Lambda表示式排序，出現空指標異常

問題描述：物件集合中，根據物件的某個屬性進行公升降排序時，未考慮對應屬性的null值，導致出現空指標異常。

解決方法：comparator.nullsfirst和comparator.nullslast

listnlist = list.stream().sorted(

comparator.comparing(user::getcode, comparator.nullsfirst(string::compareto)))
.collect(collectors.tolist());

/**

* returns a null-friendly comparator that considers  to be
* less than non-null. when both are , they are considered
* equal. if both are non-null, the specified  is used
* to determine the order. if the specified comparator is ,
* then the returned comparator considers all non-null values to be equal.
** the returned comparator is serializable if the specified comparator
* is serializable.
** @param  the type of the elements to be compared
* @param  comparator a  for comparing non-null values
* @return a comparator that considers  to be less than
*         non-null, and compares non-null objects with the supplied
*         .
* @since 1.8
*/public static comparatornullsfirst(comparator<? super t> comparator) 
/*** null-friendly comparators
*/final static class nullcomparatorimplements comparator, serializable 
@override
public int compare(t a, t b)  else if (b == null)  else 
}@override
public comparatorthencomparing(comparator<? super t> other) 
@override
public comparatorreversed() 
}

lambda表示式排序出現空指標

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Lambda表示式排序，出現空指標異常

問題描述 物件集合中，根據物件的某個屬性進行公升降排序時，未考慮對應屬性的null值，導致出現空指標異常。解決方法 comparator.nullsfirst和comparator.nullslast listnlist list.stream sorted comparator.comparing...

Lambda表示式排序，解決空指標異常

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