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) 2017 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.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Preconditions;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.CheckReturnValue;
import com.google.errorprone.annotations.Immutable;
import java.io.Serializable;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.RandomAccess;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.DoubleConsumer;
import java.util.stream.DoubleStream;
import org.checkerframework.checker.nullness.qual.Nullable;


An immutable array of double values, with an API resembling List. 
Advantages compared to double[]: 
    
  
  • All the many well-known advantages of immutability (read Effective Java, second
      edition, Item 15).
  
  • Has the value-based (not identity-based) equals, hashCode, and toString behavior you expect. 
  • Offers useful operations beyond just get and length, so you don't have to hunt through classes like Arrays and Doubles for them. 
  • Supports a copy-free subArray view, so methods that accept this type don't need to add overloads that accept start and end indexes. 
  • Can be streamed without "breaking the chain": foo.getBarDoubles().stream().... 
  • Access to all collection-based utilities via asList (though at the cost of allocating garbage). 


Disadvantages compared to double[]: 
    
  
  • Memory footprint has a fixed overhead (about 24 bytes per instance).
  
  • Some construction use cases force the data to be copied (though several construction
      APIs are offered that don't).
  
  • Can't be passed directly to methods that expect double[] (though the most common utilities do have replacements here). 
  • Dependency on com.google.common / Guava. 


Advantages compared to ImmutableList
<Double>: 
    
  
  • Improved memory compactness and locality.
  
  • Can be queried without allocating garbage.
  
  • Access to DoubleStream features (like DoubleStream.sum) using 
      stream() instead of the awkward stream().mapToDouble(v -> v). 


Disadvantages compared to ImmutableList<Double>: 
    
  
  • Can't be passed directly to methods that expect Iterable, Collection, or List (though the most common utilities do have replacements here, and there is a lazy asList view). 


Since:22.0
/**
 * An immutable array of {@code double} values, with an API resembling {@link List}.
 *
 * <p>Advantages compared to {@code double[]}:
 *
 * <ul>
 *   <li>All the many well-known advantages of immutability (read <i>Effective Java</i>, second
 *       edition, Item 15).
 *   <li>Has the value-based (not identity-based) {@link #equals}, {@link #hashCode}, and {@link
 *       #toString} behavior you expect.
 *   <li>Offers useful operations beyond just {@code get} and {@code length}, so you don't have to
 *       hunt through classes like {@link Arrays} and {@link Doubles} for them.
 *   <li>Supports a copy-free {@link #subArray} view, so methods that accept this type don't need to
 *       add overloads that accept start and end indexes.
 *   <li>Can be streamed without "breaking the chain": {@code foo.getBarDoubles().stream()...}.
 *   <li>Access to all collection-based utilities via {@link #asList} (though at the cost of
 *       allocating garbage).
 * </ul>
 *
 * <p>Disadvantages compared to {@code double[]}:
 *
 * <ul>
 *   <li>Memory footprint has a fixed overhead (about 24 bytes per instance).
 *   <li><i>Some</i> construction use cases force the data to be copied (though several construction
 *       APIs are offered that don't).
 *   <li>Can't be passed directly to methods that expect {@code double[]} (though the most common
 *       utilities do have replacements here).
 *   <li>Dependency on {@code com.google.common} / Guava.
 * </ul>
 *
 * <p>Advantages compared to {@link com.google.common.collect.ImmutableList ImmutableList}{@code
 * <Double>}:
 *
 * <ul>
 *   <li>Improved memory compactness and locality.
 *   <li>Can be queried without allocating garbage.
 *   <li>Access to {@code DoubleStream} features (like {@link DoubleStream#sum}) using {@code
 *       stream()} instead of the awkward {@code stream().mapToDouble(v -> v)}.
 * </ul>
 *
 * <p>Disadvantages compared to {@code ImmutableList<Double>}:
 *
 * <ul>
 *   <li>Can't be passed directly to methods that expect {@code Iterable}, {@code Collection}, or
 *       {@code List} (though the most common utilities do have replacements here, and there is a
 *       lazy {@link #asList} view).
 * </ul>
 *
 * @since 22.0
 */
@Beta
@GwtCompatible
@Immutable
public final class ImmutableDoubleArray implements Serializable {
  private static final ImmutableDoubleArray EMPTY = new ImmutableDoubleArray(new double[0]);

