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 static java.lang.Double.NEGATIVE_INFINITY;
import static java.lang.Double.POSITIVE_INFINITY;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Converter;
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 java.util.Spliterator;
import java.util.Spliterators;
import org.checkerframework.checker.nullness.qual.Nullable;


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

Author:Kevin Bourrillion
Since:1.0
/**
 * Static utility methods pertaining to {@code double} primitives, that are not already found in
 * either {@link Double} 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(emulated = true)
public final class Doubles {
  private Doubles() {}

  
The number of bytes required to represent a primitive double value. 
Java 8 users: use Double.BYTES instead. 
Since:10.0
/**
   * The number of bytes required to represent a primitive {@code double} value.
   *
   * <p><b>Java 8 users:</b> use {@link Double#BYTES} instead.
   *
   * @since 10.0
   */
  public static final int BYTES = Double.SIZE / Byte.SIZE;

  
Returns a hash code for value; equal to the result of invoking ((Double)
value).hashCode(). 
Java 8 users: use Double.hashCode(double) instead. 
Params:
  • value – a primitive double value
Returns:a hash code for the value
/**
   * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Double)
   * value).hashCode()}.
   *
   * <p><b>Java 8 users:</b> use {@link Double#hashCode(double)} instead.
   *
   * @param value a primitive {@code double} value
   * @return a hash code for the value
   */
  public static int hashCode(double value) {
    return ((Double) value).hashCode();
    // TODO(kevinb): do it this way when we can (GWT problem):
    // long bits = Double.doubleToLongBits(value);
    // return (int) (bits ^ (bits >>> 32));
  }

  
Compares the two specified double values. The sign of the value returned is the same as that of ((Double) a).compareTo(b). As with that method, NaN is treated as greater than all other values, and 0.0 > -0.0. 
Note: this method simply delegates to the JDK method Double.compare. It is provided for consistency with the other primitive types, whose compare methods were not added to the JDK until JDK 7. 
Params:
  • a – the first double to compare
  • b – the second double to compare
Returns:a negative value if a is less than b; a positive value if a is greater than b; or zero if they are equal
/**
   * Compares the two specified {@code double} values. The sign of the value returned is the same as
   * that of <code>((Double) a).{@linkplain Double#compareTo compareTo}(b)</code>. As with that
   * method, {@code NaN} is treated as greater than all other values, and {@code 0.0 > -0.0}.
   *
   * <p><b>Note:</b> this method simply delegates to the JDK method {@link Double#compare}. It is
   * provided for consistency with the other primitive types, whose compare methods were not added
   * to the JDK until JDK 7.
   *
   * @param a the first {@code double} to compare
   * @param b the second {@code double} to compare
   * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
   *     greater than {@code b}; or zero if they are equal
   */
  public static int compare(double a, double b) {
    return Double.compare(a, b);
  }

  
Returns true if value represents a real number. This is equivalent to, but not necessarily implemented as, !(Double.isInfinite(value) || Double.isNaN(value)). 
Java 8 users: use Double.isFinite(double) instead. 
Since:10.0
/**
   * Returns {@code true} if {@code value} represents a real number. This is equivalent to, but not
   * necessarily implemented as, {@code !(Double.isInfinite(value) || Double.isNaN(value))}.
   *
   * <p><b>Java 8 users:</b> use {@link Double#isFinite(double)} instead.
   *
   * @since 10.0
   */
  public static boolean isFinite(double value) {
    return NEGATIVE_INFINITY < value && value < POSITIVE_INFINITY;
  }

  
Returns true if target is present as an element anywhere in array. Note that this always returns false when target is NaN. 
Params:
  • array – an array of double values, possibly empty
  • target – a primitive double 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}. Note
   * that this always returns {@code false} when {@code target} is {@code NaN}.
   *
   * @param array an array of {@code double} values, possibly empty
   * @param target a primitive {@code double} value
   * @return {@code true} if {@code array[i] == target} for some value of {@code i}
   */
  public static boolean contains(double[] array, double target) {
    for (double value : array) {
      if (value == target) {
        return true;
      }
    }
    return false;
  }

