[英]Using mutable objects as keys in HashMaps
I have a digraph data structure which uses list representation( HashMap<Vertex, ArrayList<Vertex>>
); 我有一个使用列表表示的有向图数据结构( HashMap<Vertex, ArrayList<Vertex>>
); source vertex as the key and an ArrayList of destination vertices as the value. 源顶点作为键,目标顶点的ArrayList作为值。 A depth first search and dfs loop are used to traverse the graph to find the execution order of the vertices. 深度优先搜索和dfs循环用于遍历图以找到顶点的执行顺序。
The execution order is set as a label of a Vertex object by setLabel(int i)
and only the String name
field is used to generate hashcode
. 通过setLabel(int i)
将执行顺序设置为Vertex对象的标签,并且仅将String name
字段用于生成hashcode
。
My problem is that after dfs
is completed and when I iterate through the keys of the HashMap [ graph.keySet()
] , there are still few Vertices which are not labeled, But when I iterate though the explored set which is a HashSet<Vertex>
, all the possible vertices are labeled(Accurately). 我的问题是在完成dfs
之后,当我遍历HashMap [ graph.keySet()
]的键时, 仍然有一些顶点没有被标记,但是当我遍历所探索的集合(即HashSet<Vertex>
,所有可能的顶点都被标记(准确)。
What could possibly be happening here? 这里可能会发生什么? (I can only use the HashMap to retrieve the labels of the vertices) (我只能使用HashMap来检索顶点的标签)
Note: I believe this is relevant to using mutable objects as keys in HashMaps. 注意:我相信这与在HashMaps中使用可变对象作为键有关。 If not please correct me. 如果没有,请纠正我。
/**
* Recursive depth-first search
* @param graph HashMap<Vertex,ArrayList> (list representation)
* @param start starting Vertex
*/
public void dfsR(HashMap<Vertex, ArrayList<Vertex>> graph, Vertex start) {
this.explored.add(start); //a HashSet<Vertex>
ArrayList<Vertex> list = graph.get(start);
if (list != null) {
for (Vertex v : list) {
if (!this.explored.contains(v)) {
this.dfsR(graph, v);
}
}
}
/* First pass-Execution order */
if (!this.secondPass) {
start.setLabel(++this.label);
}
}
/**
* Run DFS on every vertex of the Graph
* @param graph HashMap<Vertex,ArrayList<Vertex>> (list representation)
*/
private void dfsLoop(HashMap<Vertex, ArrayList> graph) {
this.secondPass = false;
this.explored.clear();
this.label = 0;
for (Vertex vertex : graph.keySet()) {
if (!this.explored.contains(vertex)) {
this.dfsR(graph, vertex); /* Recursive dfs */
}
}
}
public class Vertex {
private final String name;
private int label;
public Vertex(String name) {
this.name = name;
this.label = -1;
}
public Vertex(Integer name) {
this.name = String.valueOf(name);
this.label = -1;
}
public String getName() {
return name;
}
/**
* Value(Label) obtained from Topological Ordering
* @param label integer value of the relevant position
*/
public void setLabel(int label){
this.label = label;
}
/**
* @return the Label obtained from the Topological ordering
*/
public int getLabel(){
return this.label ;
}
@Override
public String toString() {
return name;
}
@Override
public boolean equals(Object o) {
if(o == null){
return false;
}
if (o instanceof Vertex) {
Vertex v = (Vertex) o;
return this.name.equals(v.getName());
}
return false;
}
@Override
public int hashCode() {
int hash = 3;
hash = 89 * hash + this.name.hashCode();
return hash;
}}
The problem is almost certainly related to the management of the secondPass
variable, as that is what controls whether or not to set the label: 这个问题几乎可以肯定与secondPass
变量的管理有关,因为这是控制是否设置标签的原因:
if (!this.secondPass) {
start.setLabel(++this.label);
}
The code you provided does not show where this would be set to true. 您提供的代码未显示将其设置为true的位置。
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