  
Returns the empty array. 
/** Returns the empty array. */
  public static ImmutableDoubleArray of() {
    return EMPTY;
  }

  
Returns an immutable array containing a single value. 
/** Returns an immutable array containing a single value. */
  public static ImmutableDoubleArray of(double e0) {
    return new ImmutableDoubleArray(new double[] {e0});
  }

  
Returns an immutable array containing the given values, in order. 
/** Returns an immutable array containing the given values, in order. */
  public static ImmutableDoubleArray of(double e0, double e1) {
    return new ImmutableDoubleArray(new double[] {e0, e1});
  }

  
Returns an immutable array containing the given values, in order. 
/** Returns an immutable array containing the given values, in order. */
  public static ImmutableDoubleArray of(double e0, double e1, double e2) {
    return new ImmutableDoubleArray(new double[] {e0, e1, e2});
  }

  
Returns an immutable array containing the given values, in order. 
/** Returns an immutable array containing the given values, in order. */
  public static ImmutableDoubleArray of(double e0, double e1, double e2, double e3) {
    return new ImmutableDoubleArray(new double[] {e0, e1, e2, e3});
  }

  
Returns an immutable array containing the given values, in order. 
/** Returns an immutable array containing the given values, in order. */
  public static ImmutableDoubleArray of(double e0, double e1, double e2, double e3, double e4) {
    return new ImmutableDoubleArray(new double[] {e0, e1, e2, e3, e4});
  }

  
Returns an immutable array containing the given values, in order. 
/** Returns an immutable array containing the given values, in order. */
  public static ImmutableDoubleArray of(
      double e0, double e1, double e2, double e3, double e4, double e5) {
    return new ImmutableDoubleArray(new double[] {e0, e1, e2, e3, e4, e5});
  }

  // TODO(kevinb): go up to 11?

  
Returns an immutable array containing the given values, in order.

The array rest must not be longer than Integer.MAX_VALUE - 1. 
/**
   * Returns an immutable array containing the given values, in order.
   *
   * <p>The array {@code rest} must not be longer than {@code Integer.MAX_VALUE - 1}.
   */
  // Use (first, rest) so that `of(someDoubleArray)` won't compile (they should use copyOf), which
  // is okay since we have to copy the just-created array anyway.
  public static ImmutableDoubleArray of(double first, double... rest) {
    checkArgument(
        rest.length <= Integer.MAX_VALUE - 1,
        "the total number of elements must fit in an int");
    double[] array = new double[rest.length + 1];
    array[0] = first;
    System.arraycopy(rest, 0, array, 1, rest.length);
    return new ImmutableDoubleArray(array);
  }

  
Returns an immutable array containing the given values, in order. 
/** Returns an immutable array containing the given values, in order. */
  public static ImmutableDoubleArray copyOf(double[] values) {
    return values.length == 0
        ? EMPTY
        : new ImmutableDoubleArray(Arrays.copyOf(values, values.length));
  }

  
Returns an immutable array containing the given values, in order. 
/** Returns an immutable array containing the given values, in order. */
  public static ImmutableDoubleArray copyOf(Collection<Double> values) {
    return values.isEmpty() ? EMPTY : new ImmutableDoubleArray(Doubles.toArray(values));
  }

  
Returns an immutable array containing the given values, in order.

Performance note: this method delegates to copyOf(Collection<Double>) if 
values is a Collection. Otherwise it creates a builder and uses Builder.addAll(Iterable<Double>), with all the performance implications associated with that. 
/**
   * Returns an immutable array containing the given values, in order.
   *
   * <p><b>Performance note:</b> this method delegates to {@link #copyOf(Collection)} if {@code
   * values} is a {@link Collection}. Otherwise it creates a {@link #builder} and uses {@link
   * Builder#addAll(Iterable)}, with all the performance implications associated with that.
   */
  public static ImmutableDoubleArray copyOf(Iterable<Double> values) {
    if (values instanceof Collection) {
      return copyOf((Collection<Double>) values);
    }
    return builder().addAll(values).build();
  }

  
Returns an immutable array containing all the values from stream, in order. 
/** Returns an immutable array containing all the values from {@code stream}, in order. */
  public static ImmutableDoubleArray copyOf(DoubleStream stream) {
    // Note this uses very different growth behavior from copyOf(Iterable) and the builder.
    double[] array = stream.toArray();
    return (array.length == 0) ? EMPTY : new ImmutableDoubleArray(array);
  }

