All Superinterfaces:

Preference

All Known Implementing Classes:

MutablePreferenceImpl
```
public interface MutablePreference
extends Preference
```
A mutable preference keeps two graphs: the one representing the information received directly from the voter, not necessarily transitive or reflexive, given by asMutableGraph(); and the one we deduce, which is at all times transitively closed and reflexive, given by Preference.asGraph().

To improve performance, avoid calling Preference.asGraph() before modifying the preference, as this obliges this class to maintain the transitive closure.

The transitive closure of the graph must be interpreted with caution while it is building, even when the graph is mutated only by adding edges (never by removing any). When the mutable graph has an edge from a to b but not from b to a, the transitive closure will seem to say that a is strictly preferred to b, which we can’t deduce: this is valid when the preferential information in input is complete (otherwise, perhaps b ≥ a in supplement to a ≥ b and they are tied).

This interface does not promote any specific notion of equality. The alternative would have been, either, to define a specific notion of equality for a mutable preference (having the same mutable graph), or re-use the natural notion of equality for a general preference, that is, having the same transitive graph. The second one would have been surprising, as two mutable preferences with different mutable graphs could have ended up being equal. And, in any case, it is not generally considered a good idea to rely on equality of a mutable object.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`addAlternative(Alternative alternative)`	Adds an alternative to the Preference.
`void`	`addEquivalence(Alternative a1, Alternative a2)`	Adds an edge from an alternative a1 to an alternative a2 and from a2 to a1.
`MutableGraph<Alternative>`	`asMutableGraph()`	This graph is not necessarily transitive and not necessarily reflexive.
`void`	`setAsLeastAsGood(Alternative a1, Alternative a2)`	Adds an edge from an alternative a1 to an alternative a2, so that a1 is as least as good as a2 (a1 >= a2).

Methods inherited from interface io.github.oliviercailloux.j_voting.preferences.Preference
asGraph, getAlternatives, getVoter

- Method Detail
  - asMutableGraph
```
MutableGraph<Alternative> asMutableGraph()
```
    This graph is not necessarily transitive and not necessarily reflexive.
  - addAlternative
```
void addAlternative(Alternative alternative)
```
    Adds an alternative to the Preference. This alternative is not preferred to any other of the preference, it is being added isolated.
    
    Parameters:
    
    alternative - to add to the preference.
  - addEquivalence
```
void addEquivalence(Alternative a1,
                    Alternative a2)
```
    Adds an edge from an alternative a1 to an alternative a2 and from a2 to a1. If one of them is not in the graph, they are added. a1 and a2 are ex-aequo.
    
    Parameters:
    
    a1 - first alternative
    
    a2 - second alternative
  - setAsLeastAsGood
```
void setAsLeastAsGood(Alternative a1,
                      Alternative a2)
```
    Adds an edge from an alternative a1 to an alternative a2, so that a1 is as least as good as a2 (a1 >= a2). If one of them is not in the graph, they are added.
    
    Parameters:
    
    a1 - preferred alternative to a2
    
    a2 - "lower" alternative

Interface MutablePreference

Method Summary

Methods inherited from interface io.github.oliviercailloux.j_voting.preferences.Preference

Method Detail

asMutableGraph

addAlternative

addEquivalence

setAsLeastAsGood