JPA 实体和抽象实体上的 equals 方法

发布于 2024-12-10 19:25:57 字数 417 浏览 0 评论 0原文

我有一个抽象实体类，由 3 个略有不同的实体实现。在我的 3 个子类中，我已经重写了 equals 和 has 方法，但问题是，我也应该在抽象实体中执行此操作吗？如果我不这样做，我将无法比较仅由抽象实体定义的实体，除非我对它们进行强制转换。如果我进行平等，我是否会冒险与不同的子实体进行比较并发现它们是相似的？

例子：

abstract class Log{}
SystemLog extends Log{}
UserLog extends Log{}

    public void test(Log log){
        Log myInner = new SystemLog();
        if(log.equals(myInner)){
            //do random stuff
        }
    }

原文

I have a abstract entity class that 3 slightly different entities implements. In my 3 sub classes I have overriden the equals and has methods but the question is, should I also do this in the abstract entity? If I dont I will not be able to compare entities that are only defined by abstract entity unless i cast them. If i do a equals will I risk to compare to different sub entities and get that they are alike?

Example:

abstract class Log{}
SystemLog extends Log{}
UserLog extends Log{}

    public void test(Log log){
        Log myInner = new SystemLog();
        if(log.equals(myInner)){
            //do random stuff
        }
    }

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东北女汉子 2024-12-17 19:25:57

我看不出铸造有问题。 equals 的参数类型是 Object，因此您必须进行强制转换才能访问属性。

如果在每个子类中都定义了 equals 方法，那么什么时候会出现调用抽象超类中的 equals 的情况呢？

如果我做平等，我会冒与不同子实体进行比较的风险吗？
发现他们很相似

您都面临着将不同子实体相互比较的风险。想象一下，使用超类作为类型填充的对象是两个不同子类的两个实例。它与您是否覆盖超类中的 equals 没有太大关系。

在您的示例中，如果我们已经在实际子类中实现了，则可能不会调用抽象类 Log 中可能实现的 equals 方法：

假设：

UserLog extends Log{
    public boolean equals(Object o) {
        //I do override equals method so I am one who is called.
        //and here you go and check type with something like
    if (this == o) return true;
    if (!(o instanceof UserLog)) return false;//accepts subclasses of UserLog
     ....
    }
  ...
}

//And then somewhere else
  Log ul = new UserLog();
  test(ul);

I cannot see problem with casting. Type of argument to equals is Object, so you have to cast anyway to have access to attributes.

If you define equals method in each subclasses, when comes the situation where equals in abstract superclass is called?

If i do a equals will I risk to compare to different sub entities and
get that they are alike

You are in the risk of comparing different subentities to each others anyway. Just imagine Set with superclass as type populated with objects that are two instances of two different subclasses. It has not too much to do with do you override equals in superclass or not.

In your example equals method possibly implemented in abstract class Log will not be called, if we have implementation already in actual subclass:

Assuming:

UserLog extends Log{
    public boolean equals(Object o) {
        //I do override equals method so I am one who is called.
        //and here you go and check type with something like
    if (this == o) return true;
    if (!(o instanceof UserLog)) return false;//accepts subclasses of UserLog
     ....
    }
  ...
}

//And then somewhere else
  Log ul = new UserLog();
  test(ul);

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