  
Returns a new, empty builder for ImmutableDoubleArray instances, sized to hold up to initialCapacity values without resizing. The returned builder is not thread-safe. 
Performance note: When feasible, initialCapacity should be the exact number of values that will be added, if that knowledge is readily available. It is better to guess a value slightly too high than slightly too low. If the value is not exact, the ImmutableDoubleArray that is built will very likely occupy more memory than strictly necessary; to trim memory usage, build using builder.build().trimmed(). 
/**
   * Returns a new, empty builder for {@link ImmutableDoubleArray} instances, sized to hold up to
   * {@code initialCapacity} values without resizing. The returned builder is not thread-safe.
   *
   * <p><b>Performance note:</b> When feasible, {@code initialCapacity} should be the exact number
   * of values that will be added, if that knowledge is readily available. It is better to guess a
   * value slightly too high than slightly too low. If the value is not exact, the {@link
   * ImmutableDoubleArray} that is built will very likely occupy more memory than strictly
   * necessary; to trim memory usage, build using {@code builder.build().trimmed()}.
   */
  public static Builder builder(int initialCapacity) {
    checkArgument(initialCapacity >= 0, "Invalid initialCapacity: %s", initialCapacity);
    return new Builder(initialCapacity);
  }

  
Returns a new, empty builder for ImmutableDoubleArray instances, with a default initial capacity. The returned builder is not thread-safe. 
Performance note: The ImmutableDoubleArray that is built will very likely occupy more memory than necessary; to trim memory usage, build using 
builder.build().trimmed(). 
/**
   * Returns a new, empty builder for {@link ImmutableDoubleArray} instances, with a default initial
   * capacity. The returned builder is not thread-safe.
   *
   * <p><b>Performance note:</b> The {@link ImmutableDoubleArray} that is built will very likely
   * occupy more memory than necessary; to trim memory usage, build using {@code
   * builder.build().trimmed()}.
   */
  public static Builder builder() {
    return new Builder(10);
  }

  
A builder for ImmutableDoubleArray instances; obtained using ImmutableDoubleArray.builder. 
/**
   * A builder for {@link ImmutableDoubleArray} instances; obtained using {@link
   * ImmutableDoubleArray#builder}.
   */
  @CanIgnoreReturnValue
  public static final class Builder {
    private double[] array;
    private int count = 0; // <= array.length

    Builder(int initialCapacity) {
      array = new double[initialCapacity];
    }

    
Appends value to the end of the values the built ImmutableDoubleArray will contain. 
/**
     * Appends {@code value} to the end of the values the built {@link ImmutableDoubleArray} will
     * contain.
     */
    public Builder add(double value) {
      ensureRoomFor(1);
      array[count] = value;
      count += 1;
      return this;
    }

    
Appends values, in order, to the end of the values the built ImmutableDoubleArray will contain. 
/**
     * Appends {@code values}, in order, to the end of the values the built {@link
     * ImmutableDoubleArray} will contain.
     */
    public Builder addAll(double[] values) {
      ensureRoomFor(values.length);
      System.arraycopy(values, 0, array, count, values.length);
      count += values.length;
      return this;
    }

    
Appends values, in order, to the end of the values the built ImmutableDoubleArray will contain. 
/**
     * Appends {@code values}, in order, to the end of the values the built {@link
     * ImmutableDoubleArray} will contain.
     */
    public Builder addAll(Iterable<Double> values) {
      if (values instanceof Collection) {
        return addAll((Collection<Double>) values);
      }
      for (Double value : values) {
        add(value);
      }
      return this;
    }

    
Appends values, in order, to the end of the values the built ImmutableDoubleArray will contain. 
/**
     * Appends {@code values}, in order, to the end of the values the built {@link
     * ImmutableDoubleArray} will contain.
     */
    public Builder addAll(Collection<Double> values) {
      ensureRoomFor(values.size());
      for (Double value : values) {
        array[count++] = value;
      }
      return this;
    }

