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Why does Java HashMap containskey always return false?
Debugging the java source code I realized that the method containsKey checks two things on the searched key against every element in the key set: hashCode and equals; and it does it in that order. It means that if obj1.hashCode () != obj2.hashCode (), it returns false (without evaluating obj1.equals (obj2).
How is the hashCode stored in a hashmap?
If you look at the implementation of HashMap, you’ll see that each key-value pair is stored along with the key’s hash code. When the map wants to check the stored key against an incoming one, it uses both this hashCode and the key’s equals:
Can a mutable object be used as a map key?
Note: great care must be exercised if mutable objects are used as map keys. The behavior of a map is not specified if the value of an object is changed in a manner that affects equals comparisons while the object is a key in the map.
What does it mean when hashCode returns false in Java?
It means that if obj1.hashCode () != obj2.hashCode (), it returns false (without evaluating obj1.equals (obj2). But, if obj1.hashCode () == obj2.hashCode (), then it returns obj1.equals (obj2) You have to be sure that both methods -may be you have to override them- evaluate to true for your defined criteria.
How are equals and hashCode methods used in Java?
Java.lang.object has two very important methods defined: public boolean equals(Object obj) and public int hashCode(). equals() method. In java equals() method is used to compare equality of two Objects. The equality can be compared in two ways:
What does it mean when both objects have the same hashCode?
Both Objects are equal. Here, First we are comparing the hashCode on both Objects (i.e. g1 and g2) and if same hashcode is generated by both the Objects that does not mean that they are equal as hashcode can be same for different Objects also, if they have the same id (in this case).
Can a map be keyed from a company name?
The created map always has Id as the key, so you won’t be able to lookup company name in there. If you want a mapped keyed from company name, you’ll need to construct it yourself. Not the answer you’re looking for?