https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2008 The Guava Authors
 *
 * 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 com.google.common.primitives;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkElementIndex;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndexes;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import java.io.Serializable;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.RandomAccess;
import org.checkerframework.checker.nullness.qual.Nullable;


Static utility methods pertaining to boolean primitives, that are not already found in either Boolean or Arrays. 
See the Guava User Guide article on primitive utilities.

Author:Kevin Bourrillion
Since:1.0
/**
 * Static utility methods pertaining to {@code boolean} primitives, that are not already found in
 * either {@link Boolean} or {@link Arrays}.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
 *
 * @author Kevin Bourrillion
 * @since 1.0
 */
@GwtCompatible
public final class Booleans {
  private Booleans() {}

  
Comparators for Boolean values. 
/** Comparators for {@code Boolean} values. */
  private enum BooleanComparator implements Comparator<Boolean> {
    TRUE_FIRST(1, "Booleans.trueFirst()"),
    FALSE_FIRST(-1, "Booleans.falseFirst()");

    private final int trueValue;
    private final String toString;

    BooleanComparator(int trueValue, String toString) {
      this.trueValue = trueValue;
      this.toString = toString;
    }

    @Override
    public int compare(Boolean a, Boolean b) {
      int aVal = a ? trueValue : 0;
      int bVal = b ? trueValue : 0;
      return bVal - aVal;
    }

    @Override
    public String toString() {
      return toString;
    }
  }

  
Returns a Comparator<Boolean> that sorts true before false. 
This is particularly useful in Java 8+ in combination with Comparators.comparing, e.g. Comparators.comparing(Foo::hasBar, trueFirst()). 
Since:21.0
/**
   * Returns a {@code Comparator<Boolean>} that sorts {@code true} before {@code false}.
   *
   * <p>This is particularly useful in Java 8+ in combination with {@code Comparators.comparing},
   * e.g. {@code Comparators.comparing(Foo::hasBar, trueFirst())}.
   *
   * @since 21.0
   */
  @Beta
  public static Comparator<Boolean> trueFirst() {
    return BooleanComparator.TRUE_FIRST;
  }

  
Returns a Comparator<Boolean> that sorts false before true. 
This is particularly useful in Java 8+ in combination with Comparators.comparing, e.g. Comparators.comparing(Foo::hasBar, falseFirst()). 
Since:21.0
/**
   * Returns a {@code Comparator<Boolean>} that sorts {@code false} before {@code true}.
   *
   * <p>This is particularly useful in Java 8+ in combination with {@code Comparators.comparing},
   * e.g. {@code Comparators.comparing(Foo::hasBar, falseFirst())}.
   *
   * @since 21.0
   */
  @Beta
  public static Comparator<Boolean> falseFirst() {
    return BooleanComparator.FALSE_FIRST;
  }

  
Returns a hash code for value; equal to the result of invoking ((Boolean)
value).hashCode(). 
Java 8 users: use Boolean.hashCode(boolean) instead. 
Params:
  • value – a primitive boolean value
Returns:a hash code for the value
/**
   * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Boolean)
   * value).hashCode()}.
   *
   * <p><b>Java 8 users:</b> use {@link Boolean#hashCode(boolean)} instead.
   *
   * @param value a primitive {@code boolean} value
   * @return a hash code for the value
   */
  public static int hashCode(boolean value) {
    return value ? 1231 : 1237;
  }

  
Compares the two specified boolean values in the standard way (false is considered less than true). The sign of the value returned is the same as that of ((Boolean) a).compareTo(b). 
Note for Java 7 and later: this method should be treated as deprecated; use the equivalent Boolean.compare method instead. 
Params:
  • a – the first boolean to compare
  • b – the second boolean to compare
Returns:a positive number if only a is true, a negative number if only 
    b is true, or zero if a == b
/**
   * Compares the two specified {@code boolean} values in the standard way ({@code false} is
   * considered less than {@code true}). The sign of the value returned is the same as that of
   * {@code ((Boolean) a).compareTo(b)}.
   *
   * <p><b>Note for Java 7 and later:</b> this method should be treated as deprecated; use the
   * equivalent {@link Boolean#compare} method instead.
   *
   * @param a the first {@code boolean} to compare
   * @param b the second {@code boolean} to compare
   * @return a positive number if only {@code a} is {@code true}, a negative number if only {@code
   *     b} is true, or zero if {@code a == b}
   */
  public static int compare(boolean a, boolean b) {
    return (a == b) ? 0 : (a ? 1 : -1);
  }

