java - 用 OR 条件覆盖哈希码

Question

我正在写一个 pojo ，我正在覆盖 hashcode 和 equals ， 但是我使对象相等的条件是具有 OR 条件。在这种情况下如何编写哈希码？？？

比如我有一个pojo，有aaa,bbb,ccc三个字段 和处理相等的条件是，aaa 必须相等并且 bbb 或 ccc 应该相等。我在等于覆盖部分写了这个但是在这种情况下在哈希码中写什么？？？

public class POJO {

private String aaa;
private String bbb;
private String ccc;

///How to use or condition here ???????
@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((aaa == null) ? 0 : aaa.hashCode());
    result = prime * result + ((bbb == null) ? 0 : bbb.hashCode());
    return result;
}
//my condition is aaa and (bbb or ccc) should be equal
@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    POJO other = (POJO) obj;
    if (aaa == null) {
        if (other.aaa != null)
            return false;
    } else if (!aaa.equals(other.aaa))
        return false;
    if (bbb == null || ccc == null) {
        if (other.bbb != null || other.ccc != null)
            return false;
   //This is the main condition
    } else if (!bbb.equals(other.bbb) || !ccc.equals(other.ccc))
        return false;
    return true;
}
public String getAaa() {
    return aaa;
}
public void setAaa(String aaa) {
    this.aaa = aaa;
}
public String getBbb() {
    return bbb;
}
public void setBbb(String bbb) {
    this.bbb = bbb;
}
public String getCcc() {
    return ccc;
}
public void setCcc(String ccc) {
    this.ccc = ccc;
}




}

Answer 1

你的equals逻辑不一致，所以你不能定义一致的hashCode。

假设您有 3 个具有以下值的对象:

   aaa    bbb  ccc

   "a1"  "b1"  "c1"
   "a1"  "b1"  "c2"
   "a1"  "b2"  "c2"

按照你的逻辑，第一个对象等于第二个(aaa 和 bbb 属性都相等)，第二个等于第三个(aaa 和 ccc 属性都相等)，但是第一个是不等于第三个(因为 bbb 和 ccc 属性不相等)。 equals 必须是可传递的。

来自Javadoc :

The equals method implements an equivalence relation on non-null object references:

• It is reflexive: for any non-null reference value x, x.equals(x) should return true.
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
• It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
• It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
• For any non-null reference value x, x.equals(null) should return false.