/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.lang;

import org.apache.commons.lang.math.NumberUtils;

/**
 * <p>Operations on boolean primitives and Boolean objects.</p>
 *
 * <p>This class tries to handle <code>null</code> input gracefully.
 * An exception will not be thrown for a <code>null</code> input.
 * Each method documents its behaviour in more detail.</p>
 * 
 * @author Stephen Colebourne
 * @author Matthew Hawthorne
 * @author Gary Gregory
 * @since 2.0
 * @version $Id$
 */
public class BooleanUtils {

    /**
     * <p><code>BooleanUtils</code> instances should NOT be constructed in standard programming.
     * Instead, the class should be used as <code>BooleanUtils.toBooleanObject(true);</code>.</p>
     *
     * <p>This constructor is public to permit tools that require a JavaBean instance
     * to operate.</p>
     */
    public BooleanUtils() {
      super();
    }

    // Boolean utilities
    //--------------------------------------------------------------------------
    /**
     * <p>Negates the specified boolean.</p>
     * 
     * <p>If <code>null</code> is passed in, <code>null</code> will be returned.</p>
     *
     * <pre>
     *   BooleanUtils.negate(Boolean.TRUE)  = Boolean.FALSE;
     *   BooleanUtils.negate(Boolean.FALSE) = Boolean.TRUE;
     *   BooleanUtils.negate(null)          = null;
     * </pre>
     * 
     * @param bool  the Boolean to negate, may be null
     * @return the negated Boolean, or <code>null</code> if <code>null</code> input
     */
    public static Boolean negate(Boolean bool) {
        if (bool == null) {
            return null;
        }
        return (bool.booleanValue() ? Boolean.FALSE : Boolean.TRUE);
    }
    
    // boolean Boolean methods
    //-----------------------------------------------------------------------
    /**
     * <p>Is a Boolean value <code>true</code>, handling <code>null</code>.</p>
     *
     * <pre>
     *   BooleanUtils.isTrue(Boolean.TRUE)  = true
     *   BooleanUtils.isTrue(Boolean.FALSE) = false
     *   BooleanUtils.isTrue(null)          = false
     * </pre>
     *
     * @param bool  the boolean to convert
     * @return <code>true</code> only if the input is non-null and true
     * @since 2.1
     */
    public static boolean isTrue(Boolean bool) {
        if (bool == null) {
            return false;
        }
        return bool.booleanValue() ? true : false;
    }

    /**
     * <p>Is a Boolean value <code>false</code>, handling <code>null</code>.</p>
     *
     * <pre>
     *   BooleanUtils.isFalse(Boolean.TRUE)  = false
     *   BooleanUtils.isFalse(Boolean.FALSE) = true
     *   BooleanUtils.isFalse(null)          = false
     * </pre>
     *
     * @param bool  the boolean to convert
     * @return <code>true</code> only if the input is non-null and false
     * @since 2.1
     */
    public static boolean isFalse(Boolean bool) {
        if (bool == null) {
            return false;
        }
        return bool.booleanValue() ? false : true;
    }

    /**
     * <p>Boolean factory that avoids creating new Boolean objecs all the time.</p>
     * 
     * <p>This method was added to JDK1.4 but is available here for earlier JDKs.</p>
     *
     * <pre>
     *   BooleanUtils.toBooleanObject(false) = Boolean.FALSE
     *   BooleanUtils.toBooleanObject(true)  = Boolean.TRUE
     * </pre>
     *
     * @param bool  the boolean to convert
     * @return Boolean.TRUE or Boolean.FALSE as appropriate
     */
    public static Boolean toBooleanObject(boolean bool) {
        return bool ? Boolean.TRUE : Boolean.FALSE;
    }
    
    /**
     * <p>Converts a Boolean to a boolean handling <code>null</code>
     * by returning <code>false</code>.</p>
     *
     * <pre>
     *   BooleanUtils.toBoolean(Boolean.TRUE)  = true
     *   BooleanUtils.toBoolean(Boolean.FALSE) = false
     *   BooleanUtils.toBoolean(null)          = false
     * </pre>
     *
     * @param bool  the boolean to convert
     * @return <code>true</code> or <code>false</code>, 
     *  <code>null</code> returns <code>false</code>
     */
    public static boolean toBoolean(Boolean bool) {
        if (bool == null) {
            return false;
        }
        return bool.booleanValue() ? true : false;
    }
    
