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 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 int primitives, that are not already found in either Integer or Arrays. 
See the Guava User Guide article on primitive utilities.

Author:Kevin Bourrillion
Since:1.0
/**
 * Static utility methods pertaining to {@code int} primitives, that are not already found in either
 * {@link Integer} 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 Ints {
  private Ints() {}

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

  
The largest power of two that can be represented as an int. 
Since:10.0
/**
   * The largest power of two that can be represented as an {@code int}.
   *
   * @since 10.0
   */
  public static final int MAX_POWER_OF_TWO = 1 << (Integer.SIZE - 2);

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

  
Returns the int value that is equal to value, if possible. 
Params:
  • value – any value in the range of the int type
Throws:
Returns:the int value that equals value
/**
   * Returns the {@code int} value that is equal to {@code value}, if possible.
   *
   * @param value any value in the range of the {@code int} type
   * @return the {@code int} value that equals {@code value}
   * @throws IllegalArgumentException if {@code value} is greater than {@link Integer#MAX_VALUE} or
   *     less than {@link Integer#MIN_VALUE}
   */
  public static int checkedCast(long value) {
    int result = (int) value;
    checkArgument(result == value, "Out of range: %s", value);
    return result;
  }

  
Returns the int nearest in value to value. 
Params:
  • value – any long value
Returns:the same value cast to int if it is in the range of the int type, Integer.MAX_VALUE if it is too large, or Integer.MIN_VALUE if it is too small
/**
   * Returns the {@code int} nearest in value to {@code value}.
   *
   * @param value any {@code long} value
   * @return the same value cast to {@code int} if it is in the range of the {@code int} type,
   *     {@link Integer#MAX_VALUE} if it is too large, or {@link Integer#MIN_VALUE} if it is too
   *     small
   */
  public static int saturatedCast(long value) {
    if (value > Integer.MAX_VALUE) {
      return Integer.MAX_VALUE;
    }
    if (value < Integer.MIN_VALUE) {
      return Integer.MIN_VALUE;
    }
    return (int) value;
  }

  
Compares the two specified int values. The sign of the value returned is the same as that of ((Integer) a).compareTo(b). 
Note for Java 7 and later: this method should be treated as deprecated; use the equivalent Integer.compare method instead. 
Params:
  • a – the first int to compare
  • b – the second int 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 int} values. The sign of the value returned is the same as
   * that of {@code ((Integer) a).compareTo(b)}.
   *
   * <p><b>Note for Java 7 and later:</b> this method should be treated as deprecated; use the
   * equivalent {@link Integer#compare} method instead.
   *
   * @param a the first {@code int} to compare
   * @param b the second {@code int} 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(int a, int b) {
    return (a < b) ? -1 : ((a > b) ? 1 : 0);
  }

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

  
Returns the index of the first appearance of the value target in array. 
Params:
  • array – an array of int values, possibly empty
  • target – a primitive int 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}.
   *
   * @param array an array of {@code int} values, possibly empty
   * @param target a primitive {@code int} 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(int[] array, int target) {
    return indexOf(array, target, 0, array.length);
  }

  // TODO(kevinb): consider making this public
  private static int indexOf(int[] array, int 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(int[] array, int[] 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 int values, possibly empty
  • target – a primitive int 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 int} values, possibly empty
   * @param target a primitive {@code int} 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(int[] array, int target) {
    return lastIndexOf(array, target, 0, array.length);
  }

  // TODO(kevinb): consider making this public
  private static int lastIndexOf(int[] array, int 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. 
Params:
  • array – a nonempty array of int 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}.
   *
   * @param array a <i>nonempty</i> array of {@code int} 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 int min(int... array) {
    checkArgument(array.length > 0);
    int min = array[0];
    for (int i = 1; i < array.length; i++) {
      if (array[i] < min) {
        min = array[i];
      }
    }
    return min;
  }

  
Returns the greatest value present in array. 
Params:
  • array – a nonempty array of int 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}.
   *
   * @param array a <i>nonempty</i> array of {@code int} 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 int max(int... array) {
    checkArgument(array.length > 0);
    int max = array[0];
    for (int i = 1; i < array.length; i++) {
      if (array[i] > 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 int 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 int} 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 int constrainToRange(int value, int min, int 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 int[] {a, b}, new int[] {}, new int[] {c} returns the array {a, b, c}. 
Params:
  • arrays – zero or more int 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 int[] {a, b}, new int[] {}, new int[] {c}} returns the array {@code {a, b, c}}.
   *
   * @param arrays zero or more {@code int} arrays
   * @return a single array containing all the values from the source arrays, in order
   */
  public static int[] concat(int[]... arrays) {
    int length = 0;
    for (int[] array : arrays) {
      length += array.length;
    }
    int[] result = new int[length];
    int pos = 0;
    for (int[] array : arrays) {
      System.arraycopy(array, 0, result, pos, array.length);
      pos += array.length;
    }
    return result;
  }

