覆盖equals（）&子类中的hashCode（）...考虑超级字段 [英] Overriding equals() & hashCode() in sub classes ... considering super fields

问题描述

是否有关于如何覆盖等于（）&的特定规则考虑超级字段，子类中的 hashCode（）知道有很多参数：超级字段是私有/公共的，有/无getter ...

Is there a specific rule on how Overriding equals() & hashCode() in sub classes considering super fields ?? knowing that there is many parameters : super fields are private/public , with/without getter ...

例如，Netbeans生成了equals（）& hashCode（）不会考虑超级字段......和

For instance, Netbeans generated equals() & hashCode() will not consider the super fields ... and

    new HomoSapiens("M", "80", "1.80", "Cammeron", "VeryHot").equals(
    new HomoSapiens("F", "50", "1.50", "Cammeron", "VeryHot"))

将返回true :(

will return true :(

public class Hominidae {

    public String  gender;
    public String  weight;
    public String  height;

    public Hominidae(String gender, String weight, String height) {
        this.gender = gender;
        this.weight = weight;
        this.height = height;
    }
    ... 
}

public class HomoSapiens extends Hominidae {
    public String name;
    public String faceBookNickname;

    public HomoSapiens(String gender, String weight, String height, 
                       String name, String facebookId) {
        super(gender, weight, height);
        this.name = name;
        this.faceBookNickname = facebookId;
    }
    ...  
}

如果你想看看Netbeans生成的equals（）& hashCode（）：

If you want to see the Netbeans generated equals() & hashCode() :

public class Hominidae {

    ...

    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final Hominidae other = (Hominidae) obj;
        if ((this.gender == null) ? (other.gender != null) : !this.gender.equals(other.gender)) {
            return false;
        }
        if ((this.weight == null) ? (other.weight != null) : !this.weight.equals(other.weight)) {
            return false;
        }
        if ((this.height == null) ? (other.height != null) : !this.height.equals(other.height)) {
            return false;
        }
        return true;
    }

    @Override
    public int hashCode() {
        int hash = 5;
        hash = 37 * hash + (this.gender != null ? this.gender.hashCode() : 0);
        hash = 37 * hash + (this.weight != null ? this.weight.hashCode() : 0);
        hash = 37 * hash + (this.height != null ? this.height.hashCode() : 0);
        return hash;
    }

}


public class HomoSapiens extends Hominidae {

    ...

    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final HomoSapiens other = (HomoSapiens) obj;
        if ((this.name == null) ? (other.name != null) : !this.name.equals(other.name)) {
            return false;
        }
        if ((this.faceBookNickname == null) ? (other.faceBookNickname != null) : !this.faceBookNickname.equals(other.faceBookNickname)) {
            return false;
        }
        return true;
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 89 * hash + (this.name != null ? this.name.hashCode() : 0);
        hash = 89 * hash + (this.faceBookNickname != null ? this.faceBookNickname.hashCode() : 0);
        return hash;
    }
}

推荐答案

< b>孩子不应该检查父母的私人成员

但显然是，所有重要的字段都应该考虑在内平等和散列。

But obviously, all significant fields should be taken into account for equality and hashing.

幸运的是，你可以很容易地满足这两个规则。

Fortunately, you you can easily satisfy both rules.

假设你没有卡住使用NetBeans生成的equals和hashcode，您可以修改Hominidae的equals方法以使用instanceof比较而不是类相等，然后直接使用它。这样的事情：

Assuming you're not stuck using the NetBeans-generated equals and hashcode, you can modify Hominidae's equals method to use instanceof comparison rather than class equality, and then use it straightforwardly. Something like this:

    @Override  
    public boolean equals(Object obj) {  
        if (obj == null) { return false; }  
        if (getClass() != obj.getClass()) { return false; }  
        if (! super.equals(obj)) return false;
        else {
           // compare subclass fields
        }

当然，哈希码很简单：

    @Override     
    public int hashCode() {     
        int hash = super.hashCode();
        hash = 89 * hash + (this.name != null ? this.name.hashCode() : 0);     
        hash = 89 * hash + (this.faceBookNickname != null ? this.faceBookNickname.hashCode() : 0);     
        return hash;     
    }     

但是，严重的是：NetBeans没有通过调用将超类字段考虑在内超类方法？

Seriously, though: what's up with NetBeans not taking superclass fields into account by calling the superclass methods?

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