    /**
     * <p>Converts a Boolean to a boolean handling <code>null</code>.</p>
     * 
     * <pre>
     *   BooleanUtils.toBooleanDefaultIfNull(Boolean.TRUE, false) = true
     *   BooleanUtils.toBooleanDefaultIfNull(Boolean.FALSE, true) = false
     *   BooleanUtils.toBooleanDefaultIfNull(null, true)          = true
     * </pre>
     *
     * @param bool  the boolean to convert
     * @param valueIfNull  the boolean value to return if <code>null</code>
     * @return <code>true</code> or <code>false</code>
     */
    public static boolean toBooleanDefaultIfNull(Boolean bool, boolean valueIfNull) {
        if (bool == null) {
            return valueIfNull;
        }
        return bool.booleanValue() ? true : false;
    }
    
    // Integer to Boolean methods
    //-----------------------------------------------------------------------
    /**
     * <p>Converts an int to a boolean using the convention that <code>zero</code>
     * is <code>false</code>.</p>
     * 
     * <pre>
     *   BooleanUtils.toBoolean(0) = false
     *   BooleanUtils.toBoolean(1) = true
     *   BooleanUtils.toBoolean(2) = true
     * </pre>
     *
     * @param value  the int to convert
     * @return <code>true</code> if non-zero, <code>false</code>
     *  if zero
     */
    public static boolean toBoolean(int value) {
        return value == 0 ? false : true;
    }
    
    /**
     * <p>Converts an int to a Boolean using the convention that <code>zero</code>
     * is <code>false</code>.</p>
     * 
     * <pre>
     *   BooleanUtils.toBoolean(0) = Boolean.FALSE
     *   BooleanUtils.toBoolean(1) = Boolean.TRUE
     *   BooleanUtils.toBoolean(2) = Boolean.TRUE
     * </pre>
     *
     * @param value  the int to convert
     * @return Boolean.TRUE if non-zero, Boolean.FALSE if zero,
     *  <code>null</code> if <code>null</code>
     */
    public static Boolean toBooleanObject(int value) {
        return value == 0 ? Boolean.FALSE : Boolean.TRUE;
    }
    
    /**
     * <p>Converts an Integer to a Boolean using the convention that <code>zero</code>
     * is <code>false</code>.</p>
     * 
     * <p><code>null</code> will be converted to <code>null</code>.</p>
     *
     * <pre>
     *   BooleanUtils.toBoolean(new Integer(0))    = Boolean.FALSE
     *   BooleanUtils.toBoolean(new Integer(1))    = Boolean.TRUE
     *   BooleanUtils.toBoolean(new Integer(null)) = null
     * </pre>
     *
     * @param value  the Integer to convert
     * @return Boolean.TRUE if non-zero, Boolean.FALSE if zero,
     *  <code>null</code> if <code>null</code> input
     */
    public static Boolean toBooleanObject(Integer value) {
        if (value == null) {
            return null;
        }
        return value.intValue() == 0 ? Boolean.FALSE : Boolean.TRUE;
    }
    
    /**
     * <p>Converts an int to a boolean specifying the conversion values.</p>
     * 
     * <pre>
     *   BooleanUtils.toBoolean(0, 1, 0) = false
     *   BooleanUtils.toBoolean(1, 1, 0) = true
     *   BooleanUtils.toBoolean(2, 1, 2) = false
     *   BooleanUtils.toBoolean(2, 2, 0) = true
     * </pre>
     *
     * @param value  the Integer to convert
     * @param trueValue  the value to match for <code>true</code>
     * @param falseValue  the value to match for <code>false</code>
     * @return <code>true</code> or <code>false</code>
     * @throws IllegalArgumentException if no match
     */
    public static boolean toBoolean(int value, int trueValue, int falseValue) {
        if (value == trueValue) {
            return true;
        } else if (value == falseValue) {
            return false;
        }
        // no match
        throw new IllegalArgumentException("The Integer did not match either specified value");
    }
    
