新知--contains();

用contains()方法，需要重写 equals与 hashCode方法

eg: public class Authority

@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((url == null) ? 0 : url.hashCode());
return result;
}

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Authority other = (Authority) obj;
    if (url == null) {
        if (other.url != null)
            return false;
    } else if (!url.equals(other.url))
        return false;
    return true;
}