org.lockss.tdb.Predicates Maven / Gradle / Ivy
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*/
package org.lockss.tdb;
/**
*
* Useful {@link Predicate} utilities.
*
*
* @author Thib Guicherd-Callin
* @since 1.67
*/
public class Predicates {
/**
*
* Prevent instantionation.
*
*
* @since 1.67
*/
private Predicates() {
// Prevent instantiation
}
/**
*
* A predicate that is always true.
*
*
* @author Thib Guicherd-Callin
* @param The argument type over which the predicate applies.
* @since 1.67
*/
public static class TruePredicate implements Predicate {
@Override
public boolean test(A a) {
return true;
}
}
/**
*
* A predicate that is always false.
*
*
* @author Thib Guicherd-Callin
* @param The argument type over which the predicate applies.
* @since 1.67
*/
public static class FalsePredicate implements Predicate {
@Override
public boolean test(A a) {
return false;
}
}
/**
*
* An abstract predicate that has another predicate as a member.
*
*
* @author Thib Guicherd-Callin
* @param The argument type over which the predicate applies.
* @since 1.67
*/
public static abstract class UnaryPredicate implements Predicate {
/**
*
* A predicate.
*
*
* @since 1.67
*/
protected Predicate predicate1;
/**
*
* Makes a new unary predicate with the given predicate.
*
*
* @param predicate1 A predicate.
*/
public UnaryPredicate(Predicate predicate1) {
this.predicate1 = predicate1;
}
}
/**
*
* A predicate that is the opposite of another predicate.
*
*
* @author Thib Guicherd-Callin
* @param The argument type over which the predicate applies.
* @since 1.67
*/
public static class NotPredicate extends UnaryPredicate {
/**
*
* Makes a new predicate that is the opposite of the given predicate.
*
*
* @param predicate1 A predicate to negate.
* @since 1.67
*/
public NotPredicate(Predicate predicate1) {
super(predicate1);
}
@Override
public boolean test(A a) {
return !predicate1.test(a);
}
}
/**
*
* An abstract predicate that has two other predicates as members.
*
*
* @author Thib Guicherd-Callin
* @param The argument type over which the predicate applies.
* @since 1.67
*/
public static abstract class BinaryPredicate extends UnaryPredicate {
/**
*
* Another predicate.
*
*
* @since 1.67
*/
protected Predicate predicate2;
/**
*
* Makes a new binary predicate with the two given predicates.
*
*
* @param predicate1 A predicate.
* @param predicate2 Another predicate.
* @since 1.67
*/
public BinaryPredicate(Predicate predicate1,
Predicate predicate2) {
super(predicate1);
this.predicate2 = predicate2;
}
}
/**
*
* A predicate that is true if and only if both of its constituent predicates
* are true.
*
* This is implemented in usual short-circuit manner: if the first
* predicate evaluates to false, the second predicate is not evaluated.
*
* @author Thib Guicherd-Callin
* @param The argument type over which the predicate applies.
* @since 1.67
*/
public static class AndPredicate extends BinaryPredicate {
/**
*
* Makes a new predicate that is true if and only if both given predicates
* are true.
*
*
* @param predicate1 A predicate.
* @param predicate2 Another predicate.
* @since 1.67
*/
public AndPredicate(Predicate predicate1,
Predicate predicate2) {
super(predicate1, predicate2);
}
@Override
public boolean test(A a) {
return predicate1.test(a) && predicate2.test(a);
}
}
/**
*
* A predicate that is true if and only if either of its constituent
* predicates is true.
*
*
* This is implemented in usual short-circuit manner: if the first
* predicate evaluates to true, the second predicate is not evaluated.
*
*
* @author Thib Guicherd-Callin
* @param
* The argument type over which the predicate applies.
* @since 1.67
*/
public static class OrPredicate extends BinaryPredicate {
/**
*
* Makes a new predicate that is true if and only if either given predicates
* is true.
*
*
* @param predicate1 A predicate.
* @param predicate2 Another predicate.
* @since 1.67
*/
public OrPredicate(Predicate predicate1,
Predicate predicate2) {
super(predicate1, predicate2);
}
@Override
public boolean test(A a) {
return predicate1.test(a) || predicate2.test(a);
}
}
}