    /**
     * <p>Converts an Integer to a boolean specifying the conversion values.</p>
     * 
     * <pre>
     *   BooleanUtils.toBoolean(new Integer(0), new Integer(1), new Integer(0)) = false
     *   BooleanUtils.toBoolean(new Integer(1), new Integer(1), new Integer(0)) = true
     *   BooleanUtils.toBoolean(new Integer(2), new Integer(1), new Integer(2)) = false
     *   BooleanUtils.toBoolean(new Integer(2), new Integer(2), new Integer(0)) = true
     *   BooleanUtils.toBoolean(null, null, new Integer(0))                     = true
     * </pre>
     *
     * @param value  the Integer to convert
     * @param trueValue  the value to match for <code>true</code>,
     *  may be <code>null</code>
     * @param falseValue  the value to match for <code>false</code>,
     *  may be <code>null</code>
     * @return <code>true</code> or <code>false</code>
     * @throws IllegalArgumentException if no match
     */
    public static boolean toBoolean(Integer value, Integer trueValue, Integer falseValue) {
        if (value == null) {
            if (trueValue == null) {
                return true;
            } else if (falseValue == null) {
                return false;
            }
        } else if (value.equals(trueValue)) {
            return true;
        } else if (value.equals(falseValue)) {
            return false;
        }
        // no match
        throw new IllegalArgumentException("The Integer did not match either specified value");
    }
    
    /**
     * <p>Converts an int to a Boolean specifying the conversion values.</p>
     * 
     * <pre>
     *   BooleanUtils.toBooleanObject(0, 0, 2, 3) = Boolean.TRUE
     *   BooleanUtils.toBooleanObject(2, 1, 2, 3) = Boolean.FALSE
     *   BooleanUtils.toBooleanObject(3, 1, 2, 3) = null
     * </pre>
     *
     * @param value  the Integer to convert
     * @param trueValue  the value to match for <code>true</code>
     * @param falseValue  the value to match for <code>false</code>
     * @param nullValue  the value to to match for <code>null</code>
     * @return Boolean.TRUE, Boolean.FALSE, or <code>null</code>
     * @throws IllegalArgumentException if no match
     */
    public static Boolean toBooleanObject(int value, int trueValue, int falseValue, int nullValue) {
        if (value == trueValue) {
            return Boolean.TRUE;
        } else if (value == falseValue) {
            return Boolean.FALSE;
        } else if (value == nullValue) {
            return null;
        }
        // no match
        throw new IllegalArgumentException("The Integer did not match any specified value");
    }
    
    /**
     * <p>Converts an Integer to a Boolean specifying the conversion values.</p>
     * 
     * <pre>
     *   BooleanUtils.toBooleanObject(new Integer(0), new Integer(0), new Integer(2), new Integer(3)) = Boolean.TRUE
     *   BooleanUtils.toBooleanObject(new Integer(2), new Integer(1), new Integer(2), new Integer(3)) = Boolean.FALSE
     *   BooleanUtils.toBooleanObject(new Integer(3), new Integer(1), new Integer(2), new Integer(3)) = null
     * </pre>
     *
     * @param value  the Integer to convert
     * @param trueValue  the value to match for <code>true</code>,
     *  may be <code>null</code>
     * @param falseValue  the value to match for <code>false</code>,
     *  may be <code>null</code>
     * @param nullValue  the value to to match for <code>null</code>,
     *  may be <code>null</code>
     * @return Boolean.TRUE, Boolean.FALSE, or <code>null</code>
     * @throws IllegalArgumentException if no match
     */
    public static Boolean toBooleanObject(Integer value, Integer trueValue, Integer falseValue, Integer nullValue) {
        if (value == null) {
            if (trueValue == null) {
                return Boolean.TRUE;
            } else if (falseValue == null) {
                return Boolean.FALSE;
            } else if (nullValue == null) {
                return null;
            }
        } else if (value.equals(trueValue)) {
            return Boolean.TRUE;
        } else if (value.equals(falseValue)) {
            return Boolean.FALSE;
        } else if (value.equals(nullValue)) {
            return null;
        }
        // no match
        throw new IllegalArgumentException("The Integer did not match any specified value");
    }
    