  
Returns true if target is present as an element anywhere in array. 
Note: consider representing the array as a BitSet instead, replacing Booleans.contains(array, true) with !bitSet.isEmpty() and 
Booleans.contains(array, false) with bitSet.nextClearBit(0) == sizeOfBitSet. 
Params:
  • array – an array of boolean values, possibly empty
  • target – a primitive boolean value
Returns:true if array[i] == target for some value of i
/**
   * Returns {@code true} if {@code target} is present as an element anywhere in {@code array}.
   *
   * <p><b>Note:</b> consider representing the array as a {@link java.util.BitSet} instead,
   * replacing {@code Booleans.contains(array, true)} with {@code !bitSet.isEmpty()} and {@code
   * Booleans.contains(array, false)} with {@code bitSet.nextClearBit(0) == sizeOfBitSet}.
   *
   * @param array an array of {@code boolean} values, possibly empty
   * @param target a primitive {@code boolean} value
   * @return {@code true} if {@code array[i] == target} for some value of {@code i}
   */
  public static boolean contains(boolean[] array, boolean target) {
    for (boolean value : array) {
      if (value == target) {
        return true;
      }
    }
    return false;
  }

  
Returns the index of the first appearance of the value target in array. 
Note: consider representing the array as a BitSet instead, and using BitSet.nextSetBit(int) or BitSet.nextClearBit(int). 
Params:
  • array – an array of boolean values, possibly empty
  • target – a primitive boolean value
Returns:the least index i for which array[i] == target, or -1 if no such index exists.
/**
   * Returns the index of the first appearance of the value {@code target} in {@code array}.
   *
   * <p><b>Note:</b> consider representing the array as a {@link java.util.BitSet} instead, and
   * using {@link java.util.BitSet#nextSetBit(int)} or {@link java.util.BitSet#nextClearBit(int)}.
   *
   * @param array an array of {@code boolean} values, possibly empty
   * @param target a primitive {@code boolean} value
   * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no
   *     such index exists.
   */
  public static int indexOf(boolean[] array, boolean target) {
    return indexOf(array, target, 0, array.length);
  }

  // TODO(kevinb): consider making this public
  private static int indexOf(boolean[] array, boolean target, int start, int end) {
    for (int i = start; i < end; i++) {
      if (array[i] == target) {
        return i;
      }
    }
    return -1;
  }

  
Returns the start position of the first occurrence of the specified target within array, or -1 if there is no such occurrence. 
More formally, returns the lowest index i such that Arrays.copyOfRange(array,
i, i + target.length) contains exactly the same elements as target. 
Params:
  • array – the array to search for the sequence target
  • target – the array to search for as a sub-sequence of array
/**
   * Returns the start position of the first occurrence of the specified {@code target} within
   * {@code array}, or {@code -1} if there is no such occurrence.
   *
   * <p>More formally, returns the lowest index {@code i} such that {@code Arrays.copyOfRange(array,
   * i, i + target.length)} contains exactly the same elements as {@code target}.
   *
   * @param array the array to search for the sequence {@code target}
   * @param target the array to search for as a sub-sequence of {@code array}
   */
  public static int indexOf(boolean[] array, boolean[] target) {
    checkNotNull(array, "array");
    checkNotNull(target, "target");
    if (target.length == 0) {
      return 0;
    }

    outer:
    for (int i = 0; i < array.length - target.length + 1; i++) {
      for (int j = 0; j < target.length; j++) {
        if (array[i + j] != target[j]) {
          continue outer;
        }
      }
      return i;
    }
    return -1;
  }

