英文:
Java HashMap take out keys based on value
问题
这是我的哈希映射（Hashmap），其中键是一个名为Payment的模型，值是一个String，表示支付过程中发生的错误。
Map<Payment, String> mapPaymentWithError = new HashMap<>()
如果支付没有错误，我们将字符串值存储为null，并将Payment模型数据作为键。
我正在尝试基于上述哈希映射中错误String是否为Null或NotNull来对Payment进行分组，该哈希映射包含许多记录。
如下所示：
List<Payment> withNullErrors = .............. // 具有null字符串值 List<Payment> withErrors = ................... // 具有NotNull字符串值
如何实现这一点？
尝试使用Collectors.GroupingBy和其他方法，但未能成功。
英文:
This is my Hashmap in which the key is a model Payment and value is a String, which is an Error occurred during payment.
Map<Payment, String> mapPaymentWithError = new HashMap<>()
If there are no errors in Payment we are storing String value as null and the key as Payment model data.
I am trying to group Payment based on whether error String was Null or NotNull from above HashMap which is having many records.
Like below
List<Payment> withNullErrors = .............. // having String value as Null
List<Payment> withErrors = ................... // having String value as NotNull
How to do this ?
Tried using Collectors.GroupingBy and other ways but its not working
答案1
得分: 1
以下是您要翻译的代码部分：
public class ListFiltering {
public static void main( String[] args ) {
Map<Payment, String> mapPaymentWithError = new HashMap<>();
mapPaymentWithError.put( new Payment( "1" ), "1" );
mapPaymentWithError.put( new Payment( "null" ), null );
List<Payment> withNullErrors = mapPaymentWithError.entrySet().stream()
.filter( e -> e.getValue() == null )
.map( e -> e.getKey() )
.toList();
List<Payment> withErrors = mapPaymentWithError.entrySet().stream()
.filter( e -> e.getValue() != null )
.map( e -> e.getKey() )
.toList();
System.out.println( "with null errors: " + withNullErrors );
System.out.println( "with other errors: " + withErrors );
}
static record Payment( String id ) {}
}
英文:
Do you mean something like this?
public class ListFiltering {
public static void main( String[] args ) {
Map<Payment, String> mapPaymentWithError = new HashMap<>();
mapPaymentWithError.put( new Payment( "1" ), "1" );
mapPaymentWithError.put( new Payment( "null" ), null );
List<Payment> withNullErrors = mapPaymentWithError.entrySet().stream()
.filter( e -> e.getValue() == null )
.map( e -> e.getKey() )
.toList();
List<Payment> withErrors = mapPaymentWithError.entrySet().stream()
.filter( e -> e.getValue() != null )
.map( e -> e.getKey() )
.toList();
System.out.println( "with null errors: " + withNullErrors );
System.out.println( "with other errors: " + withErrors );
}
static record Payment( String id ) {}
}
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