[英]Sorting HashMap into TreeMap: custom Comparator removes values with the same key
我正在嘗試對HashMap<String, Long>
進行排序。 我有以下代碼進行排序:
private static class ValueComparator implements Comparator<String>{
HashMap<String, Long> map = new HashMap<String, Long>();
public ValueComparator(HashMap<String, Long> map){
this.map.putAll(map);
}
@Override
public int compare(String s1, String s2) {
if(map.get(s1) > map.get(s2)){
System.out.println("s1: " + s1 + "; s2: " + s2);
return -1;
}
else if (map.get(s1).equals(map.get(s2))) {
return 0;
}
else{
return 1;
}
}
}
private static TreeMap<String, Long> sortMapByValue(HashMap<String, Long> map){
Comparator<String> comparator = new ValueComparator(map);
//TreeMap is a map sorted by its keys.
//The comparator is used to sort the TreeMap by keys.
TreeMap<String, Long> result = new TreeMap<String, Long>(comparator);
result.putAll(map);
System.out.println("DONE sort");
return result;
}
問題是,當幾個不同的鍵具有相同的值時,只有一個鍵會使其進入最終映射:
例:
public class Test {
public static void main(String[] args) {
HashMap<String, Long> hashMap = new HashMap<>();
hashMap.put("Cat", (long) 4);
hashMap.put("Human", (long) 2);
hashMap.put("Dog", (long) 4);
hashMap.put("Fish", (long) 0);
hashMap.put("Tree", (long) 1);
hashMap.put("Three-legged-human", (long) 3);
hashMap.put("Monkey", (long) 2);
System.out.println(hashMap); //7 pairs
System.out.println(sortMapByValue(hashMap)); //5 pairs
}
}
我該如何解決?
我認為您以意想不到的方式使用地圖並違反合同是無法修復的。 樹圖期望按鍵排序,並且鍵應唯一,因此當compare == 0時,它將僅覆蓋節點的值。 您始終可以實現自己的TreeMap並使其隨心所欲。
我不確定您要怎么做,但我認為您需要
TreeMap<Long,List<String>>
http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/share/classes/java/util/TreeMap.java
if (cpr != null) {
do {
parent = t;
cmp = cpr.compare(key, t.key);
if (cmp < 0)
t = t.left;
else if (cmp > 0)
t = t.right;
else
return t.setValue(value);
} while (t != null);
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