What situations do you need to use them both, and with what collections?

you have to override both if you need either of them
if you want a particular class to be check for equality on their properties, then it makes sense to override it
usually when the class is an entity it's better to leave the default implementation

ty!

The hashCode() and equals() methods are used to compare objects in Java.

The hashCode() method returns an integer value that represents the hash code of an object. This value is used by certain collections, such as HashSet and HashMap, to quickly identify if two objects are likely to be equal.

The equals() method is used to compare the actual contents of two objects to determine if they are equal.

In most cases, if you override the equals() method, you should also override the hashCode() method. This is because if two objects are equal according to the equals() method, they should also have the same hash code.

Therefore, you would typically use both methods when working with collections that rely on hash codes for efficiency, such as HashSet, HashMap, Hashtable, and IdentityHashMap.

Additionally, you might also use both methods when implementing your own classes that need to be compared for equality, especially if you plan on using them in collections that rely on hash codes.