Java

Question

我有TreeSet<Rate>的列表。我需要List中所有TreeSet的交集。我检查reatainAll它正在制作两套，如果我错了，请纠正我。 List的最大大小为8。

我怎样才能得到所有这些集合的交集？

 public class Rate implements Comparable<Rate> {

private double value = 0.00;
private int restuarentID = 0;

//setters and getters

@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + restuarentID;
    long temp;
    temp = Double.doubleToLongBits(value);
    result = prime * result + (int) (temp ^ (temp >>> 32));
    return result;
}

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Rate other = (Rate) obj;
    if (restuarentID != other.restuarentID)
        return false;
    if (Double.doubleToLongBits(value) != Double.doubleToLongBits(other.value))
        return false;
    return true;
}

@Override
public int compareTo(Rate o) {
    int ret = 0;
    if (this.getValue() > o.getValue())
        ret = 1;
    if (this.getValue() < o.getValue())
        ret = -1;
    if (this.getValue() == o.getValue())
        ret = 0;
    return ret;
}

}

Answer 1

您可以这样做：

public static TreeSet<Rate> intersect(List<TreeSet<Rate>> setList) {
    if (setList.isEmpty()) {
        throw new IllegalArgumentException("Need at least one TreeSet in list");
    }
    Iterator<TreeSet<Rate>> it = setList.iterator();
    TreeSet<Rate> result = new TreeSet<>(it.next());
    while (it.hasNext()) {
        result.retainAll(it.next());
    }
    return result;
}