    
Appends all values from stream, in order, to the end of the values the built ImmutableDoubleArray will contain. 
/**
     * Appends all values from {@code stream}, in order, to the end of the values the built {@link
     * ImmutableDoubleArray} will contain.
     */
    public Builder addAll(DoubleStream stream) {
      Spliterator.OfDouble spliterator = stream.spliterator();
      long size = spliterator.getExactSizeIfKnown();
      if (size > 0) { // known *and* nonempty
        ensureRoomFor(Ints.saturatedCast(size));
      }
      spliterator.forEachRemaining((DoubleConsumer) this::add);
      return this;
    }

    
Appends values, in order, to the end of the values the built ImmutableDoubleArray will contain. 
/**
     * Appends {@code values}, in order, to the end of the values the built {@link
     * ImmutableDoubleArray} will contain.
     */
    public Builder addAll(ImmutableDoubleArray values) {
      ensureRoomFor(values.length());
      System.arraycopy(values.array, values.start, array, count, values.length());
      count += values.length();
      return this;
    }

    private void ensureRoomFor(int numberToAdd) {
      int newCount = count + numberToAdd; // TODO(kevinb): check overflow now?
      if (newCount > array.length) {
        double[] newArray = new double[expandedCapacity(array.length, newCount)];
        System.arraycopy(array, 0, newArray, 0, count);
        this.array = newArray;
      }
    }

    // Unfortunately this is pasted from ImmutableCollection.Builder.
    private static int expandedCapacity(int oldCapacity, int minCapacity) {
      if (minCapacity < 0) {
        throw new AssertionError("cannot store more than MAX_VALUE elements");
      }
      // careful of overflow!
      int newCapacity = oldCapacity + (oldCapacity >> 1) + 1;
      if (newCapacity < minCapacity) {
        newCapacity = Integer.highestOneBit(minCapacity - 1) << 1;
      }
      if (newCapacity < 0) {
        newCapacity = Integer.MAX_VALUE; // guaranteed to be >= newCapacity
      }
      return newCapacity;
    }

    
Returns a new immutable array. The builder can continue to be used after this call, to append
more values and build again.

Performance note: the returned array is backed by the same array as the builder, so no data is copied as part of this step, but this may occupy more memory than strictly necessary. To copy the data to a right-sized backing array, use .build().trimmed(). 
/**
     * Returns a new immutable array. The builder can continue to be used after this call, to append
     * more values and build again.
     *
     * <p><b>Performance note:</b> the returned array is backed by the same array as the builder, so
     * no data is copied as part of this step, but this may occupy more memory than strictly
     * necessary. To copy the data to a right-sized backing array, use {@code .build().trimmed()}.
     */
    @CheckReturnValue
    public ImmutableDoubleArray build() {
      return count == 0 ? EMPTY : new ImmutableDoubleArray(array, 0, count);
    }
  }

  // Instance stuff here

  // The array is never mutated after storing in this field and the construction strategies ensure
  // it doesn't escape this class
  @SuppressWarnings("Immutable")
  private final double[] array;

  /*
   * TODO(kevinb): evaluate the trade-offs of going bimorphic to save these two fields from most
   * instances. Note that the instances that would get smaller are the right set to care about
   * optimizing, because the rest have the option of calling `trimmed`.
   */

  private final transient int start; // it happens that we only serialize instances where this is 0
  private final int end; // exclusive

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

  private ImmutableDoubleArray(double[] array, int start, int end) {
    this.array = array;
    this.start = start;
    this.end = end;
  }

  
Returns the number of values in this array. 
/** Returns the number of values in this array. */
  public int length() {
    return end - start;
  }

  
Returns true if there are no values in this array (length is zero). 
/** Returns {@code true} if there are no values in this array ({@link #length} is zero). */
  public boolean isEmpty() {
    return end == start;
  }

  
Returns the double value present at the given index. 
Throws:
/**
   * Returns the {@code double} value present at the given index.
   *
   * @throws IndexOutOfBoundsException if {@code index} is negative, or greater than or equal to
   *     {@link #length}
   */
  public double get(int index) {
    Preconditions.checkElementIndex(index, length());
    return array[start + index];
  }

  
Returns the smallest index for which get returns target, or -1 if no such index exists. Values are compared as if by Double.equals. Equivalent to 
asList().indexOf(target). 
/**
   * Returns the smallest index for which {@link #get} returns {@code target}, or {@code -1} if no
   * such index exists. Values are compared as if by {@link Double#equals}. Equivalent to {@code
   * asList().indexOf(target)}.
   */
  public int indexOf(double target) {
    for (int i = start; i < end; i++) {
      if (areEqual(array[i], target)) {
        return i - start;
      }
    }
    return -1;
  }