  
Returns the index of the first appearance of the value target in array. Note that this always returns -1 when target is NaN. 
Params:
  • array – an array of double values, possibly empty
  • target – a primitive double 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}. Note
   * that this always returns {@code -1} when {@code target} is {@code NaN}.
   *
   * @param array an array of {@code double} values, possibly empty
   * @param target a primitive {@code double} 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(double[] array, double target) {
    return indexOf(array, target, 0, array.length);
  }

  // TODO(kevinb): consider making this public
  private static int indexOf(double[] array, double 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. 
Note that this always returns -1 when target contains NaN. 
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}.
   *
   * <p>Note that this always returns {@code -1} when {@code target} contains {@code NaN}.
   *
   * @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(double[] array, double[] 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. Note that this always returns -1 when target is NaN. 
Params:
  • array – an array of double values, possibly empty
  • target – a primitive double 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}. Note
   * that this always returns {@code -1} when {@code target} is {@code NaN}.
   *
   * @param array an array of {@code double} values, possibly empty
   * @param target a primitive {@code double} 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(double[] array, double target) {
    return lastIndexOf(array, target, 0, array.length);
  }

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

  
Returns the least value present in array, using the same rules of comparison as Math.min(double, double). 
Params:
  • array – a nonempty array of double values
Throws:
Returns:the value present in array that is less than or equal to every other value in the array
/**
   * Returns the least value present in {@code array}, using the same rules of comparison as {@link
   * Math#min(double, double)}.
   *
   * @param array a <i>nonempty</i> array of {@code double} values
   * @return the value present in {@code array} that is less than or equal to every other value in
   *     the array
   * @throws IllegalArgumentException if {@code array} is empty
   */
  public static double min(double... array) {
    checkArgument(array.length > 0);
    double min = array[0];
    for (int i = 1; i < array.length; i++) {
      min = Math.min(min, array[i]);
    }
    return min;
  }

  
Returns the greatest value present in array, using the same rules of comparison as Math.max(double, double). 
Params:
  • array – a nonempty array of double values
Throws:
Returns:the value present in array that is greater than or equal to every other value in the array
/**
   * Returns the greatest value present in {@code array}, using the same rules of comparison as
   * {@link Math#max(double, double)}.
   *
   * @param array a <i>nonempty</i> array of {@code double} values
   * @return the value present in {@code array} that is greater than or equal to every other value
   *     in the array
   * @throws IllegalArgumentException if {@code array} is empty
   */
  public static double max(double... array) {
    checkArgument(array.length > 0);
    double max = array[0];
    for (int i = 1; i < array.length; i++) {
      max = Math.max(max, array[i]);
    }
    return max;
  }

  
Returns the value nearest to value which is within the closed range [min..max]. 
If value is within the range [min..max], value is returned unchanged. If value is less than min, min is returned, and if 
value is greater than max, max is returned. 
Params:
  • value – the double value to constrain
  • min – the lower bound (inclusive) of the range to constrain value to
  • max – the upper bound (inclusive) of the range to constrain value to
Throws:
Since:21.0
/**
   * Returns the value nearest to {@code value} which is within the closed range {@code [min..max]}.
   *
   * <p>If {@code value} is within the range {@code [min..max]}, {@code value} is returned
   * unchanged. If {@code value} is less than {@code min}, {@code min} is returned, and if {@code
   * value} is greater than {@code max}, {@code max} is returned.
   *
   * @param value the {@code double} value to constrain
   * @param min the lower bound (inclusive) of the range to constrain {@code value} to
   * @param max the upper bound (inclusive) of the range to constrain {@code value} to
   * @throws IllegalArgumentException if {@code min > max}
   * @since 21.0
   */
  @Beta
  public static double constrainToRange(double value, double min, double max) {
    checkArgument(min <= max, "min (%s) must be less than or equal to max (%s)", min, max);
    return Math.min(Math.max(value, min), max);
  }

