Java流在列表内迭代列表并计算布尔值

Question

如何在列表的列表中计算布尔值?列表中的每个元素都有一个嵌套的列表。下面是代码片段

class ChildComponent {
List<ChildComponent> childComponents = new ArrayList<>();
Boolean notificationEnabled = Boolean.FALSE;
String name;
//respective Gettters/Setters
}
class ModelItem {
List<ChildComponent> components = new ArrayList<>();
Boolean alertUser;
}

ModelItem有一个list的分量。list组件中的每个组件都有一个notificationEnabled标志。此外，每个组件都有一个ChildComponent列表。

alertUser应设置为true在以下情况下:

• 如果components中的ChildComponent将notificationEnabled设置为true
• List<ChildComponent> childComponents中的任何元素都将notificationEnabled设置为true

基本上，如果任何Components将notificationEnabled设置为true那么alertUser应该设置为true

怎么做?

modelItem.components.stream().flatMap(a -> a.childComponents.stream())不工作，因为它检查。在代码片段

中查看更多细节下面是示例代码:

public static void main(String[] args) {
ModelItem modelItem1 = new ModelItem();
modelItem1.components.add(createC1());
modelItem1.components.add(createC2());
updateAlert(modelItem1);
}

**// does not work. It only check childComponents**
private static void updateAlert(ModelItem modelItem) {
boolean anyMatchFilterPromptAtRun = modelItem.components.stream().flatMap(a -> a.childComponents.stream())
.anyMatch(b -> b.notificationEnabled.equals(Boolean.TRUE));
modelItem.alertUser = Boolean.valueOf(anyMatchFilterPromptAtRun);
}
private static ChildComponent createC1() {
ChildComponent c1_1 = new ChildComponent();
c1_1.name = "c1_1";
c1_1.notificationEnabled = false;
ChildComponent c1_2 = new ChildComponent();
c1_2.name = "c1_2";
c1_2.notificationEnabled = true;
// main C2
ChildComponent c1 = new ChildComponent();
c1.name = "C1";
c1.childComponents = Arrays.asList(c1_1, c1_2) ;
c1.notificationEnabled = false;
return c1;
}

private static ChildComponent createC2() {
ChildComponent c1_1 = new ChildComponent();
c1_1.name = "c1_1";
c1_1.notificationEnabled = false;
ChildComponent c1_2 = new ChildComponent();
c1_2.name = "c1_2";
c1_2.notificationEnabled = true;
// main C1
ChildComponent c1 = new ChildComponent();
c1.name = "C1";
c1.childComponents = Arrays.asList(c1_1, c1_2) ;
c1.notificationEnabled = false;
return c1;
}

下面是示例结构

{
"components": [
{
"name": "C1",
"notificationEnabled": false,
"childComponents": [
{
"name": "c1_1",
"notificationEnabled": false,
"childComponents": []
},
{
"name": "c1_2",
"notificationEnabled": true,
"childComponents": []
}
]
},
{
"name": "C1",
"notificationEnabled": false,
"childComponents": [
{
"name": "c1_1",
"notificationEnabled": false,
"childComponents": []
},
{
"name": "c1_2",
"notificationEnabled": true,
"childComponents": []
}
]
}
]
}

Answer 1

听起来您需要递归地遍历组件的层次结构。你可以这样做:

Stream<ChildComponent> recursiveWalk(List<ChildComponent> list) {
if (list.isEmpty())
return Stream.empty();
}

return Stream.concat(list.stream(),
recursiveWalk(list.stream()
.map(ChildComponent::childComponents)
.flatMap(Collection::stream)
.collect(toList())));
}
alertUser = recursiveWalk(components).anyMatch(ChildComponent::notificationEnabled);

Answer 2

如果你把深度搜索放在正确的位置，一切都很容易。这里正确的类是ChildComponent。

public class ChildComponent {
List<ChildComponent> childComponents = new ArrayList<>();
String name;
boolean notificationEnabled;
/** Deep search */
public boolean isNotificationEnabled() {
return notificationEnabled || childComponents.stream()
.filter(ChildComponent::isNotificationEnabled).findFirst().isPresent();
}
}