    // Boolean to Integer methods
    //-----------------------------------------------------------------------
    /**
     * <p>Converts a boolean to an int using the convention that
     * <code>zero</code> is <code>false</code>.</p>
     *
     * <pre>
     *   BooleanUtils.toInteger(true)  = 1
     *   BooleanUtils.toInteger(false) = 0
     * </pre>
     *
     * @param bool  the boolean to convert
     * @return one if <code>true</code>, zero if <code>false</code>
     */
    public static int toInteger(boolean bool) {
        return bool ? 1 : 0;
    }
    
    /**
     * <p>Converts a boolean to an Integer using the convention that
     * <code>zero</code> is <code>false</code>.</p>
     * 
     * <pre>
     *   BooleanUtils.toIntegerObject(true)  = new Integer(1)
     *   BooleanUtils.toIntegerObject(false) = new Integer(0)
     * </pre>
     *
     * @param bool  the boolean to convert
     * @return one if <code>true</code>, zero if <code>false</code>
     */
    public static Integer toIntegerObject(boolean bool) {
        return bool ? NumberUtils.INTEGER_ONE : NumberUtils.INTEGER_ZERO;
    }
    
    /**
     * <p>Converts a Boolean to a Integer using the convention that
     * <code>zero</code> is <code>false</code>.</p>
     *
     * <p><code>null</code> will be converted to <code>null</code>.</p>
     *
     * <pre>
     *   BooleanUtils.toIntegerObject(Boolean.TRUE)  = new Integer(1)
     *   BooleanUtils.toIntegerObject(Boolean.FALSE) = new Integer(0)
     * </pre>
     *
     * @param bool  the Boolean to convert
     * @return one if Boolean.TRUE, zero if Boolean.FALSE, <code>null</code> if <code>null</code>
     */
    public static Integer toIntegerObject(Boolean bool) {
        if (bool == null) {
            return null;
        }
        return bool.booleanValue() ? NumberUtils.INTEGER_ONE : NumberUtils.INTEGER_ZERO;
    }
    
    /**
     * <p>Converts a boolean to an int specifying the conversion values.</p>
     * 
     * <pre>
     *   BooleanUtils.toInteger(true, 1, 0)  = 1
     *   BooleanUtils.toInteger(false, 1, 0) = 0
     * </pre>
     *
     * @param bool  the to convert
     * @param trueValue  the value to return if <code>true</code>
     * @param falseValue  the value to return if <code>false</code>
     * @return the appropriate value
     */
    public static int toInteger(boolean bool, int trueValue, int falseValue) {
        return bool ? trueValue : falseValue;
    }
    
    /**
     * <p>Converts a Boolean to an int specifying the conversion values.</p>
     * 
     * <pre>
     *   BooleanUtils.toInteger(Boolean.TRUE, 1, 0, 2)  = 1
     *   BooleanUtils.toInteger(Boolean.FALSE, 1, 0, 2) = 0
     *   BooleanUtils.toInteger(null, 1, 0, 2)          = 2
     * </pre>
     *
     * @param bool  the Boolean to convert
     * @param trueValue  the value to return if <code>true</code>
     * @param falseValue  the value to return if <code>false</code>
     * @param nullValue  the value to return if <code>null</code>
     * @return the appropriate value
     */
    public static int toInteger(Boolean bool, int trueValue, int falseValue, int nullValue) {
        if (bool == null) {
            return nullValue;
        }
        return bool.booleanValue() ? trueValue : falseValue;
    }
    
    /**
     * <p>Converts a boolean to an Integer specifying the conversion values.</p>
     * 
     * <pre>
     *   BooleanUtils.toIntegerObject(true, new Integer(1), new Integer(0))  = new Integer(1)
     *   BooleanUtils.toIntegerObject(false, new Integer(1), new Integer(0)) = new Integer(0)
     * </pre>
     *
     * @param bool  the to convert
     * @param trueValue  the value to return if <code>true</code>,
     *  may be <code>null</code>
     * @param falseValue  the value to return if <code>false</code>,
     *  may be <code>null</code>
     * @return the appropriate value
     */
    public static Integer toIntegerObject(boolean bool, Integer trueValue, Integer falseValue) {
        return bool ? trueValue : falseValue;
    }
    