  
Returns the index of the last appearance of the value target in array. 
Params:
  • array – an array of boolean values, possibly empty
  • target – a primitive boolean value
Returns:the greatest index i for which array[i] == target, or -1 if no such index exists.
/**
   * Returns the index of the last appearance of the value {@code target} in {@code array}.
   *
   * @param array an array of {@code boolean} values, possibly empty
   * @param target a primitive {@code boolean} value
   * @return the greatest index {@code i} for which {@code array[i] == target}, or {@code -1} if no
   *     such index exists.
   */
  public static int lastIndexOf(boolean[] array, boolean target) {
    return lastIndexOf(array, target, 0, array.length);
  }

  // TODO(kevinb): consider making this public
  private static int lastIndexOf(boolean[] array, boolean target, int start, int end) {
    for (int i = end - 1; i >= start; i--) {
      if (array[i] == target) {
        return i;
      }
    }
    return -1;
  }

  
Returns the values from each provided array combined into a single array. For example, 
concat(new boolean[] {a, b}, new boolean[] {}, new boolean[] {c} returns the array {a,
b, c}. 
Params:
  • arrays – zero or more boolean arrays
Returns:a single array containing all the values from the source arrays, in order
/**
   * Returns the values from each provided array combined into a single array. For example, {@code
   * concat(new boolean[] {a, b}, new boolean[] {}, new boolean[] {c}} returns the array {@code {a,
   * b, c}}.
   *
   * @param arrays zero or more {@code boolean} arrays
   * @return a single array containing all the values from the source arrays, in order
   */
  public static boolean[] concat(boolean[]... arrays) {
    int length = 0;
    for (boolean[] array : arrays) {
      length += array.length;
    }
    boolean[] result = new boolean[length];
    int pos = 0;
    for (boolean[] array : arrays) {
      System.arraycopy(array, 0, result, pos, array.length);
      pos += array.length;
    }
    return result;
  }

  
Returns an array containing the same values as array, but guaranteed to be of a specified minimum length. If array already has a length of at least minLength, it is returned directly. Otherwise, a new array of size minLength + padding is returned, containing the values of array, and zeroes in the remaining places. 
Params:
  • array – the source array
  • minLength – the minimum length the returned array must guarantee
  • padding – an extra amount to "grow" the array by if growth is necessary
Throws:
Returns:an array containing the values of array, with guaranteed minimum length 
    minLength
/**
   * Returns an array containing the same values as {@code array}, but guaranteed to be of a
   * specified minimum length. If {@code array} already has a length of at least {@code minLength},
   * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is
   * returned, containing the values of {@code array}, and zeroes in the remaining places.
   *
   * @param array the source array
   * @param minLength the minimum length the returned array must guarantee
   * @param padding an extra amount to "grow" the array by if growth is necessary
   * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative
   * @return an array containing the values of {@code array}, with guaranteed minimum length {@code
   *     minLength}
   */
  public static boolean[] ensureCapacity(boolean[] array, int minLength, int padding) {
    checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
    checkArgument(padding >= 0, "Invalid padding: %s", padding);
    return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array;
  }

  
Returns a string containing the supplied boolean values separated by separator. For example, join("-", false, true, false) returns the string 
"false-true-false". 
Params:
  • separator – the text that should appear between consecutive values in the resulting string
    (but not at the start or end)
  • array – an array of boolean values, possibly empty
/**
   * Returns a string containing the supplied {@code boolean} values separated by {@code separator}.
   * For example, {@code join("-", false, true, false)} returns the string {@code
   * "false-true-false"}.
   *
   * @param separator the text that should appear between consecutive values in the resulting string
   *     (but not at the start or end)
   * @param array an array of {@code boolean} values, possibly empty
   */
  public static String join(String separator, boolean... array) {
    checkNotNull(separator);
    if (array.length == 0) {
      return "";
    }

    // For pre-sizing a builder, just get the right order of magnitude
    StringBuilder builder = new StringBuilder(array.length * 7);
    builder.append(array[0]);
    for (int i = 1; i < array.length; i++) {
      builder.append(separator).append(array[i]);
    }
    return builder.toString();
  }

