Can we use any class as Map key in Java if yes how, if no then why not?

Answer 1

Yes we can use any class as a map key in java,suppose we have a class name named MyMap so here is some description of MaMap class
See this example:

 //MyKey name argument passed is used for equals() and hashCode()
    MyKey key = new MyKey('Shivam Pandey'); //assume hashCode=1234
    myHashMap.put(key, 'Value');

    // Below code will change the key hashCode() and equals()
    // but it's location is not changed.
    key.setName('ShashiKant'); //assume new hashCode=7890

    //below will return null, because HashMap will try to look for key
    //in the same index as it was stored but since key is mutated, 
    //there will be no match and it will return null.
    myHashMap.get(new MyKey('Shivam Pandey'));

credits: https://www.javacodegeeks.com/2013/02/40-java-collections-interview-questions-and-answers.html#map-key

Answer 2

Yes, we can use any class as a key in the map as long as the class implements equals and hashcode methods ..