    /**
     * <p>Converts a Boolean to an Integer specifying the conversion values.</p>
     * 
     * <pre>
     *   BooleanUtils.toIntegerObject(Boolean.TRUE, new Integer(1), new Integer(0), new Integer(2))  = new Integer(1)
     *   BooleanUtils.toIntegerObject(Boolean.FALSE, new Integer(1), new Integer(0), new Integer(2)) = new Integer(0)
     *   BooleanUtils.toIntegerObject(null, new Integer(1), new Integer(0), new Integer(2))          = new Integer(2)
     * </pre>
     *
     * @param bool  the Boolean to convert
     * @param trueValue  the value to return if <code>true</code>,
     *  may be <code>null</code>
     * @param falseValue  the value to return if <code>false</code>,
     *  may be <code>null</code>
     * @param nullValue  the value to return if <code>null</code>,
     *  may be <code>null</code>
     * @return the appropriate value
     */
    public static Integer toIntegerObject(Boolean bool, Integer trueValue, Integer falseValue, Integer nullValue) {
        if (bool == null) {
            return nullValue;
        }
        return bool.booleanValue() ? trueValue : falseValue;
    }
    
    // String to Boolean methods
    //-----------------------------------------------------------------------
    /**
     * <p>Converts a String to a Boolean.</p>
     * 
     * <p><code>'true'</code>, <code>'on'</code> or <code>'yes'</code>
     * (case insensitive) will return <code>true</code>.
     * <code>'false'</code>, <code>'off'</code> or <code>'no'</code>
     * (case insensitive) will return <code>false</code>.
     * Otherwise, <code>null</code> is returned.</p>
     *
     * <pre>
     *   BooleanUtils.toBooleanObject(null)    = null
     *   BooleanUtils.toBooleanObject("true")  = Boolean.TRUE
     *   BooleanUtils.toBooleanObject("false") = Boolean.FALSE
     *   BooleanUtils.toBooleanObject("on")    = Boolean.TRUE
     *   BooleanUtils.toBooleanObject("ON")    = Boolean.TRUE
     *   BooleanUtils.toBooleanObject("off")   = Boolean.FALSE
     *   BooleanUtils.toBooleanObject("oFf")   = Boolean.FALSE
     *   BooleanUtils.toBooleanObject("blue")  = null
     * </pre>
     *
     * @param str  the String to check
     * @return the Boolean value of the string,
     *  <code>null</code> if no match or <code>null</code> input
     */
    public static Boolean toBooleanObject(String str) {
        if ("true".equalsIgnoreCase(str)) {
            return Boolean.TRUE;
        } else if ("false".equalsIgnoreCase(str)) {
            return Boolean.FALSE;
        } else if ("on".equalsIgnoreCase(str)) {
            return Boolean.TRUE;
        } else if ("off".equalsIgnoreCase(str)) {
            return Boolean.FALSE;
        } else if ("yes".equalsIgnoreCase(str)) {
            return Boolean.TRUE;
        } else if ("no".equalsIgnoreCase(str)) {
            return Boolean.FALSE;
        }
        // no match
        return null;
    }

    /**
     * <p>Converts a String to a Boolean throwing an exception if no match.</p>
     *
     * <pre>
     *   BooleanUtils.toBooleanObject("true", "true", "false", "null")  = Boolean.TRUE
     *   BooleanUtils.toBooleanObject("false", "true", "false", "null") = Boolean.FALSE
     *   BooleanUtils.toBooleanObject("null", "true", "false", "null")  = null
     * </pre>
     *
     * @param str  the String to check
     * @param trueString  the String to match for <code>true</code>
     *  (case sensitive), may be <code>null</code>
     * @param falseString  the String to match for <code>false</code>
     *  (case sensitive), may be <code>null</code>
     * @param nullString  the String to match for <code>null</code>
     *  (case sensitive), may be <code>null</code>
     * @return the Boolean value of the string,
     *  <code>null</code> if no match or <code>null</code> input
     */
    public static Boolean toBooleanObject(String str, String trueString, String falseString, String nullString) {
        if (str == null) {
            if (trueString == null) {
                return Boolean.TRUE;
            } else if (falseString == null) {
                return Boolean.FALSE;
            } else if (nullString == null) {
                return null;
            }
        } else if (str.equals(trueString)) {
            return Boolean.TRUE;
        } else if (str.equals(falseString)) {
            return Boolean.FALSE;
        } else if (str.equals(nullString)) {
            return null;
        }
        // no match
        throw new IllegalArgumentException("The String did not match any specified value");
    }