  
Returns the largest index for which get returns target, or -1 if no such index exists. Values are compared as if by Double.equals. Equivalent to 
asList().lastIndexOf(target). 
/**
   * Returns the largest index for which {@link #get} returns {@code target}, or {@code -1} if no
   * such index exists. Values are compared as if by {@link Double#equals}. Equivalent to {@code
   * asList().lastIndexOf(target)}.
   */
  public int lastIndexOf(double target) {
    for (int i = end - 1; i >= start; i--) {
      if (areEqual(array[i], target)) {
        return i - start;
      }
    }
    return -1;
  }

  
Returns true if target is present at any index in this array. Values are compared as if by Double.equals. Equivalent to asList().contains(target). 
/**
   * Returns {@code true} if {@code target} is present at any index in this array. Values are
   * compared as if by {@link Double#equals}. Equivalent to {@code asList().contains(target)}.
   */
  public boolean contains(double target) {
    return indexOf(target) >= 0;
  }

  
Invokes consumer for each value contained in this array, in order. 
/** Invokes {@code consumer} for each value contained in this array, in order. */
  public void forEach(DoubleConsumer consumer) {
    checkNotNull(consumer);
    for (int i = start; i < end; i++) {
      consumer.accept(array[i]);
    }
  }

  
Returns a stream over the values in this array, in order. 
/** Returns a stream over the values in this array, in order. */
  public DoubleStream stream() {
    return Arrays.stream(array, start, end);
  }

  
Returns a new, mutable copy of this array's values, as a primitive double[]. 
/** Returns a new, mutable copy of this array's values, as a primitive {@code double[]}. */
  public double[] toArray() {
    return Arrays.copyOfRange(array, start, end);
  }

  
Returns a new immutable array containing the values in the specified range.

Performance note: The returned array has the same full memory footprint as this one does (no actual copying is performed). To reduce memory usage, use subArray(start,
end).trimmed(). 
/**
   * Returns a new immutable array containing the values in the specified range.
   *
   * <p><b>Performance note:</b> The returned array has the same full memory footprint as this one
   * does (no actual copying is performed). To reduce memory usage, use {@code subArray(start,
   * end).trimmed()}.
   */
  public ImmutableDoubleArray subArray(int startIndex, int endIndex) {
    Preconditions.checkPositionIndexes(startIndex, endIndex, length());
    return startIndex == endIndex
        ? EMPTY
        : new ImmutableDoubleArray(array, start + startIndex, start + endIndex);
  }

  private Spliterator.OfDouble spliterator() {
    return Spliterators.spliterator(array, start, end, Spliterator.IMMUTABLE | Spliterator.ORDERED);
  }

  
Returns an immutable view of this array's values as a List; note that 
double values are boxed into Double instances on demand, which can be very expensive. The returned list should be used once and discarded. For any usages beyond that, pass the returned list to 
ImmutableList.copyOf and use that list instead. 
/**
   * Returns an immutable <i>view</i> of this array's values as a {@code List}; note that {@code
   * double} values are boxed into {@link Double} instances on demand, which can be very expensive.
   * The returned list should be used once and discarded. For any usages beyond that, pass the
   * returned list to {@link com.google.common.collect.ImmutableList#copyOf(Collection)
   * ImmutableList.copyOf} and use that list instead.
   */
  public List<Double> asList() {
    /*
     * Typically we cache this kind of thing, but much repeated use of this view is a performance
     * anti-pattern anyway. If we cache, then everyone pays a price in memory footprint even if
     * they never use this method.
     */
    return new AsList(this);
  }

  static class AsList extends AbstractList<Double> implements RandomAccess, Serializable {
    private final ImmutableDoubleArray parent;

    private AsList(ImmutableDoubleArray parent) {
      this.parent = parent;
    }

    // inherit: isEmpty, containsAll, toArray x2, iterator, listIterator, stream, forEach, mutations

    @Override
    public int size() {
      return parent.length();
    }

    @Override
    public Double get(int index) {
      return parent.get(index);
    }

