predicateutils.java

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/*
 *  Copyright 2002-2004 The Apache Software Foundation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.commons.collections;

import java.util.Collection;

import org.apache.commons.collections.functors.AllPredicate;
import org.apache.commons.collections.functors.AndPredicate;
import org.apache.commons.collections.functors.AnyPredicate;
import org.apache.commons.collections.functors.EqualPredicate;
import org.apache.commons.collections.functors.ExceptionPredicate;
import org.apache.commons.collections.functors.FalsePredicate;
import org.apache.commons.collections.functors.IdentityPredicate;
import org.apache.commons.collections.functors.InstanceofPredicate;
import org.apache.commons.collections.functors.InvokerTransformer;
import org.apache.commons.collections.functors.NonePredicate;
import org.apache.commons.collections.functors.NotNullPredicate;
import org.apache.commons.collections.functors.NotPredicate;
import org.apache.commons.collections.functors.NullIsExceptionPredicate;
import org.apache.commons.collections.functors.NullIsFalsePredicate;
import org.apache.commons.collections.functors.NullIsTruePredicate;
import org.apache.commons.collections.functors.NullPredicate;
import org.apache.commons.collections.functors.OnePredicate;
import org.apache.commons.collections.functors.OrPredicate;
import org.apache.commons.collections.functors.TransformedPredicate;
import org.apache.commons.collections.functors.TransformerPredicate;
import org.apache.commons.collections.functors.TruePredicate;
import org.apache.commons.collections.functors.UniquePredicate;

/**
 * <code>PredicateUtils</code> provides reference implementations and utilities
 * for the Predicate functor interface. The supplied predicates are:
 * <ul>
 * <li>Invoker - returns the result of a method call on the input object
 * <li>InstanceOf - true if the object is an instanceof a class
 * <li>Equal - true if the object equals() a specified object
 * <li>Identity - true if the object == a specified object
 * <li>Null - true if the object is null
 * <li>NotNull - true if the object is not null
 * <li>Unique - true if the object has not already been evaluated
 * <li>And/All - true if all of the predicates are true
 * <li>Or/Any - true if any of the predicates is true
 * <li>Either/One - true if only one of the predicate is true
 * <li>Neither/None - true if none of the predicates are true
 * <li>Not - true if the predicate is false, and vice versa
 * <li>Transformer - wraps a Transformer as a Predicate
 * <li>True - always return true
 * <li>False - always return false
 * <li>Exception - always throws an exception
 * <li>NullIsException/NullIsFalse/NullIsTrue - check for null input
 * <li>Transformed - transforms the input before calling the predicate
 * </ul>
 * All the supplied predicates are Serializable.
 *
 * @since Commons Collections 3.0
 * @version $Revision: 1.19 $ $Date: 2004/05/26 21:50:52 $
 * 
 * @author Stephen Colebourne
 * @author Ola Berg
 */
public class PredicateUtils {

    /**
     * This class is not normally instantiated.
     */
    public PredicateUtils() {
        super();
    }

    // Simple predicates
    //-----------------------------------------------------------------------------

    /** 
     * Gets a Predicate that always throws an exception.
     * This could be useful during testing as a placeholder.
     *
     * @see org.apache.commons.collections.functors.ExceptionPredicate
     * 
     * @return the predicate
     */
    public static Predicate exceptionPredicate() {
        return ExceptionPredicate.INSTANCE;
    }

    /**
     * Gets a Predicate that always returns true.
     * 
     * @see org.apache.commons.collections.functors.TruePredicate
     * 
     * @return the predicate
     */
    public static Predicate truePredicate() {
        return TruePredicate.INSTANCE;
    }

    /**
     * Gets a Predicate that always returns false.
     * 
     * @see org.apache.commons.collections.functors.FalsePredicate
     * 
     * @return the predicate
     */
    public static Predicate falsePredicate() {
        return FalsePredicate.INSTANCE;
    }

    /**
     * Gets a Predicate that checks if the input object passed in is null.
     * 
     * @see org.apache.commons.collections.functors.NullPredicate
     * 
     * @return the predicate
     */
    public static Predicate nullPredicate() {
        return NullPredicate.INSTANCE;
    }

    /**
     * Gets a Predicate that checks if the input object passed in is not null.
     * 
     * @see org.apache.commons.collections.functors.NotNullPredicate
     * 
     * @return the predicate
     */
    public static Predicate notNullPredicate() {
        return NotNullPredicate.INSTANCE;
    }