    // String to boolean methods
    //-----------------------------------------------------------------------
    /**
     * <p>Converts a String to a boolean (optimised for performance).</p>
     * 
     * <p><code>'true'</code>, <code>'on'</code> or <code>'yes'</code>
     * (case insensitive) will return <code>true</code>. Otherwise,
     * <code>false</code> is returned.</p>
     * 
     * <p>This method performs 4 times faster (JDK1.4) than
     * <code>Boolean.valueOf(String)</code>. However, this method accepts
     * 'on' and 'yes' as true values.
     *
     * <pre>
     *   BooleanUtils.toBoolean(null)    = false
     *   BooleanUtils.toBoolean("true")  = true
     *   BooleanUtils.toBoolean("TRUE")  = true
     *   BooleanUtils.toBoolean("tRUe")  = true
     *   BooleanUtils.toBoolean("on")    = true
     *   BooleanUtils.toBoolean("yes")   = true
     *   BooleanUtils.toBoolean("false") = false
     *   BooleanUtils.toBoolean("x gti") = false
     * </pre>
     *
     * @param str  the String to check
     * @return the boolean value of the string, <code>false</code> if no match
     */
    public static boolean toBoolean(String str) {
        // Previously used equalsIgnoreCase, which was fast for interned 'true'.
        // Non interned 'true' matched 15 times slower.
        // 
        // Optimisation provides same performance as before for interned 'true'.
        // Similar performance for null, 'false', and other strings not length 2/3/4.
        // 'true'/'TRUE' match 4 times slower, 'tRUE'/'True' 7 times slower.
        if (str == "true") {
            return true;
        }
        if (str == null) {
            return false;
        }
        switch (str.length()) {
            case 2: {
                char ch0 = str.charAt(0);
                char ch1 = str.charAt(1);
                return 
                    (ch0 == 'o' || ch0 == 'O') &&
                    (ch1 == 'n' || ch1 == 'N');
            }
            case 3: {
                char ch = str.charAt(0);
                if (ch == 'y') {
                    return 
                        (str.charAt(1) == 'e' || str.charAt(1) == 'E') &&
                        (str.charAt(2) == 's' || str.charAt(2) == 'S');
                }
                if (ch == 'Y') {
                    return 
                        (str.charAt(1) == 'E' || str.charAt(1) == 'e') &&
                        (str.charAt(2) == 'S' || str.charAt(2) == 's');
                }
            }
            case 4: {
                char ch = str.charAt(0);
                if (ch == 't') {
                    return 
                        (str.charAt(1) == 'r' || str.charAt(1) == 'R') &&
                        (str.charAt(2) == 'u' || str.charAt(2) == 'U') &&
                        (str.charAt(3) == 'e' || str.charAt(3) == 'E');
                }
                if (ch == 'T') {
                    return 
                        (str.charAt(1) == 'R' || str.charAt(1) == 'r') &&
                        (str.charAt(2) == 'U' || str.charAt(2) == 'u') &&
                        (str.charAt(3) == 'E' || str.charAt(3) == 'e');
                }
            }
        }
        return false;
    }
    
//    public static void main(String[] args) {
//        long start = System.currentTimeMillis();
//        boolean flag = true;
//        int count = 0;
//        for (int i = 0; i < 100000000; i++) {
//            flag = toBoolean("YES");
//        }
//        long end = System.currentTimeMillis();
//        System.out.println((end - start) + " " + flag + " " + count);
//    }
    
    /**
     * <p>Converts a String to a Boolean throwing an exception if no match found.</p>
     * 
     * <p>null is returned if there is no match.</p>
     *
     * <pre>
     *   BooleanUtils.toBoolean("true", "true", "false")  = true
     *   BooleanUtils.toBoolean("false", "true", "false") = false
     * </pre>
     *
     * @param str  the String to check
     * @param trueString  the String to match for <code>true</code>
     *  (case sensitive), may be <code>null</code>
     * @param falseString  the String to match for <code>false</code>
     *  (case sensitive), may be <code>null</code>
     * @return the boolean value of the string
     * @throws IllegalArgumentException if the String doesn't match
     */
    public static boolean toBoolean(String str, String trueString, String falseString) {
        if (str == null) {
            if (trueString == null) {
                return true;
            } else if (falseString == null) {
                return false;
            }
        } else if (str.equals(trueString)) {
            return true;
        } else if (str.equals(falseString)) {
            return false;
        }
        // no match
        throw new IllegalArgumentException("The String did not match either specified value");
    }

    // Boolean to String methods
    //-----------------------------------------------------------------------
    /**
     * <p>Converts a Boolean to a String returning <code>'true'</code>,
     * <code>'false'</code>, or <code>null</code>.</p>
     * 
     * <pre>
     *   BooleanUtils.toStringTrueFalse(Boolean.TRUE)  = "true"
     *   BooleanUtils.toStringTrueFalse(Boolean.FALSE) = "false"
     *   BooleanUtils.toStringTrueFalse(null)          = null;
     * </pre>
     *
     * @param bool  the Boolean to check
     * @return <code>'true'</code>, <code>'false'</code>,
     *  or <code>null</code>
     */
    public static String toStringTrueFalse(Boolean bool) {
        return toString(bool, "true", "false", null);
    }
    
    /**
     * <p>Converts a Boolean to a String returning <code>'on'</code>,
     * <code>'off'</code>, or <code>null</code>.</p>
     * 
     * <pre>
     *   BooleanUtils.toStringOnOff(Boolean.TRUE)  = "on"
     *   BooleanUtils.toStringOnOff(Boolean.FALSE) = "off"
     *   BooleanUtils.toStringOnOff(null)          = null;
     * </pre>
     *
     * @param bool  the Boolean to check
     * @return <code>'on'</code>, <code>'off'</code>,
     *  or <code>null</code>
     */
    public static String toStringOnOff(Boolean bool) {
        return toString(bool, "on", "off", null);
    }
    
    /**
     * <p>Converts a Boolean to a String returning <code>'yes'</code>,
     * <code>'no'</code>, or <code>null</code>.</p>
     * 
     * <pre>
     *   BooleanUtils.toStringYesNo(Boolean.TRUE)  = "yes"
     *   BooleanUtils.toStringYesNo(Boolean.FALSE) = "no"
     *   BooleanUtils.toStringYesNo(null)          = null;
     * </pre>
     *
     * @param bool  the Boolean to check
     * @return <code>'yes'</code>, <code>'no'</code>,
     *  or <code>null</code>
     */
    public static String toStringYesNo(Boolean bool) {
        return toString(bool, "yes", "no", null);
    }
    
    /**
     * <p>Converts a Boolean to a String returning one of the input Strings.</p>
     * 
     * <pre>
     *   BooleanUtils.toString(Boolean.TRUE, "true", "false", null)   = "true"
     *   BooleanUtils.toString(Boolean.FALSE, "true", "false", null)  = "false"
     *   BooleanUtils.toString(null, "true", "false", null)           = null;
     * </pre>
     *
     * @param bool  the Boolean to check
     * @param trueString  the String to return if <code>true</code>,
     *  may be <code>null</code>
     * @param falseString  the String to return if <code>false</code>,
     *  may be <code>null</code>
     * @param nullString  the String to return if <code>null</code>,
     *  may be <code>null</code>
     * @return one of the three input Strings
     */
    public static String toString(Boolean bool, String trueString, String falseString, String nullString) {
        if (bool == null) {
            return nullString;
        }
        return bool.booleanValue() ? trueString : falseString;
    }
    
    // boolean to String methods
    //-----------------------------------------------------------------------
    /**
     * <p>Converts a boolean to a String returning <code>'true'</code>
     * or <code>'false'</code>.</p>
     * 
     * <pre>
     *   BooleanUtils.toStringTrueFalse(true)   = "true"
     *   BooleanUtils.toStringTrueFalse(false)  = "false"
     * </pre>
     *
     * @param bool  the Boolean to check
     * @return <code>'true'</code>, <code>'false'</code>,
     *  or <code>null</code>
     */
    public static String toStringTrueFalse(boolean bool) {
        return toString(bool, "true", "false");
    }
    
