Java的Comparable接口的一个陷阱(2)

这个实现看起来没问题，假设现在这个类提供的信息不够使用，我们又创建了这个类的一个子类CompanyDetail类用以扩展他。例如我们想以一个表的形式显示公司的信息，我们就可以用这个类。

public class CompanyDetails extends Company {
 
    private final String marketingName;
    private final Double marketValue;
 
    public CompanyDetails(final String id, final String officialName, final String marketingName, final Double marketValue) {
        super(id, officialName);
        this.marketingName = marketingName;
        this.marketValue = marketValue;
    }
 
    public String getMarketingName() {
        return marketingName;
    }
 
    public Double getMarketValue() {
        return marketValue;
    }
 
    @Override
    public int hashCode() {
        HashCodeBuilder builder = new HashCodeBuilder(19, 31);
        builder.appendSuper(super.hashCode());
        builder.append(this.getMarketingName());
        return builder.toHashCode();
    }
 
    @Override
    public boolean equals(final Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof CompanyDetails)) {
            return false;
        }
        CompanyDetails other = (CompanyDetails) obj;
        EqualsBuilder builder = new EqualsBuilder();
        builder.appendSuper(super.equals(obj));
        builder.append(this.getMarketingName(), other.getMarketingName());
        builder.append(this.getMarketValue(), other.getMarketValue());
        return builder.isEquals();
    }
}