The previous object has no methods for changing the values of the object, aside from changing the fields directly with an assignment statement.
A way to enforce the non-changeability of those fields is to declare them private:
class pair{private int x;private int y;... rest as before ....}
Now there is no way to change the values in the object once it is created.
Such objects are called immutable.
Functional programming, in a sense, deals only with immutable objects.
If we add a setter capability, such as setX, setY, then the objects in the class would be mutable.
void setX(int x) // set the x value{this.x = x;}
int setY(int y) // set the y value{this.y = y;}
Note that these methods would change the value returned by min, as well as the values returned by getX and getY.
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