在Java 8 Stream中解决没有最终变量 [英] Solve no final variable inside Java 8 Stream

问题描述

是否有办法将以下代码转换为Java 8 Stream。

Is there is a way to convert the following code to Java 8 Stream.

    final List ret = new ArrayList(values.size());
    double tmp = startPrice;
    for (final Iterator it = values.iterator(); it.hasNext();) {
      final DiscountValue discountValue = ((DiscountValue) it.next()).apply(quantity, tmp, digits, currencyIsoCode);
      tmp -= discountValue.getAppliedValue();
      ret.add(discountValue);
    }

Java 8流抱怨没有最终变量tmp？有办法解决这种情况吗？

Java 8 streams complains about no final variable tmp ? Is there a way to solve such situations ?

在封闭范围内定义的局部变量tmp必须是最终的或有效的最终

Local variable tmp defined in an enclosing scope must be final or effectively final

推荐答案

首先，将代码更改为使用泛型，并使用增强的更改循环。假设值是 List< DiscountValue> ，这就是你得到的：

First, change the code to use generics and an enhanced for loop. Assuming values is then a List<DiscountValue>, this is what you get:

List<DiscountValue> ret = new ArrayList<>(values.size());
double tmp = startPrice;
for (DiscountValue value : values) {
    DiscountValue discountValue = value.apply(quantity, tmp, digits, currencyIsoCode);
    tmp -= discountValue.getAppliedValue();
    ret.add(discountValue);
}

我建议坚持下去，而不是将其转换为流，但是如果你坚持，你可以使用单元素数组作为价值持有者。

I'd suggest staying with that, and not convert it to streams, but if you insist, you can use a one-element array as a value-holder.

注意 ret 和 tmp 不必声明 final ，只要它们是有效最终的。

Note that ret and tmp doesn't have to be declared final, as long as they are effectively-final.

List<DiscountValue> ret = new ArrayList<>(values.size());
double[] tmp = { startPrice };
values.stream().forEachOrdered(v -> {
    DiscountValue discountValue = v.apply(quantity, tmp[0], digits, currencyIsoCode);
    tmp[0] -= discountValue.getAppliedValue();
    ret.add(discountValue);
});

如你所见，你没有通过使用流获得任何东西。代码实际上更糟，所以...... 不。

As you can see, you haven't gained anything by using streams. The code is actually worse, so ... don't.

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