  
Returns a comparator that compares two boolean arrays lexicographically. That is, it compares, using compare(boolean, boolean)), the first pair of values that follow any common prefix, or when one array is a prefix of the other, treats the shorter array as the lesser. For example, [] < [false] < [false, true] < [true]. 
The returned comparator is inconsistent with Object.equals(Object) (since arrays support only identity equality), but it is consistent with Arrays.equals(boolean[], boolean[]). 
Since:2.0
/**
   * Returns a comparator that compares two {@code boolean} arrays <a
   * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it
   * compares, using {@link #compare(boolean, boolean)}), the first pair of values that follow any
   * common prefix, or when one array is a prefix of the other, treats the shorter array as the
   * lesser. For example, {@code [] < [false] < [false, true] < [true]}.
   *
   * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
   * support only identity equality), but it is consistent with {@link Arrays#equals(boolean[],
   * boolean[])}.
   *
   * @since 2.0
   */
  public static Comparator<boolean[]> lexicographicalComparator() {
    return LexicographicalComparator.INSTANCE;
  }

  private enum LexicographicalComparator implements Comparator<boolean[]> {
    INSTANCE;

    @Override
    public int compare(boolean[] left, boolean[] right) {
      int minLength = Math.min(left.length, right.length);
      for (int i = 0; i < minLength; i++) {
        int result = Booleans.compare(left[i], right[i]);
        if (result != 0) {
          return result;
        }
      }
      return left.length - right.length;
    }

    @Override
    public String toString() {
      return "Booleans.lexicographicalComparator()";
    }
  }

  
Copies a collection of Boolean instances into a new array of primitive boolean values. 
Elements are copied from the argument collection as if by collection.toArray(). Calling this method is as thread-safe as calling that method. 
Note: consider representing the collection as a BitSet instead. 
Params:
  • collection – a collection of Boolean objects
Throws:
Returns:an array containing the same values as collection, in the same order, converted to primitives
/**
   * Copies a collection of {@code Boolean} instances into a new array of primitive {@code boolean}
   * values.
   *
   * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
   * Calling this method is as thread-safe as calling that method.
   *
   * <p><b>Note:</b> consider representing the collection as a {@link java.util.BitSet} instead.
   *
   * @param collection a collection of {@code Boolean} objects
   * @return an array containing the same values as {@code collection}, in the same order, converted
   *     to primitives
   * @throws NullPointerException if {@code collection} or any of its elements is null
   */
  public static boolean[] toArray(Collection<Boolean> collection) {
    if (collection instanceof BooleanArrayAsList) {
      return ((BooleanArrayAsList) collection).toBooleanArray();
    }

    Object[] boxedArray = collection.toArray();
    int len = boxedArray.length;
    boolean[] array = new boolean[len];
    for (int i = 0; i < len; i++) {
      // checkNotNull for GWT (do not optimize)
      array[i] = (Boolean) checkNotNull(boxedArray[i]);
    }
    return array;
  }

  
Returns a fixed-size list backed by the specified array, similar to Arrays.asList(Object[]). The list supports List.set(int, Object), but any attempt to set a value to null will result in a NullPointerException. 
The returned list maintains the values, but not the identities, of Boolean objects written to or read from it. For example, whether list.get(0) == list.get(0) is true for the returned list is unspecified. 
Params:
  • backingArray – the array to back the list
Returns:a list view of the array
/**
   * Returns a fixed-size list backed by the specified array, similar to {@link
   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
   * set a value to {@code null} will result in a {@link NullPointerException}.
   *
   * <p>The returned list maintains the values, but not the identities, of {@code Boolean} objects
   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
   * the returned list is unspecified.
   *
   * @param backingArray the array to back the list
   * @return a list view of the array
   */
  public static List<Boolean> asList(boolean... backingArray) {
    if (backingArray.length == 0) {
      return Collections.emptyList();
    }
    return new BooleanArrayAsList(backingArray);
  }

  @GwtCompatible
  private static class BooleanArrayAsList extends AbstractList<Boolean>
      implements RandomAccess, Serializable {
    final boolean[] array;
    final int start;
    final int end;

    BooleanArrayAsList(boolean[] array) {
      this(array, 0, array.length);
    }

    BooleanArrayAsList(boolean[] array, int start, int end) {
      this.array = array;
      this.start = start;
      this.end = end;
    }

    @Override
    public int size() {
      return end - start;
    }

    @Override
    public boolean isEmpty() {
      return false;
    }

    @Override
    public Boolean get(int index) {
      checkElementIndex(index, size());
      return array[start + index];
    }

