java比较器、集合和哈希映射
我之前需要根据HashMap的值对其进行排序,并将comparator与集合一起使用,如下所示:
private LinkedHashMap<String, Integer> sortMap(Map<String, Integer> results, int count)
{
List<Map.Entry<String, Integer>> entries = new ArrayList<Map.Entry<String, Integer>>(results.entrySet());
Comparator<Entry<String, Integer>> comparator = new Comparator<Entry<String, Integer>>() {
@Override
public int compare(Entry<String, Integer> a, Entry<String, Integer> b) {
return b.getValue().compareTo(a.getValue());
}
};
Collections.sort(entries, comparator);
LinkedHashMap<String, Integer> sorted = new LinkedHashMap<String, Integer>();
for (Entry<String, Integer> entry : entries)
sorted.put(entry.getKey(), entry.getValue());
return sorted;
}
现在情况变了,我需要它是一个已排序的HashMap。所以我把代码改成这样:
private LinkedHashMap<String, Double> sortMap(Map<String, Double> results, int count)
{
List<Map.Entry<String, Double>> entries = new ArrayList<Map.Entry<String, Double>>(results.entrySet());
Comparator<Entry<String, Double>> comparator = new Comparator<Entry<String, Double>>() {
@Override
public int compare(Entry<String, Double> a, Entry<String, Double> b) {
return b.getValue().compareTo(a.getValue());
}
};
Collections.sort(entries, comparator);
LinkedHashMap<String, Double> sorted = new LinkedHashMap<String, Double>();
for (Entry<String, Double> entry : entries)
sorted.put(entry.getKey(), entry.getValue());
return sorted;
}
它抛出一个错误,即java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Double
:
at myPackage.myClass$1.compare(myClass.java:124)
at myPackage.myClass$1.compare(myClass.java:1)
at java.util.TimSort.countRunAndMakeAscending(Unknown Source)
at java.util.TimSort.sort(Unknown Source)
at java.util.TimSort.sort(Unknown Source)
at java.util.Arrays.sort(Unknown Source)
at java.util.Collections.sort(Unknown Source)
at myPackage.myClass.sortMap(myClass.java:128)
我的班级。JAVA128:Collections.sort(entries, comparator);
我的班级。JAVA124:return b.getValue().compareTo(a.getValue());
非常感谢你们的帮助,谢谢
# 1 楼答案
你有两个选择:
将排序方法更改为获取
Integer
,而不是Double
将
entry.getValue()
的返回类型更改为Double# 2 楼答案
您将sortMap()方法的签名从Integer改为Double,但仍使用Integer调用它。使用树形图可能是进行隐式排序的一个选项吗