I Found a SECRET HashMap Nobody Talks About скачать в хорошем качестве

I Found a SECRET HashMap Nobody Talks About

You put a value in a HashMap. You know it’s there. But when you try to get it back… it’s null. This isn’t a Java bug. It’s an equals() / hashCode() contract violation. In this video, we do a full HashMap autopsy using a simple ProductId key class: We store "Gaming Laptop" under new ProductId("A-100") We try to retrieve it using a new ProductId("A-100") It fails (returns null) because the hash codes don’t match Then we fix it by correctly overriding equals() and hashCode() What you’ll learn ✅ Why HashMap uses hash codes (“buckets”) first ✅ The rule: If two objects are equal, their hashCode MUST be the same ✅ The common mistake: overriding one but not the other ✅ The clean fix for custom key classes If you use custom objects as keys in HashMap/HashSet, this is a must-know. Code files used: ProductId.java (the patient) HashMapAutopsy.java (the autopsy) #java #hashmap #equals #hashcode #programming #javabugs #collections