Flyweight Pattern

[_uj]

Which data in these objects iin this example are similar that he share?

In that example whole Time objects are shared.

Time objects are not created using new directly. Instead a factory method is called. The factory method keeps track of all Time objects it creates. If a specific Time object already has been created before, the factory method returns a reference to this existing object rather than creating a new one. So if you do,

Time t1 = TimeFactory.create(12, 50);
Time t2 = TimeFactory.create(12, 50);

the factory method (called create) will make sure both t1 and t2 refers to the same object. So t1==t2 will be true. This is the Flyweight sharing.

Note that String literals are treated according to the same principle. If you do,

String s1 = "hello";
String s2 = "hello";

Then both s1 and s2 will refer to the same String object. So s1==s2 will be true.

Also note that this kind of Flyweight sharing requires objects to be immutable (after creation the object state cannot be changed).