如何读取 Java 中的多值 ArrayList

Question

我定义了一个 arrayList 如下

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

这里是 RiskyPersons Class

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

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

那么我已经成功添加数据并保存在dataArray ArrayList中。以下输出显示使用 SOP(dataArray);

保存的 ArrayList

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

我想读取这个 dataArray ArrayList 并分别显示值。如何访问 "NumberofPersonInCategory" 值？

Answer 1

您需要将其迭代两次

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

Answer 2

从Java-8及以上可以使用stream:

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

Answer 3

希望对您有所帮助！

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));

如何读取 Java 中的多值 ArrayList

How to read MultiValue ArrayList in Java

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