如何在Java中读取MultiValue ArrayList

Question

我定义了一个arrayList如下

​

    List<List<RiskyPersons>> dataArray = new ArrayList<>();

​

这是RiskyPersons类

​

public class RiskyPersons {
    private SA3Tenant sa3tenant;
    private int NumberofPersonInCategory;
    
    public RiskyPersons(){
    }

    public RiskyPersons(SA3Tenant sa3tenant, int NumberofPersonInCategory) {
        this.sa3tenant = sa3tenant;
        this.NumberofPersonInCategory = NumberofPersonInCategory;
    }
}

​

然后，我成功地添加了数据并保存在dataArray ArrayList中。下面的输出显示了使用SOP(DataArray)保存的ArrayList；

​

[[RiskyPersons{sa3tenant=Homeless.SA3Tenant@3a7cc6b0, NumberofPersonInCategory=99}]]

​

我想分别阅读这个dataArray ArrayList和 ArrayList。如何访问"NumberofPersonInCategory“值？

Answer 1

你需要把它迭代两倍

for (List<RiskyPersons> rp : dataArray) {
for (RiskyPersons o : rp) {
    System.out.println(o.NumberofPersonInCategory); // unrelated : but its bad naming convention
}
}

Answer 2

来自Java-8及以上的用户可以使用流。

dataArray.stream()
    .flatMap(List::stream)
    .map(RiskyPersons::NumberofPersonInCategory)
    .forEach(System.out::println)

Answer 3

我希望这能帮到你！

public class RiskyPersons {
    private SA3Tenant sa3tenant;
    private int NumberofPersonInCategory;

    public int getNumberofPersonInCategory() {
        return NumberofPersonInCategory;
    }

    public RiskyPersons(){
    }

    public RiskyPersons(SA3Tenant sa3tenant, int NumberofPersonInCategory) {
        this.sa3tenant = sa3tenant;
        this.NumberofPersonInCategory = NumberofPersonInCategory;
    }
}


List<Integer> values = dataArray.parallelStream().flatMap(Collection::stream).map(RiskyPersons::getNumberofPersonInCategory)
                .collect(Collectors.toCollection(ArrayList::new));