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

  private static final class DoubleConverter extends Converter<String, Double>
      implements Serializable {
    static final DoubleConverter INSTANCE = new DoubleConverter();

    @Override
    protected Double doForward(String value) {
      return Double.valueOf(value);
    }

    @Override
    protected String doBackward(Double value) {
      return value.toString();
    }

    @Override
    public String toString() {
      return "Doubles.stringConverter()";
    }

    private Object readResolve() {
      return INSTANCE;
    }

    private static final long serialVersionUID = 1;
  }

  
Returns a serializable converter object that converts between strings and doubles using Double.valueOf and Double.toString(). 
Since:16.0
/**
   * Returns a serializable converter object that converts between strings and doubles using {@link
   * Double#valueOf} and {@link Double#toString()}.
   *
   * @since 16.0
   */
  @Beta
  public static Converter<String, Double> stringConverter() {
    return DoubleConverter.INSTANCE;
  }

  
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 double[] ensureCapacity(double[] 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 double values, converted to strings as specified by Double.toString(double), and separated by separator. For example, join("-", 1.0, 2.0, 3.0) returns the string "1.0-2.0-3.0". 
Note that Double.toString(double) formats double differently in GWT sometimes. In the previous example, it returns the string "1-2-3". 
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 double values, possibly empty
/**
   * Returns a string containing the supplied {@code double} values, converted to strings as
   * specified by {@link Double#toString(double)}, and separated by {@code separator}. For example,
   * {@code join("-", 1.0, 2.0, 3.0)} returns the string {@code "1.0-2.0-3.0"}.
   *
   * <p>Note that {@link Double#toString(double)} formats {@code double} differently in GWT
   * sometimes. In the previous example, it returns the string {@code "1-2-3"}.
   *
   * @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 double} values, possibly empty
   */
  public static String join(String separator, double... 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 * 12);
    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 double arrays lexicographically. That is, it compares, using compare(double, double)), 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, [] < [1.0] < [1.0, 2.0] < [2.0]. 
The returned comparator is inconsistent with Object.equals(Object) (since arrays support only identity equality), but it is consistent with Arrays.equals(double[], double[]). 
Since:2.0
/**
   * Returns a comparator that compares two {@code double} arrays <a
   * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it
   * compares, using {@link #compare(double, double)}), 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 [] < [1.0] < [1.0, 2.0] < [2.0]}.
   *
   * <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(double[],
   * double[])}.
   *
   * @since 2.0
   */
  public static Comparator<double[]> lexicographicalComparator() {
    return LexicographicalComparator.INSTANCE;
  }

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

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

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

  
Sorts the elements of array in descending order. 
Note that this method uses the total order imposed by Double.compare, which treats all NaN values as equal and 0.0 as greater than -0.0. 
Since:23.1
/**
   * Sorts the elements of {@code array} in descending order.
   *
   * <p>Note that this method uses the total order imposed by {@link Double#compare}, which treats
   * all NaN values as equal and 0.0 as greater than -0.0.
   *
   * @since 23.1
   */
  public static void sortDescending(double[] array) {
    checkNotNull(array);
    sortDescending(array, 0, array.length);
  }

  
Sorts the elements of array between fromIndex inclusive and toIndex exclusive in descending order. 
Note that this method uses the total order imposed by Double.compare, which treats all NaN values as equal and 0.0 as greater than -0.0. 
Since:23.1
/**
   * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
   * exclusive in descending order.
   *
   * <p>Note that this method uses the total order imposed by {@link Double#compare}, which treats
   * all NaN values as equal and 0.0 as greater than -0.0.
   *
   * @since 23.1
   */
  public static void sortDescending(double[] array, int fromIndex, int toIndex) {
    checkNotNull(array);
    checkPositionIndexes(fromIndex, toIndex, array.length);
    Arrays.sort(array, fromIndex, toIndex);
    reverse(array, fromIndex, toIndex);
  }