    @Override
    public boolean contains(Object target) {
      // Overridden to prevent a ton of boxing
      return (target instanceof Boolean)
          && Booleans.indexOf(array, (Boolean) target, start, end) != -1;
    }

    @Override
    public int indexOf(Object target) {
      // Overridden to prevent a ton of boxing
      if (target instanceof Boolean) {
        int i = Booleans.indexOf(array, (Boolean) target, start, end);
        if (i >= 0) {
          return i - start;
        }
      }
      return -1;
    }

    @Override
    public int lastIndexOf(Object target) {
      // Overridden to prevent a ton of boxing
      if (target instanceof Boolean) {
        int i = Booleans.lastIndexOf(array, (Boolean) target, start, end);
        if (i >= 0) {
          return i - start;
        }
      }
      return -1;
    }

    @Override
    public Boolean set(int index, Boolean element) {
      checkElementIndex(index, size());
      boolean oldValue = array[start + index];
      // checkNotNull for GWT (do not optimize)
      array[start + index] = checkNotNull(element);
      return oldValue;
    }

    @Override
    public List<Boolean> subList(int fromIndex, int toIndex) {
      int size = size();
      checkPositionIndexes(fromIndex, toIndex, size);
      if (fromIndex == toIndex) {
        return Collections.emptyList();
      }
      return new BooleanArrayAsList(array, start + fromIndex, start + toIndex);
    }

    @Override
    public boolean equals(@Nullable Object object) {
      if (object == this) {
        return true;
      }
      if (object instanceof BooleanArrayAsList) {
        BooleanArrayAsList that = (BooleanArrayAsList) object;
        int size = size();
        if (that.size() != size) {
          return false;
        }
        for (int i = 0; i < size; i++) {
          if (array[start + i] != that.array[that.start + i]) {
            return false;
          }
        }
        return true;
      }
      return super.equals(object);
    }

    @Override
    public int hashCode() {
      int result = 1;
      for (int i = start; i < end; i++) {
        result = 31 * result + Booleans.hashCode(array[i]);
      }
      return result;
    }

    @Override
    public String toString() {
      StringBuilder builder = new StringBuilder(size() * 7);
      builder.append(array[start] ? "[true" : "[false");
      for (int i = start + 1; i < end; i++) {
        builder.append(array[i] ? ", true" : ", false");
      }
      return builder.append(']').toString();
    }

    boolean[] toBooleanArray() {
      return Arrays.copyOfRange(array, start, end);
    }

    private static final long serialVersionUID = 0;
  }

  
Returns the number of values that are true. 
Since:16.0
/**
   * Returns the number of {@code values} that are {@code true}.
   *
   * @since 16.0
   */
  @Beta
  public static int countTrue(boolean... values) {
    int count = 0;
    for (boolean value : values) {
      if (value) {
        count++;
      }
    }
    return count;
  }

  
Reverses the elements of array. This is equivalent to 
Collections.reverse(Booleans.asList(array)), but is likely to be more efficient. 
Since:23.1
/**
   * Reverses the elements of {@code array}. This is equivalent to {@code
   * Collections.reverse(Booleans.asList(array))}, but is likely to be more efficient.
   *
   * @since 23.1
   */
  public static void reverse(boolean[] array) {
    checkNotNull(array);
    reverse(array, 0, array.length);
  }

  
Reverses the elements of array between fromIndex inclusive and toIndex exclusive. This is equivalent to 
Collections.reverse(Booleans.asList(array).subList(fromIndex, toIndex)), but is likely to be more efficient. 
Throws:
Since:23.1
/**
   * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
   * exclusive. This is equivalent to {@code
   * Collections.reverse(Booleans.asList(array).subList(fromIndex, toIndex))}, but is likely to be
   * more efficient.
   *
   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
   *     {@code toIndex > fromIndex}
   * @since 23.1
   */
  public static void reverse(boolean[] array, int fromIndex, int toIndex) {
    checkNotNull(array);
    checkPositionIndexes(fromIndex, toIndex, array.length);
    for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
      boolean tmp = array[i];
      array[i] = array[j];
      array[j] = tmp;
    }
  }
}