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125 天前 回复了 jawe001 创建的主题 › Java › 求 Java 大佬帮忙分析下这个程序 |
The incomparable types error is telling you that it doesn't make sense to compare two things that cannot possibly be equal.
For example, there's no point in Integer.valueOf(0) == "", because they're not the same types; nor is one a supertype of the other. It will always be false.
The compiler will prevent the a == b if both are class types (as opposed to interfaces), and both a = b and b = a would be disallowed.
So, you are being told that a Class<? extends T[]> cannot be equal to a Class<Object[]>, because you can't assign a reference of one type to a variable of the other type.
By casting one of the references to Object, the compiler no longer knows (/thinks) that the types are definitely not related - because Object is a supertype of everything, so "nor is one a supertype of the other" is no longer true - so the compiler allows the check.
One thing that is redundant in that method is U. There's no need for it, just use Object[] in the parameter type instead.
For example, there's no point in Integer.valueOf(0) == "", because they're not the same types; nor is one a supertype of the other. It will always be false.
The compiler will prevent the a == b if both are class types (as opposed to interfaces), and both a = b and b = a would be disallowed.
So, you are being told that a Class<? extends T[]> cannot be equal to a Class<Object[]>, because you can't assign a reference of one type to a variable of the other type.
By casting one of the references to Object, the compiler no longer knows (/thinks) that the types are definitely not related - because Object is a supertype of everything, so "nor is one a supertype of the other" is no longer true - so the compiler allows the check.
One thing that is redundant in that method is U. There's no need for it, just use Object[] in the parameter type instead.
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