Edge.java

// 边
public class Edge<Weight extends Number & Comparable> implements Comparable<Edge<Weight>>{

    private int a, b;    // 边的两个端点
    private Weight weight;  // 边的权值

    public Edge(int a, int b, Weight weight)
    {
        this.a = a;
        this.b = b;
        this.weight = weight;
    }

    public Edge(Edge<Weight> e)
    {
        this.a = e.a;
        this.b = e.b;
        this.weight = e.weight;
    }

    public int v(){ return a;} // 返回第一个顶点
    public int w(){ return b;} // 返回第二个顶点
    public Weight wt(){ return weight;}    // 返回权值

    // 给定一个顶点, 返回另一个顶点
    public int other(int x){
        assert x == a || x == b;
        return x == a ? b : a;
    }

    // 输出边的信息
    public String toString(){
        return "" + a + "-" + b + ": " + weight;
    }

    // 边之间的比较
    public int compareTo(Edge<Weight> that)
    {
        if( weight.compareTo(that.wt()) < 0 )
            return -1;
        else if ( weight.compareTo(that.wt()) > 0 )
            return +1;
        else
            return  0;
    }
}