Error when changing method argument from String to int

Question

I used this example code: https://github.com/jgrapht/jgrapht/wiki/DirectedGraphDemo to create a digraph. In this example, the Digraph is created with vertices that are Strings. I need vertices to be points, which I designate with an iD in my code (iDs are going from 0 to 3 so these are int). So I modified the example to do this:

public class DirectedGraphDemo {
    public static void graph(int ... iD) {
        // constructs a directed graph with the specified vertices and edges
        DirectedGraph<int, DefaultEdge> directedGraph =
            new DefaultDirectedGraph<int, DefaultEdge>
            (DefaultEdge.class);
        directedGraph.addVertex(0);
        directedGraph.addVertex(1);
        directedGraph.addVertex(2);
        directedGraph.addVertex(3);

        directedGraph.addEdge(0,1);
        directedGraph.addEdge(1,2);
        directedGraph.addEdge(2,3);

        // computes all the strongly connected components of the directed graph
        StrongConnectivityInspector sci =
            new StrongConnectivityInspector(directedGraph);
        List stronglyConnectedSubgraphs = sci.stronglyConnectedSubgraphs();

        // prints the strongly connected components
        System.out.println("Strongly connected components:");
        for (int i = 0; i < stronglyConnectedSubgraphs.size(); i++) {
            System.out.println(stronglyConnectedSubgraphs.get(i));
        }
        System.out.println();

        // Prints the shortest path from vertex 0 to vertex 3. This certainly
        // exists for our particular directed graph.
        System.out.println("Shortest path from 0 to 3:");
        List path =
            DijkstraShortestPath.findPathBetween(directedGraph, 0, 3);
        System.out.println(path + "\n");

    }
}

However, I get the error "unexpected token int" at the line:

DirectedGraph<int, DefaultEdge> directedGraph =

I changed the arguments of the method to int so why am I getting this error?

possible duplicate of [Why don't Java Generics support primitive types?](http://stackoverflow.com/questions/2721546/why-dont-java-generics-support-primitive-types) — Andy Brown, Jul 24 '15 at 17:30
Might be a duplicate but I had no idea that my problem could be formulated like this — Graham Slick, Jul 24 '15 at 17:32

score 4 · Accepted Answer · edited Jul 25 '15 at 19:10

4

You can't use the primitive types as generics, so change it to Integer. Autoboxing will work so you won't have to change everything else to Integer.

edited Jul 25 '15 at 19:10

Bobulous

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answered Jul 24 '15 at 17:28

Arhowk

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score 1 · Answer 2 · answered Jul 24 '15 at 17:28

In Java's generics, a primitive type such as int is not allowed as a type parameter. As a substitute, you can use Java's wrapper types for primitive types. Here you can use Integer instead of int.

DirectedGraph<Integer, DefaultEdge> directedGraph = // ,...

Java's boxing/unboxing features will handle the conversion from int to Integer and back implicitly.

Error when changing method argument from String to int

2 Answers2