How will Hashmap key behave if hash code is overridden such that it returns only a constant number?

Question

I have a small question about Java Hashmap. If I override the hashCode method such that:

@Override
public int hashCode(){
  return          


        

Answer 1

Whether it appears as a linked list or not is debatable as it does not state in the documentation. However, it will certainly keep all items with unique keys (i.e. keys that return true to the equals method).

class Nine {

    final String value;

    public Nine(String value) {
        this.value = value;
    }

    @Override
    public int hashCode() {
        return 9;
    }

    @Override
    public boolean equals(Object it) {
        return it instanceof Nine && ((Nine) it).value.equals(value);
    }

    @Override
    public String toString() {
        return value;
    }
}

class AlwaysNine extends Nine {

    public AlwaysNine(String value) {
        super(value);
    }

    @Override
    public boolean equals(Object it) {
        return it instanceof Nine;
    }
}

public void test() {
    System.out.println("Hello");
    Map testMap = new HashMap();
    testMap.put(new Nine("Nine"), "Nine");
    testMap.put(new Nine("nine"), "nine");
    testMap.put(new AlwaysNine("nIne"), "nIne");
    System.out.println(testMap);
}

prints

{Nine=nIne, nine=nine}

which proves that only overriding equals will force keys to seem to be the same ... as expected because hashCode is only used to pick the bucket in which to place the object.