one of the generic types to a method with varargs parameters:

<pre><code>class Assembler&lt;X, Y&gt; {
 void assemble(X container, Y... args) { ... }
}

class Component&lt;T&gt; {
 void useAssembler(T something) {

 Assembler&lt;String, T&gt; assembler = new Assembler&lt;String, T&gt;();

 //generates warning:
 // Type safety : A generic array of T is
 // created for a varargs parameter
 assembler.assemble("hello", something);
 }
</code></pre>

}

Is there any correct way to pass along the generic parameter to a varargs method without encountering this warning?

Of course something like 

<pre><code>assembler.assemble("hello", new T[] { something });
</code></pre>

does not work since you cannot create generic arrays.

Is it possible to solve the "A generic array of T is created for a varargs parameter" compiler warning?

编译器

Java

这是相关代码的简化版本，一个泛型类使用另一个具有泛型类型参数的类，并且需要将其中一个泛型类型传递给具有varargs参数的方法：class Assembler<X, Y> { void assemble(X container, Y... args) { ... }}class Component<T> { ...

问有没有可能解决“为varargs参数创建T的泛型数组”的编译器警告？
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问有没有可能解决“为varargs参数创建T的泛型数组”的编译器警告？EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问有没有可能解决“为varargs参数创建T的泛型数组”的编译器警告？
EN