Question

我有ViewPartner类

public class ViewPartner {
    private int id;
    private boolean enabled;

    public ViewPartner(int id, boolean enabled) {
        this.id = id;
        this.enabled = enabled;
    }

    @Override
    public boolean equals(Object o){
        if(o instanceof ViewPartner){
            return id == ((ViewPartner) o).id;
        } else {
            return false;
        }
    }
}

和包含以下方法的ViewPartnerContainer类：

public class SelectedViewPartnerContainer {
    private Map<Integer, List<ViewPartner>> cahcedPagePartnersMap;
    private Set<ViewPartner> rawPartners;

    //GET, SET ,Contructor and other methods

    public Collection<ViewPartner> getRawPartners(Set<ViewPartner> partners){
        for(ViewPartner vp : partners){
            if(rawPartners.contains(vp)){
                partners.add(vp);
            }
        }
        return partners;
    }
}

现在我有以下代码：

SelectedViewPartnerContainer c = new SelectedViewPartnerContainer();
Set<ViewPartner> partners = new HashSet<ViewPartner>();
List<ViewPartner> rawLst = new ArrayList<ViewPartner>();
for(int i = 40; i < 50; i++){
    rawLst.add(new ViewPartner(i, false));
}
for(int i = 37; i < 42; i++){
    partners.add(new ViewPartner(i, true));
}
//adding rawLst to the c's rawPartners property
ViewPartner p2 = new ViewPartner(40, false);
Collection<ViewPartner> co = c.getRawPartners(partners);
List<ViewPartner> co2 = new ArrayList(c.getRawPartners(partners));
co.contains(p2); //false
co2.contains(p2); //true

为什么contains方法之间存在差异？

Answer 1

HashSet<ViewPartner>无法正常运行，因为ViewPartner未实现hashCode()。读取Object.equals API：通常需要在重写此方法时覆盖hashCode方法，以便维护hashCode方法的常规协定，该方法声明相等的对象必须具有相等的哈希代码。

Collection和List包含方法

1 个答案: