GuavaTermsExplained

Glossary

antisymmetric

An antisymmetric relation is any relation such that a.relation(b) && b.relation(a) always implies that a and b are equal.

associative

An associative operation is any binary operation for which a.operation(b).operation(c) always equals a.operation(b.operation(c)).

binary operation

A binary operator (such as +), or a method of the form static A operation(A first, A second), or a method in a class A of the form A operation(A second).

commutative

An operation is commutative if a.operation(b) always equals b.operation(a).

See symmetric for the analogous property of relations.

equal

In referring to primitives, p1 and p2 are called equal if and only if p1 == p2. In referring to objects, unless specified otherwise, a1 and a2 are called equal if and only if a1.equals(a2). When we intend identity equality we will clearly say, "the same instance as." (Range is an example of a class that specifies a different meaning for "equal".)

equivalence relation

An equivalence relation is any binary relation that is reflexive, symmetric and transitive. The contract of Object.equals specifies that it must define an equivalence relation.

idempotent

In an idempotent operation, a.operation().operation() always equals a.operation().

lazy

A lazy view does not query the backing object until it absolutely has to. For example, Iterators.filter(Iterator, Predicate) returns an Iterator that only advances the backing iterator when a new element is demanded.

partial ordering

A relation is said to be a partial ordering if it is reflexive, transitive, and antisymmetric. If it also has the property that a.relation(b) || b.relation(a) for all a and b, it is a total ordering.

primitive

A boolean, byte, short, char, int, float, long or double.

reflexive

In a reflexive relation, a.relation(a) is always true.

relation

A relational operator (such as <), or a method of the form static boolean relation(A first, A second), or a method in a class A of the form boolean relation(A second).

symmetric

In a symmetric relation, a1.relation(a2) always has the same boolean value as a2.relation(a1).

total ordering

A total ordering is any relation that is antisymmetric, transitive, and has the property that a.relation(b) or b.relation(a) holds. (It follows that relation is reflexive.)

For example, when we say that a Comparator must define a total ordering, we mean that the relation comparator.compare(a, b) <= 0 satisfies:

• comparator.compare(a, b) <= 0 && comparator.compare(b, a) <= 0 does imply that comparator.compare(a, b) == 0, and if the ordering is consistent with equals, a.equals(b).
• comparator.compare(a, b) <= 0 && comparator.compare(b, c) <= 0 implies that comparator.compare(a, c) <= 0.
• For all a, b, comparator.compare(a, b) <= 0 || comparator.compare(b, a) <= 0.

transitive

For a transitive relation, a1.relation(a2) && a2.relation(a3) always implies that a1.relation(a3).