    @Override
    public boolean contains(Object target) {
      return indexOf(target) >= 0;
    }

    @Override
    public int indexOf(Object target) {
      return target instanceof Double ? parent.indexOf((Double) target) : -1;
    }

    @Override
    public int lastIndexOf(Object target) {
      return target instanceof Double ? parent.lastIndexOf((Double) target) : -1;
    }

    @Override
    public List<Double> subList(int fromIndex, int toIndex) {
      return parent.subArray(fromIndex, toIndex).asList();
    }

    // The default List spliterator is not efficiently splittable
    @Override
    public Spliterator<Double> spliterator() {
      return parent.spliterator();
    }

    @Override
    public boolean equals(@Nullable Object object) {
      if (object instanceof AsList) {
        AsList that = (AsList) object;
        return this.parent.equals(that.parent);
      }
      // We could delegate to super now but it would still box too much
      if (!(object instanceof List)) {
        return false;
      }
      List<?> that = (List<?>) object;
      if (this.size() != that.size()) {
        return false;
      }
      int i = parent.start;
      // Since `that` is very likely RandomAccess we could avoid allocating this iterator...
      for (Object element : that) {
        if (!(element instanceof Double) || !areEqual(parent.array[i++], (Double) element)) {
          return false;
        }
      }
      return true;
    }

    // Because we happen to use the same formula. If that changes, just don't override this.
    @Override
    public int hashCode() {
      return parent.hashCode();
    }

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

  
Returns true if object is an ImmutableDoubleArray containing the same values as this one, in the same order. Values are compared as if by Double.equals. 
/**
   * Returns {@code true} if {@code object} is an {@code ImmutableDoubleArray} containing the same
   * values as this one, in the same order. Values are compared as if by {@link Double#equals}.
   */
  @Override
  public boolean equals(@Nullable Object object) {
    if (object == this) {
      return true;
    }
    if (!(object instanceof ImmutableDoubleArray)) {
      return false;
    }
    ImmutableDoubleArray that = (ImmutableDoubleArray) object;
    if (this.length() != that.length()) {
      return false;
    }
    for (int i = 0; i < length(); i++) {
      if (!areEqual(this.get(i), that.get(i))) {
        return false;
      }
    }
    return true;
  }

  // Match the behavior of Double.equals()
  private static boolean areEqual(double a, double b) {
    return Double.doubleToLongBits(a) == Double.doubleToLongBits(b);
  }

  
Returns an unspecified hash code for the contents of this immutable array. 
/** Returns an unspecified hash code for the contents of this immutable array. */
  @Override
  public int hashCode() {
    int hash = 1;
    for (int i = start; i < end; i++) {
      hash *= 31;
      hash += Doubles.hashCode(array[i]);
    }
    return hash;
  }

  
Returns a string representation of this array in the same form as Arrays.toString(double[]), for example "[1, 2, 3]". 
/**
   * Returns a string representation of this array in the same form as {@link
   * Arrays#toString(double[])}, for example {@code "[1, 2, 3]"}.
   */
  @Override
  public String toString() {
    if (isEmpty()) {
      return "[]";
    }
    StringBuilder builder = new StringBuilder(length() * 5); // rough estimate is fine
    builder.append('[').append(array[start]);

    for (int i = start + 1; i < end; i++) {
      builder.append(", ").append(array[i]);
    }
    builder.append(']');
    return builder.toString();
  }

  
Returns an immutable array containing the same values as this array. This is logically a no-op, and in some circumstances this itself is returned. However, if this instance is a subArray view of a larger array, this method will copy only the appropriate range of values, resulting in an equivalent array with a smaller memory footprint. 
/**
   * Returns an immutable array containing the same values as {@code this} array. This is logically
   * a no-op, and in some circumstances {@code this} itself is returned. However, if this instance
   * is a {@link #subArray} view of a larger array, this method will copy only the appropriate range
   * of values, resulting in an equivalent array with a smaller memory footprint.
   */
  public ImmutableDoubleArray trimmed() {
    return isPartialView() ? new ImmutableDoubleArray(toArray()) : this;
  }

  private boolean isPartialView() {
    return start > 0 || end < array.length;
  }

  Object writeReplace() {
    return trimmed();
  }

  Object readResolve() {
    return isEmpty() ? EMPTY : this;
  }
}