Java Object. equals

Can someone tell me why this returns true?

Please tell me under which topic I can find more information about this behavior

Set<String> s1 = new HashSet<String>(as("a"));
   Set<String> s2 = new HashSet<String>(as("a"));

   Object o1 = (Object)s1;
   Object o2 = (Object)s2;

   System.out.println(o1.equals(o2));

Solution

Methods in Java are virtual by default In particular, object Equals is virtual (because it is not declared final) From HashSet overrides object Starting with equals1, you'll see a HashSet implementation of equal when calling a virtual method on an object of runtime type HashSet (remember that dynamic dispatch depends on the runtime type of the receiving object, not the compile time type)

1: We know that HashSet will overwrite object Equals, because Documentation means that HashSet is derived from abstractset, while abstractset The equals document says:

It explicitly defines equal values, and the default object Equals is identity equality