Example1.java

public class Foo {

    private final String firstName;
    
    public Foo(String firstName) {
        this.firstName = firstName;
    }
    
    public String getFirstName() {
        return firstName;
    }
    
    @Override 
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        } 
        else if (!(obj instanceof Foo)) {
            return false;
        } 
        else {
            Foo foo = (Foo) obj;
            return Objects.equals(foo.firstName, firstName);
        }
    }
    public int hashCode() { /* ... */ }
}

public class Bar extends Foo {

    public Bar(String firstName) {
        super(firstName);
    }
}

Foo foo = new Foo("John");
Bar bar = new Bar("John");
System.out.println(foo.equals(bar)); // true
System.out.println(bar.equals(foo)); // true