Using Java’s Arrays.sort() for any List of Objects

Sorting can be tricky, especially when your list is not of a primitive Java numeric type (Byte, Integer, Short, Long, Double, Float). Now, all situations will vary so this method might not be the best case. However, I’ve found it incredibly useful for simple coding challenges and university lab assignments.

To start, pick your list. For this example I’ll be using a list of Edges from a simple Graph data structure:

// Very simple Edge classpublic class Edge {    public Vertex src;    public Vertex dst;    public double cost;        // creates an edge between two vertices    Edge(Vertex s, Vertex d, double c) {        src = s;        dst = d;        cost = c;    }}

// List of edgesEdge[] edges = graph.getEdges();

Next, define the implementation of the java.util.Comparator interface:

class SortByCost implements Comparator<Edge> {    public int compare(Edge a, Edge b) {        if ( a.cost < b.cost ) return -1;        else if ( a.cost == b.cost ) return 0;        else return 1;    }}

In this example, we will be sorting the edges by their cost, or distance from the src (source) vertex to the dst (destination) vertex.

Finally use the standard java.util.Arrays.sort() method:

Arrays.sort(edges, new SortByCost())

And just like that, the list of Edges is now sorted in ascending (least to greatest) order.

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~ Happy Coding

— Ethan Arrowood