Set values are getting updated in all the list variables

Question

I have a complex structure like

ArrayList<LinkedList<Struct>>

In my main class I have 2 nested classes as below

  static class struct {

            private String name;
            Set<String> rights = new HashSet<String>();
//getters and setters
    }
    static class Graph {
            ArrayList<LinkedList<struct>> adjListArray;

            Graph() {
                adjListArray = new ArrayList<>();
            }
        }

addEdge function

    static void addEdge(Graph graph, String src, String dest, Set<String> rights) {
// code for creating a src block if it is not present and adding dest to it as below
    struct destStruct = new struct();
            destStruct.setName(dest);
            destStruct.setRights(rights);
            graph.adjListArray.get(getIndexOf(graph, src)).add(destStruct); // getIndexof is a function which will return the list index whose first element name is equal to src
    }

I am passing these values from main function

public static void main(String args[]) {
        Graph graph = new Graph();
        Set<String> rights = new HashSet<String>();
        rights.add("T");
        rights.add("G");
        addEdge(graph, "A", "V", rights);
        rights.clear();
        rights.add("G");
        addEdge(graph, "B", "V", rights);
        printGraph(graph);
}

printGraph function

static void printGraph(Graph graph) {
        for (LinkedList<struct> list : graph.adjListArray) {
            for (struct var : list) {
                System.out.println(
                        "src=" + list.get(0).getName() + " dest=" + var.getName() + " rights=" + var.getRights());
            }
            System.out.println("\n");
        }
    }

The output is

src=A dest=A rights=[]
src=A dest=V rights=[G]


src=B dest=B rights=[]
src=B dest=V rights=[G]

but expected output is

src=A dest=A rights=[]
src=A dest=V rights=[T, G]


src=B dest=B rights=[]
src=B dest=V rights=[G]

I couldn't understand why rights of edge (A,V) got updated with the rights of rights of (B,V). When I send only (A,V) from main I am getting the values correctly as

src=A dest=A rights=[]
src=A dest=V rights=[T, G]

Wanted to understand why this is happening and how to resolve this?

Please show the code in `printGraph(graph);` – FailingCoder Nov 17 '19 at 05:20 — FailingCoder, Nov 17 '19 at 05:20
printGraph function is also added – sreenivas Nov 17 '19 at 05:25 — sreenivas, Nov 17 '19 at 05:25

Somil Garg · Accepted Answer · 2019-11-17T05:41:12.937

List.clear()

clear() will go through the underlying Array and set each entry to null.

using rights.clear() You have removed the reference pointing to :-

rights.add("T");        
rights.add("G");

in graph you have to create a new copy of rights for your changes to show otherwise using clear() will remove all the existing references from the memory.

update the addEdge method:-

static void addEdge(Graph graph, String src, String dest, Set<String> rights) {
           Set<String> copyRights = new HashSet<>(rights); //create a new copy of rights.
            struct destStruct = new struct();
                    destStruct.setName(dest);
                    destStruct.setRights(copyRights);
                    graph.adjListArray.get(getIndexOf(graph, src)).add(destStruct); // getIndexof is a function which will return the list index whose first element name is equal to src
}

https://stackoverflow.com/q/40480/4007703 read this for a better understanding. — Somil Garg, Nov 17 '19 at 05:35

Set values are getting updated in all the list variables

1 Answers1