    /**
     * <p>Converts a boolean to a String returning <code>'on'</code>
     * or <code>'off'</code>.</p>
     * 
     * <pre>
     *   BooleanUtils.toStringOnOff(true)   = "on"
     *   BooleanUtils.toStringOnOff(false)  = "off"
     * </pre>
     *
     * @param bool  the Boolean to check
     * @return <code>'on'</code>, <code>'off'</code>,
     *  or <code>null</code>
     */
    public static String toStringOnOff(boolean bool) {
        return toString(bool, "on", "off");
    }
    
    /**
     * <p>Converts a boolean to a String returning <code>'yes'</code>
     * or <code>'no'</code>.</p>
     * 
     * <pre>
     *   BooleanUtils.toStringYesNo(true)   = "yes"
     *   BooleanUtils.toStringYesNo(false)  = "no"
     * </pre>
     *
     * @param bool  the Boolean to check
     * @return <code>'yes'</code>, <code>'no'</code>,
     *  or <code>null</code>
     */
    public static String toStringYesNo(boolean bool) {
        return toString(bool, "yes", "no");
    }
    
    /**
     * <p>Converts a boolean to a String returning one of the input Strings.</p>
     * 
     * <pre>
     *   BooleanUtils.toString(true, "true", "false")   = "true"
     *   BooleanUtils.toString(false, "true", "false")  = "false"
     * </pre>
     *
     * @param bool  the Boolean to check
     * @param trueString  the String to return if <code>true</code>,
     *  may be <code>null</code>
     * @param falseString  the String to return if <code>false</code>,
     *  may be <code>null</code>
     * @return one of the two input Strings
     */
    public static String toString(boolean bool, String trueString, String falseString) {
        return bool ? trueString : falseString;
    }
    
    // xor methods
    // ----------------------------------------------------------------------
    /**
     * <p>Performs an xor on a set of booleans.</p>
     *
     * <pre>
     *   BooleanUtils.xor(new boolean[] { true, true })   = false
     *   BooleanUtils.xor(new boolean[] { false, false }) = false
     *   BooleanUtils.xor(new boolean[] { true, false })  = true
     * </pre>
     *
     * @param array  an array of <code>boolean<code>s
     * @return <code>true</code> if the xor is successful.
     * @throws IllegalArgumentException if <code>array</code> is <code>null</code>
     * @throws IllegalArgumentException if <code>array</code> is empty.
     */
    public static boolean xor(boolean[] array) {
        // Validates input
        if (array == null) {
            throw new IllegalArgumentException("The Array must not be null");
        } else if (array.length == 0) {
            throw new IllegalArgumentException("Array is empty");
        }

        // Loops through array, comparing each item
        int trueCount = 0;
        for (int i = 0; i < array.length; i++) {
            // If item is true, and trueCount is < 1, increments count
            // Else, xor fails
            if (array[i]) {
                if (trueCount < 1) {
                    trueCount++;
                } else {
                    return false;
                }
            }
        }

        // Returns true if there was exactly 1 true item
        return trueCount == 1;
    }

    /**
     * <p>Performs an xor on an array of Booleans.</p>
     * 
     * <pre>
     *   BooleanUtils.xor(new Boolean[] { Boolean.TRUE, Boolean.TRUE })   = Boolean.FALSE
     *   BooleanUtils.xor(new Boolean[] { Boolean.FALSE, Boolean.FALSE }) = Boolean.FALSE
     *   BooleanUtils.xor(new Boolean[] { Boolean.TRUE, Boolean.FALSE })  = Boolean.TRUE
     * </pre>
     *
     * @param array  an array of <code>Boolean<code>s
     * @return <code>true</code> if the xor is successful.
     * @throws IllegalArgumentException if <code>array</code> is <code>null</code>
     * @throws IllegalArgumentException if <code>array</code> is empty.
     * @throws IllegalArgumentException if <code>array</code> contains a <code>null</code>
     */
    public static Boolean xor(Boolean[] array) {
        if (array == null) {
            throw new IllegalArgumentException("The Array must not be null");
        } else if (array.length == 0) {
            throw new IllegalArgumentException("Array is empty");
        }
        boolean[] primitive = null;
        try {
            primitive = ArrayUtils.toPrimitive(array);
        } catch (NullPointerException ex) {
            throw new IllegalArgumentException("The array must not contain any null elements");
        }
        return xor(primitive) ? Boolean.TRUE : Boolean.FALSE;
    }

}