打印低于阈值的动物总数

Question

我正在尝试解决书中的一个练习：Objects first with Java：使用 BlueJ 的实用介绍。

练习如下：

Exercise 5.17 Rewrite the printEndangered method in your project to use Streams.

原代码为：

public void printEndangered(ArrayList<String> animalNames, int dangerThreshold)
{
    for(String animal : animalNames) {
        if(getCount(animal) <= dangerThreshold) {
            System.out.println(animal + " is endangered.");
        }
    }
}

我的尝试是这样的：

sightings.stream()
    .filter(s -> animalNames.equals(s.getAnimal()))
    .filter(s -> s.getCount() <= dangerThreshold)
    .mapToInt(s -> s.getCount())
    .forEach(s -> System.out.println(s));

Answer 1

getCount()方法属于包含printEndangered的class，不属于s：

public void printEndangered(ArrayList<String> animalNames, int dangerThreshold) {
    animalNames.stream()
               .filter(animal -> getCount(animal) <= dangerThreshold)
               .map(animal -> animal + " is endangered.")
               .forEach(System.out::println);
}

Answer 2

sightings.stream()
//.filter(s -> animalNames.equals(s.getAnimal())) -- not required
.filter(s -> getCount(s) <= dangerThreshold)
//.mapToInt(s -> s.getCount()) -- not required
.forEach(s -> System.out.println(s + " is Endangered"));

打印低于阈值的动物总数

Printing the sum of animals that are below a threshold

java

lambda

functional-programming

bluej

java-stream