  
Reverses the elements of array. This is equivalent to 
Collections.reverse(Doubles.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(Doubles.asList(array))}, but is likely to be more efficient.
   *
   * @since 23.1
   */
  public static void reverse(double[] 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(Doubles.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(Doubles.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(double[] array, int fromIndex, int toIndex) {
    checkNotNull(array);
    checkPositionIndexes(fromIndex, toIndex, array.length);
    for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
      double tmp = array[i];
      array[i] = array[j];
      array[j] = tmp;
    }
  }

  
Returns an array containing each value of collection, converted to a double value in the manner of Number.doubleValue. 
Elements are copied from the argument collection as if by collection.toArray(). Calling this method is as thread-safe as calling that method. 
Params:
  • collection – a collection of Number instances
Throws:
Returns:an array containing the same values as collection, in the same order, converted to primitives
Since:1.0 (parameter was Collection<Double> before 12.0)
/**
   * Returns an array containing each value of {@code collection}, converted to a {@code double}
   * value in the manner of {@link Number#doubleValue}.
   *
   * <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.
   *
   * @param collection a collection of {@code Number} instances
   * @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
   * @since 1.0 (parameter was {@code Collection<Double>} before 12.0)
   */
  public static double[] toArray(Collection<? extends Number> collection) {
    if (collection instanceof DoubleArrayAsList) {
      return ((DoubleArrayAsList) collection).toDoubleArray();
    }

    Object[] boxedArray = collection.toArray();
    int len = boxedArray.length;
    double[] array = new double[len];
    for (int i = 0; i < len; i++) {
      // checkNotNull for GWT (do not optimize)
      array[i] = ((Number) checkNotNull(boxedArray[i])).doubleValue();
    }
    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 Double objects written to or read from it. For example, whether list.get(0) == list.get(0) is true for the returned list is unspecified. 
The returned list may have unexpected behavior if it contains NaN, or if NaN is used as a parameter to any of its methods. 
Note: when possible, you should represent your data as an ImmutableDoubleArray instead, which has an asList view. 
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 Double} 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.
   *
   * <p>The returned list may have unexpected behavior if it contains {@code NaN}, or if {@code NaN}
   * is used as a parameter to any of its methods.
   *
   * <p><b>Note:</b> when possible, you should represent your data as an {@link
   * ImmutableDoubleArray} instead, which has an {@link ImmutableDoubleArray#asList asList} view.
   *
   * @param backingArray the array to back the list
   * @return a list view of the array
   */
  public static List<Double> asList(double... backingArray) {
    if (backingArray.length == 0) {
      return Collections.emptyList();
    }
    return new DoubleArrayAsList(backingArray);
  }

  @GwtCompatible
  private static class DoubleArrayAsList extends AbstractList<Double>
      implements RandomAccess, Serializable {
    final double[] array;
    final int start;
    final int end;

    DoubleArrayAsList(double[] array) {
      this(array, 0, array.length);
    }

    DoubleArrayAsList(double[] 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 Double get(int index) {
      checkElementIndex(index, size());
      return array[start + index];
    }

    @Override
    public Spliterator.OfDouble spliterator() {
      return Spliterators.spliterator(array, start, end, 0);
    }

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

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

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

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

    @Override
    public boolean equals(@Nullable Object object) {
      if (object == this) {
        return true;
      }
      if (object instanceof DoubleArrayAsList) {
        DoubleArrayAsList that = (DoubleArrayAsList) 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 + Doubles.hashCode(array[i]);
      }
      return result;
    }

