flink 中自定义类的 hashCode() 和 equals() 方法 [英] hashCode() and equals() method for custom classes in flink

问题描述

我怀疑 Flink 中的自定义类是否需要覆盖 hashCode() 和 equals() 方法，因为我已经阅读了 这个页面 hashCode() 绝不能在分布式系统中实现，Apache Flink 就是其中之一.

my doubt is about if custom classes in Flink with Java needs to override or not hashCode() and equals() methods because I have read in this page that hashCode() MUST never be implemented in distributed systems and Apache Flink is one of them.

示例:我有这个类:

public class EventCounter {
    public String Id;
    public long count;
    public Timestamp firstEvent;
    public Timestamp lastEvent;
    public Date date;

    public EventCounter() {
    }
}

我需要在 Flink 中为此类类实现 hashCode() 和 equals() 还是让 Flink 管理这些方法对性能更好是自己的吗?

Do I need to implement hashCode() and equals() for this kind of classes in Flink or it is better for performance if I let Flink manage those methods on it's own?

亲切的问候！

推荐答案

要在 Flink 中用作键的类型(即，作为从 KeySelector 返回的值)必须具有 hashCode 和 equals 的有效实现.特别是，hashCode 必须在 JVM 之间具有确定性(这就是数组和枚举在 Flink 中不能作为键的原因).

Types that you want to use as keys in Flink (i.e., as values you return from a KeySelector) must have valid implementations of hashCode and equals. In particular, hashCode must be deterministic across JVMs (which is why arrays and enums don't work as keys in Flink).

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