CODEWITHSUNDEEP
javajava-8java-stream
Saurabh Kumar
Saurabh Kumar

Reputation: 16661

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

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

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Upvotes: 3

Views: 4270

Answers (2)

swyrik
swyrik

Reputation: 314

Use an AtomicReference variable.

AtomicReference<Double> temp = new AtomicReference<>();
temp.set(356.65);

Double[] values = {23.4, 45.6,9.4,1.43};

Stream.of(values).forEach(val -> {
          temp.set(temp.get() - val);
});

System.out.println(temp.get());

Output

"C:\Program Files\Java\jdk1.8.0_261\bin\java.exe...
276.82

Process finished with exit code 0

Upvotes: 0

Andreas
Andreas

Reputation: 159096

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);
}

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.

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);
});

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

Upvotes: 8

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