无法将 void 转换为 java.lang.Void
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Cannot convert void to java.lang.Void
提问by Kastaneda
I'm trying to do the following
我正在尝试执行以下操作
interface Updater {
void update(String value);
}
void update(Collection<String> values, Updater updater) {
update(values, updater::update, 0);
}
void update(Collection<String> values, Function<String, Void> fn, int ignored) {
// some code
}
but I get this compiler error:
但我收到此编译器错误：
"Cannot convert void to java.lang.Void"
That means updater::updatecannot be used as Function<String, Void>.
这意味着updater::update不能用作Function<String, Void>.
Of course I can't write Function <String, void>and I don't want to change return type of update()to Void.
当然，我不能写Function <String, void>，我不想改变返回类型update()来Void。
How do I resolve this problem?
我该如何解决这个问题？
回答by Holger
A Functionreturns a value, even if it is declared as being of type Void(you will have to return nullthen. In contrast, a voidmethod really returns nothing, not even null. So you have to insert the returnstatement:
AFunction返回一个值，即使它被声明为类型Void（你将不得不返回null。相反，一个void方法实际上什么都不返回，甚至不返回null。所以你必须插入return语句：
void update(Collection<String> values, Updater updater) {
update(values, s -> { updater.update(); return null; }, 0);
}
An alternative would be to change the Function<String,Void>to Consumer<String>, then you can use the method reference:
另一种方法是将 更改Function<String,Void>为Consumer<String>，然后您可以使用方法引用：
void update(Collection<String> values, Updater updater) {
update(values, updater::update, 0);
}
void update(Collection<String> values, Consumer<String> fn, int ignored) {
// some code
}
回答by Hoopje
A function returns a value. What you are looking for is the java.util.function.Consumerinterface. This has an void accept(T)method and doesn't return a value.
函数返回一个值。您正在寻找的是java.util.function.Consumer界面。这有一个void accept(T)方法并且不返回值。
So you method becomes:
所以你的方法变成：
void update(Collection<String> values, Consumer<String> fn, int ignored) {
// some code
}
