Object-Oriented Java - Java 8 Recipes - page 182

These object references contain the same values.
How It Works
The comparison operator (==) can be used to determine the equality of two objects.
This equality does not pertain to the object values, but rather to the object references.
Often an application is more concerned with the values of objects; in such cases, the
equals() method is the preferred choice because it compares the values contained
within the objects rather than the object references.
The comparison operator takes a look at the object reference and determines wheth-
er it points to the same object as the object reference that it is being compared against.
If the two objects are equal, a Boolean true result will be returned; otherwise, a
Boolean false result will be returned. In solution 1, the first comparison between
the team1 object reference and the team2 object reference returns a false value be-
cause those two objects are separate in memory, even though they contain the same
values. The second comparison in solution 1 between the team3 object reference and
the team4 object reference returns a true value because both of those references refer
to the team1 object.
The equals() method can be used to test whether two objects contain the same
values. In order to use the equals() method for comparison, the object that is being
compared should override the Object class equals() and hashCode() methods.
The equals() method should implement a comparison against the values contained
within the object that would yield a true comparison result. The following code is an
example of an overridden equals() method that has been placed into the Team ob-
ject:
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj instanceof Team) {
Team other = (Team) obj;
return other.getName().equals(this.getName())
&& other.getCity().equals(this.getCity())
&& other.getPlayers().equals(this.getPlayers());