    @Override
    public String toString() {
      StringBuilder builder = new StringBuilder(size() * 12);
      builder.append('[').append(array[start]);
      for (int i = start + 1; i < end; i++) {
        builder.append(", ").append(array[i]);
      }
      return builder.append(']').toString();
    }

    double[] toDoubleArray() {
      return Arrays.copyOfRange(array, start, end);
    }

    private static final long serialVersionUID = 0;
  }

  
This is adapted from the regex suggested by Double.valueOf(String) for prevalidating inputs. All valid inputs must pass this regex, but it's semantically fine if not all inputs that pass this regex are valid -- only a performance hit is incurred, not a semantics bug. 
/**
   * This is adapted from the regex suggested by {@link Double#valueOf(String)} for prevalidating
   * inputs. All valid inputs must pass this regex, but it's semantically fine if not all inputs
   * that pass this regex are valid -- only a performance hit is incurred, not a semantics bug.
   */
  @GwtIncompatible // regular expressions
  static final
  java.util.regex.Pattern
      FLOATING_POINT_PATTERN = fpPattern();

  @GwtIncompatible // regular expressions
  private static
  java.util.regex.Pattern
      fpPattern() {
    /*
     * We use # instead of * for possessive quantifiers. This lets us strip them out when building
     * the regex for RE2 (which doesn't support them) but leave them in when building it for
     * java.util.regex (where we want them in order to avoid catastrophic backtracking).
     */
    String decimal = "(?:\\d+#(?:\\.\\d*#)?|\\.\\d+#)";
    String completeDec = decimal + "(?:[eE][+-]?\\d+#)?[fFdD]?";
    String hex = "(?:[0-9a-fA-F]+#(?:\\.[0-9a-fA-F]*#)?|\\.[0-9a-fA-F]+#)";
    String completeHex = "0[xX]" + hex + "[pP][+-]?\\d+#[fFdD]?";
    String fpPattern = "[+-]?(?:NaN|Infinity|" + completeDec + "|" + completeHex + ")";
    fpPattern =
        fpPattern.replace(
            "#",
            "+"
            );
    return
    java.util.regex.Pattern
        .compile(fpPattern);
  }

  
Parses the specified string as a double-precision floating point value. The ASCII character '-' ('\u002D') is recognized as the minus sign.

Unlike Double.parseDouble(String), this method returns null instead of throwing an exception if parsing fails. Valid inputs are exactly those accepted by Double.valueOf(String), except that leading and trailing whitespace is not permitted. 
This implementation is likely to be faster than Double.parseDouble if many failures are expected. 
Params:
  • string – the string representation of a double value
Returns:the floating point value represented by string, or null if 
    string has a length of zero or cannot be parsed as a double value
Since:14.0
/**
   * Parses the specified string as a double-precision floating point value. The ASCII character
   * {@code '-'} (<code>'&#92;u002D'</code>) is recognized as the minus sign.
   *
   * <p>Unlike {@link Double#parseDouble(String)}, this method returns {@code null} instead of
   * throwing an exception if parsing fails. Valid inputs are exactly those accepted by {@link
   * Double#valueOf(String)}, except that leading and trailing whitespace is not permitted.
   *
   * <p>This implementation is likely to be faster than {@code Double.parseDouble} if many failures
   * are expected.
   *
   * @param string the string representation of a {@code double} value
   * @return the floating point value represented by {@code string}, or {@code null} if {@code
   *     string} has a length of zero or cannot be parsed as a {@code double} value
   * @since 14.0
   */
  @Beta
  @GwtIncompatible // regular expressions
  public static @Nullable Double tryParse(String string) {
    if (FLOATING_POINT_PATTERN.matcher(string).matches()) {
      // TODO(lowasser): could be potentially optimized, but only with
      // extensive testing
      try {
        return Double.parseDouble(string);
      } catch (NumberFormatException e) {
        // Double.parseDouble has changed specs several times, so fall through
        // gracefully
      }
    }
    return null;
  }
}