    /**
     * Creates a Predicate that checks if the input object is equal to the
     * specified object using equals().
     * 
     * @see org.apache.commons.collections.functors.EqualPredicate
     * 
     * @param value  the value to compare against
     * @return the predicate
     */
    public static Predicate equalPredicate(Object value) {
        return EqualPredicate.getInstance(value);
    }

    /**
     * Creates a Predicate that checks if the input object is equal to the
     * specified object by identity.
     * 
     * @see org.apache.commons.collections.functors.IdentityPredicate
     * 
     * @param value  the value to compare against
     * @return the predicate
     */
    public static Predicate identityPredicate(Object value) {
        return IdentityPredicate.getInstance(value);
    }
    
    /**
     * Creates a Predicate that checks if the object passed in is of
     * a particular type, using instanceof. A <code>null</code> input
     * object will return <code>false</code>.
     * 
     * @see org.apache.commons.collections.functors.InstanceofPredicate
     * 
     * @param type  the type to check for, may not be null
     * @return the predicate
     * @throws IllegalArgumentException if the class is null
     */
    public static Predicate instanceofPredicate(Class type) {
        return InstanceofPredicate.getInstance(type);
    }

    /**
     * Creates a Predicate that returns true the first time an object is
     * encountered, and false if the same object is received 
     * again. The comparison is by equals(). A <code>null</code> input object
     * is accepted and will return true the first time, and false subsequently
     * as well.
     * 
     * @see org.apache.commons.collections.functors.UniquePredicate
     * 
     * @return the predicate
     */
    public static Predicate uniquePredicate() {
        // must return new instance each time
        return UniquePredicate.getInstance();
    }

    /**
     * Creates a Predicate that invokes a method on the input object.
     * The method must return either a boolean or a non-null Boolean,
     * and have no parameters. If the input object is null, a 
     * PredicateException is thrown.
     * <p>
     * For example, <code>PredicateUtils.invokerPredicate("isEmpty");</code>
     * will call the <code>isEmpty</code> method on the input object to 
     * determine the predicate result.
     * 
     * @see org.apache.commons.collections.functors.InvokerTransformer
     * @see org.apache.commons.collections.functors.TransformerPredicate
     * 
     * @param methodName  the method name to call on the input object, may not be null
     * @return the predicate
     * @throws IllegalArgumentException if the methodName is null.
     */
    public static Predicate invokerPredicate(String methodName){
        // reuse transformer as it has caching - this is lazy really, should have inner class here
        return asPredicate(InvokerTransformer.getInstance(methodName));
    }

    /**
     * Creates a Predicate that invokes a method on the input object.
     * The method must return either a boolean or a non-null Boolean,
     * and have no parameters. If the input object is null, a 
     * PredicateException is thrown.
     * <p>
     * For example, <code>PredicateUtils.invokerPredicate("isEmpty");</code>
     * will call the <code>isEmpty</code> method on the input object to 
     * determine the predicate result.
     * 
     * @see org.apache.commons.collections.functors.InvokerTransformer
     * @see org.apache.commons.collections.functors.TransformerPredicate
     * 
     * @param methodName  the method name to call on the input object, may not be null
     * @param paramTypes  the parameter types
     * @param args  the arguments
     * @return the predicate
     * @throws IllegalArgumentException if the method name is null
     * @throws IllegalArgumentException if the paramTypes and args don't match
     */
    public static Predicate invokerPredicate(String methodName, Class[] paramTypes, Object[] args){
        // reuse transformer as it has caching - this is lazy really, should have inner class here
        return asPredicate(InvokerTransformer.getInstance(methodName, paramTypes, args));
    }

    // Boolean combinations
    //-----------------------------------------------------------------------------

    /**
     * Create a new Predicate that returns true only if both of the specified
     * predicates are true.
     * 
     * @see org.apache.commons.collections.functors.AndPredicate
     * 
     * @param predicate1  the first predicate, may not be null
     * @param predicate2  the second predicate, may not be null
     * @return the <code>and</code> predicate
     * @throws IllegalArgumentException if either predicate is null
     */
    public static Predicate andPredicate(Predicate predicate1, Predicate predicate2) {
        return AndPredicate.getInstance(predicate1, predicate2);
    }

    /**
     * Create a new Predicate that returns true only if all of the specified
     * predicates are true.
     * 
     * @see org.apache.commons.collections.functors.AllPredicate