  
Returns a big-endian representation of value in a 4-element byte array; equivalent to ByteBuffer.allocate(4).putInt(value).array(). For example, the input value 
0x12131415 would yield the byte array {0x12, 0x13, 0x14, 0x15}. 
If you need to convert and concatenate several values (possibly even of different types), use a shared ByteBuffer instance, or use ByteStreams.newDataOutput() to get a growable buffer. 
/**
   * Returns a big-endian representation of {@code value} in a 4-element byte array; equivalent to
   * {@code ByteBuffer.allocate(4).putInt(value).array()}. For example, the input value {@code
   * 0x12131415} would yield the byte array {@code {0x12, 0x13, 0x14, 0x15}}.
   *
   * <p>If you need to convert and concatenate several values (possibly even of different types),
   * use a shared {@link java.nio.ByteBuffer} instance, or use {@link
   * com.google.common.io.ByteStreams#newDataOutput()} to get a growable buffer.
   */
  public static byte[] toByteArray(int value) {
    return new byte[] {
      (byte) (value >> 24), (byte) (value >> 16), (byte) (value >> 8), (byte) value
    };
  }

  
Returns the int value whose big-endian representation is stored in the first 4 bytes of bytes; equivalent to ByteBuffer.wrap(bytes).getInt(). For example, the input byte array {0x12, 0x13, 0x14, 0x15, 0x33} would yield the int value 
0x12131415. 
Arguably, it's preferable to use ByteBuffer; that library exposes much more flexibility at little cost in readability. 
Throws:
/**
   * Returns the {@code int} value whose big-endian representation is stored in the first 4 bytes of
   * {@code bytes}; equivalent to {@code ByteBuffer.wrap(bytes).getInt()}. For example, the input
   * byte array {@code {0x12, 0x13, 0x14, 0x15, 0x33}} would yield the {@code int} value {@code
   * 0x12131415}.
   *
   * <p>Arguably, it's preferable to use {@link java.nio.ByteBuffer}; that library exposes much more
   * flexibility at little cost in readability.
   *
   * @throws IllegalArgumentException if {@code bytes} has fewer than 4 elements
   */
  public static int fromByteArray(byte[] bytes) {
    checkArgument(bytes.length >= BYTES, "array too small: %s < %s", bytes.length, BYTES);
    return fromBytes(bytes[0], bytes[1], bytes[2], bytes[3]);
  }

  
Returns the int value whose byte representation is the given 4 bytes, in big-endian order; equivalent to Ints.fromByteArray(new byte[] {b1, b2, b3, b4}). 
Since:7.0
/**
   * Returns the {@code int} value whose byte representation is the given 4 bytes, in big-endian
   * order; equivalent to {@code Ints.fromByteArray(new byte[] {b1, b2, b3, b4})}.
   *
   * @since 7.0
   */
  public static int fromBytes(byte b1, byte b2, byte b3, byte b4) {
    return b1 << 24 | (b2 & 0xFF) << 16 | (b3 & 0xFF) << 8 | (b4 & 0xFF);
  }

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

    @Override
    protected Integer doForward(String value) {
      return Integer.decode(value);
    }

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

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

    private Object readResolve() {
      return INSTANCE;
    }

    private static final long serialVersionUID = 1;
  }

  
Returns a serializable converter object that converts between strings and integers using Integer.decode and Integer.toString(). The returned converter throws NumberFormatException if the input string is invalid. 
Warning: please see Integer.decode to understand exactly how strings are parsed. For example, the string "0123" is treated as octal and converted to the value 83. 
Since:16.0
/**
   * Returns a serializable converter object that converts between strings and integers using {@link
   * Integer#decode} and {@link Integer#toString()}. The returned converter throws {@link
   * NumberFormatException} if the input string is invalid.
   *
   * <p><b>Warning:</b> please see {@link Integer#decode} to understand exactly how strings are
   * parsed. For example, the string {@code "0123"} is treated as <i>octal</i> and converted to the
   * value {@code 83}.
   *
   * @since 16.0
   */
  @Beta
  public static Converter<String, Integer> stringConverter() {
    return IntConverter.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 int[] ensureCapacity(int[] 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 int values separated by separator. For example, join("-", 1, 2, 3) 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 int values, possibly empty
/**
   * Returns a string containing the supplied {@code int} values separated by {@code separator}. For
   * example, {@code join("-", 1, 2, 3)} 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 int} values, possibly empty
   */
  public static String join(String separator, int... 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 * 5);
    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 int arrays lexicographically. That is, it compares, using compare(int, int)), 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] < [1, 2] < [2]. 
The returned comparator is inconsistent with Object.equals(Object) (since arrays support only identity equality), but it is consistent with Arrays.equals(int[], int[]). 
Since:2.0
/**
   * Returns a comparator that compares two {@code int} arrays <a
   * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>. That is, it
   * compares, using {@link #compare(int, int)}), 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] < [1, 2] < [2]}.
   *
   * <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(int[], int[])}.
   *
   * @since 2.0
   */
  public static Comparator<int[]> lexicographicalComparator() {
    return LexicographicalComparator.INSTANCE;
  }

