让我们介绍一下课程NutritionAccumulator：
class NutritionAccumulator{
private double fat = 0.;
private double carbs = 0.;
private double fiber = 0.;
private double protein = 0.;
public NutritionAccumulator() {
}
public NutritionAccumulator(double fat, double carbs, double fiber, double protein) {
this.fat = fat;
this.carbs = carbs;
this.fiber = fiber;
this.protein = protein;
}
public NutritionAccumulator add(NutritionAccumulator that){
return new NutritionAccumulator(this.fat + that.fat,
this.carbs + that.carbs,
this.fiber + that.fiber,
this.protein + that.protein
);
}
}
现在我们可以编写简单的stream reduce：
Optional.ofNullable(response.body())
.stream()
.reduce(
new NutritionAccumulator(),
(acc, fudNut) -> new NutritionAccumulator(
fudNut.getTotalFat(),
fudNut.getTotalCarbohydrate(),
fudNut.getDietaryFiber(),
fudNut.getProtein()
).add(acc),
NutritionAccumulator::add
);
最后，您可以将结果从上方传递给生成器。
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