intstream.mapToObj()
时间: 2024-01-30 14:11:40 浏览: 25
IntStream的mapToObj()方法用于将IntStream中的每个元素映射为一个对象,并返回一个由这些对象组成的新流。这个方法可以用于将基本类型流转换为对象流。
以下是一个示例代码演示了mapToObj()方法的使用:
```java
IntStream intStream = IntStream.range(1, 5);
Stream<String> stringStream = intStream.mapToObj(i -> "Number " + i);
stringStream.forEach(System.out::println);
```
输出结果为:
```
Number 1
Number 2
Number 3
Number 4
```
在这个例子中,我们首先创建了一个IntStream,其中包含了1到4的整数。然后使用mapToObj()方法将每个整数映射为一个字符串,添加前缀"Number "。最后,我们使用forEach()方法打印出每个映射后的字符串。
相关问题
List<String> nameList = new ArrayList<>(); List<Entity> rsList = new ArrayList<>(); List<List<String>> valueList = new ArrayList<>(); for (Entity e : rsList) { List<String> singleRecord = new ArrayList<>(); nameList.forEach(n -> singleRecord.add(e.get(n) == null ? "" : e.get(n).toString())); if (e.getMetadata().containsKey(ChargeConst.RATE_RULE_DETAIL)) { Set<Map<String, Object>> ruleDtls = (Set<Map<String, Object>>) e.getMetadata().get(ChargeConst.RATE_RULE_DETAIL); Map<String, Object> mergedMap = ruleDtls.stream().flatMap(map -> map.entrySet().stream()) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (oldValue, newValue) -> newValue)); singleRecord = IntStream.range(0, singleRecord.size()) .mapToObj(i -> singleRecord.get(i).equals("") && mergedMap.get(nameList.get(i)) != null ? mergedMap.get(nameList.get(i)).toString() : singleRecord.get(i)) .collect(Collectors.toList()); } valueList.add(singleRecord); } if (e.getMetadata().containsKey(ChargeConst.RATE_RULE_DETAIL)) { Set<Map<String, Object>> ruleDtls = (Set<Map<String, Object>>) e.getMetadata().get(ChargeConst.RATE_RULE_DETAIL); Map<String, Object> mergedMap = ruleDtls.stream().flatMap(map -> map.entrySet().stream()) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (oldValue, newValue) -> newValue)); System.err.println(); } 错误:Local variable singleRecord defined in an enclosing scope must be final or effectively final
这个错误是因为在lambda表达式中使用了`singleRecord`这个变量,而且它不是final或者effective final的。为了解决这个问题,你可以将`singleRecord`声明为final,或者使用一个新的列表来存储在lambda表达式中需要使用的值,而不是直接引用`singleRecord`。例如:
```
final List<String> finalSingleRecord = singleRecord;
valueList.add(IntStream.range(0, finalSingleRecord.size())
.mapToObj(i -> finalSingleRecord.get(i).equals("") && mergedMap.get(nameList.get(i)) != null ? mergedMap.get(nameList.get(i)).toString() : finalSingleRecord.get(i))
.collect(Collectors.toList()));
```
或者
```
List<String> newSingleRecord = IntStream.range(0, singleRecord.size())
.mapToObj(i -> singleRecord.get(i).equals("") && mergedMap.get(nameList.get(i)) != null ? mergedMap.get(nameList.get(i)).toString() : singleRecord.get(i))
.collect(Collectors.toList());
valueList.add(newSingleRecord);
```
for (Entity e : rsList) { List<String> singleRecord = new ArrayList<>(); nameList.forEach(n -> singleRecord.add(e.get(n) == null ? "" : e.get(n).toString())); if (e.getMetadata().containsKey(ChargeConst.RATE_RULE_DETAIL)) { Set<Map<String, Object>> ruleDtls = (Set<Map<String, Object>>) e.getMetadata().get(ChargeConst.RATE_RULE_DETAIL); Map<Object, Object> mergedMap = ruleDtls.stream() .flatMap(map -> map.entrySet().stream().map(entry -> new AbstractMap.SimpleEntry<>(entry.getKey(), entry.getValue() == null ? "" : entry.getValue()))) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (oldValue, newValue) -> newValue)); final List<String> finalSingleRecord = singleRecord; valueList.add(IntStream.range(0, finalSingleRecord.size()).mapToObj( i -> finalSingleRecord.get(i).equals("") && mergedMap.get(nameList.get(i)) != null ? mergedMap.get(nameList.get(i)).toString() : finalSingleRecord.get(i)) .collect(Collectors.toList())); continue; } valueList.add(singleRecord); }降低代码复杂度
可以将代码分解为多个方法来降低复杂度,例如:
1. 提取一个方法来处理每个实体记录,将其转换为一个 String 类型的 List。
```
private List<String> processEntity(Entity e, List<String> nameList) {
List<String> singleRecord = new ArrayList<>();
nameList.forEach(n -> singleRecord.add(e.get(n) == null ? "" : e.get(n).toString()));
if (e.getMetadata().containsKey(ChargeConst.RATE_RULE_DETAIL)) {
Set<Map<String, Object>> ruleDtls = (Set<Map<String, Object>>) e.getMetadata().get(ChargeConst.RATE_RULE_DETAIL);
Map<Object, Object> mergedMap = mergeRuleDetails(ruleDtls);
final List<String> finalSingleRecord = singleRecord;
return IntStream.range(0, finalSingleRecord.size())
.mapToObj(i -> finalSingleRecord.get(i).equals("") && mergedMap.get(nameList.get(i)) != null ? mergedMap.get(nameList.get(i)).toString() : finalSingleRecord.get(i))
.collect(Collectors.toList());
}
return singleRecord;
}
```
2. 提取一个方法来合并所有规则细节的 Map。
```
private Map<Object, Object> mergeRuleDetails(Set<Map<String, Object>> ruleDtls) {
return ruleDtls.stream()
.flatMap(map -> map.entrySet().stream()
.map(entry -> new AbstractMap.SimpleEntry<>(entry.getKey(), entry.getValue() == null ? "" : entry.getValue())))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (oldValue, newValue) -> newValue));
}
```
3. 将原来的主方法进行简化,使用上面的两个方法来处理每个实体记录,并将结果添加到 valueList 中。
```
for (Entity e : rsList) {
List<String> singleRecord = processEntity(e, nameList);
valueList.add(singleRecord);
}
```