没有为带有 Comparator<Map.Entry 的 TreeMap 找到合适的构造函数

Question

我想创建一个 TreeMap 和一个匿名 class 比较器来比较值。但是，我得到一个错误。我哪里错了？

private List<Map<Integer,Integer>> edges;
/*
*   init edges database
*/
private void initEdges() {
    edges = new ArrayList<Map<Integer,Integer>>();
    for(int i = 0; i < this.amountOfVertices; i++) {
        edges.add(
                new TreeMap<Integer, Integer>(
                        new Comparator<Map.Entry<Integer, Integer>>() {
                            @Override
                            public int compare(Map.Entry<Integer, Integer> i1, Map.Entry<Integer, Integer> i2)
                            {
                                int res = i1.getValue().compareTo(i2.getValue());
                                return res != 0 ? res : 1;
                            }
                        }
                )
        );
    }
}

确切错误是

Error:(21, 21) java: no suitable constructor found for TreeMap(<anonymous java.util.Comparator<java.util.Map.Entry<java.lang.Integer,java.lang.Integer>>>)
    constructor java.util.TreeMap.TreeMap(java.util.Comparator<? super java.lang.Integer>) is not applicable
      (argument mismatch; <anonymous java.util.Comparator<java.util.Map.Entry<java.lang.Integer,java.lang.Integer>>> cannot be converted to java.util.Comparator<? super java.lang.Integer>)
    constructor java.util.TreeMap.TreeMap(java.util.Map<? extends java.lang.Integer,? extends java.lang.Integer>) is not applicable
      (argument mismatch; <anonymous java.util.Comparator<java.util.Map.Entry<java.lang.Integer,java.lang.Integer>>> cannot be converted to java.util.Map<? extends java.lang.Integer,? extends java.lang.Integer>)
    constructor java.util.TreeMap.TreeMap(java.util.SortedMap<java.lang.Integer,? extends java.lang.Integer>) is not applicable
      (argument mismatch; <anonymous java.util.Comparator<java.util.Map.Entry<java.lang.Integer,java.lang.Integer>>> cannot be converted to java.util.SortedMap<java.lang.Integer,? extends java.lang.Integer>)

Answer 1

我认为你给 TreeMap<Integer,Integer> 的比较器应该知道如何比较 Integer，而不是 Map.Entry 对象。

Answer 2

A TreeMap 按其键（而非条目）排序。你需要这样的东西，

edges.add(new TreeMap<Integer, Integer>(new Comparator<Integer>() {
    @Override
    public int compare(Integer o1, Integer o2) {
        return o1.compareTo(o2);
    }
}));

没有为带有 Comparator<Map.Entry 的 TreeMap 找到合适的构造函数

No suitable constructor found for TreeMap with Comparator<Map.Entry

java

generics

comparator