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

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

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

  
Sorts the elements of array in descending order. 
Since:23.1
/**
   * Sorts the elements of {@code array} in descending order.
   *
   * @since 23.1
   */
  public static void sortDescending(int[] array) {
    checkNotNull(array);
    sortDescending(array, 0, array.length);
  }

  
Sorts the elements of array between fromIndex inclusive and toIndex exclusive in descending order. 
Since:23.1
/**
   * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
   * exclusive in descending order.
   *
   * @since 23.1
   */
  public static void sortDescending(int[] 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(Ints.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(Ints.asList(array))}, but is likely to be more efficient.
   *
   * @since 23.1
   */
  public static void reverse(int[] 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(Ints.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(Ints.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(int[] array, int fromIndex, int toIndex) {
    checkNotNull(array);
    checkPositionIndexes(fromIndex, toIndex, array.length);
    for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
      int tmp = array[i];
      array[i] = array[j];
      array[j] = tmp;
    }
  }

  
Returns an array containing each value of collection, converted to a int value in the manner of Number.intValue. 
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<Integer> before 12.0)
/**
   * Returns an array containing each value of {@code collection}, converted to a {@code int} value
   * in the manner of {@link Number#intValue}.
   *
   * <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<Integer>} before 12.0)
   */
  public static int[] toArray(Collection<? extends Number> collection) {
    if (collection instanceof IntArrayAsList) {
      return ((IntArrayAsList) collection).toIntArray();
    }

    Object[] boxedArray = collection.toArray();
    int len = boxedArray.length;
    int[] array = new int[len];
    for (int i = 0; i < len; i++) {
      // checkNotNull for GWT (do not optimize)
      array[i] = ((Number) checkNotNull(boxedArray[i])).intValue();
    }
    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 Integer objects written to or read from it. For example, whether list.get(0) == list.get(0) is true for the returned list is unspecified. 
Note: when possible, you should represent your data as an ImmutableIntArray 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 Integer} 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><b>Note:</b> when possible, you should represent your data as an {@link ImmutableIntArray}
   * instead, which has an {@link ImmutableIntArray#asList asList} view.
   *
   * @param backingArray the array to back the list
   * @return a list view of the array
   */
  public static List<Integer> asList(int... backingArray) {
    if (backingArray.length == 0) {
      return Collections.emptyList();
    }
    return new IntArrayAsList(backingArray);
  }

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

    IntArrayAsList(int[] array) {
      this(array, 0, array.length);
    }

    IntArrayAsList(int[] 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 Integer get(int index) {
      checkElementIndex(index, size());
      return array[start + index];
    }

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

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

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

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

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

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

    @Override
    public String toString() {
      StringBuilder builder = new StringBuilder(size() * 5);
      builder.append('[').append(array[start]);
      for (int i = start + 1; i < end; i++) {
        builder.append(", ").append(array[i]);
      }
      return builder.append(']').toString();
    }

    int[] toIntArray() {
      return Arrays.copyOfRange(array, start, end);
    }

    private static final long serialVersionUID = 0;
  }

  
Parses the specified string as a signed decimal integer value. The ASCII character '-' ('\u002D') is recognized as the minus sign.

Unlike Integer.parseInt(String), this method returns null instead of throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits, and returns null if non-ASCII digits are present in the string. 
Note that strings prefixed with ASCII '+' are rejected, even under JDK 7, despite the change to Integer.parseInt(String) for that version. 
Params:
  • string – the string representation of an integer value
Returns:the integer value represented by string, or null if string has a length of zero or cannot be parsed as an integer value
Since:11.0
/**
   * Parses the specified string as a signed decimal integer value. The ASCII character {@code '-'}
   * (<code>'&#92;u002D'</code>) is recognized as the minus sign.
   *
   * <p>Unlike {@link Integer#parseInt(String)}, this method returns {@code null} instead of
   * throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits,
   * and returns {@code null} if non-ASCII digits are present in the string.
   *
   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even under JDK 7, despite
   * the change to {@link Integer#parseInt(String)} for that version.
   *
   * @param string the string representation of an integer value
   * @return the integer value represented by {@code string}, or {@code null} if {@code string} has
   *     a length of zero or cannot be parsed as an integer value
   * @since 11.0
   */
  @Beta
  public static @Nullable Integer tryParse(String string) {
    return tryParse(string, 10);
  }

  
Parses the specified string as a signed integer value using the specified radix. The ASCII character '-' ('\u002D') is recognized as the minus sign.

Unlike Integer.parseInt(String, int), this method returns null instead of throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits, and returns null if non-ASCII digits are present in the string. 
Note that strings prefixed with ASCII '+' are rejected, even under JDK 7, despite the change to Integer.parseInt(String, int) for that version. 
Params:
  • string – the string representation of an integer value
  • radix – the radix to use when parsing
Throws:
Returns:the integer value represented by string using radix, or null if string has a length of zero or cannot be parsed as an integer value
Since:19.0
/**
   * Parses the specified string as a signed integer value using the specified radix. The ASCII
   * character {@code '-'} (<code>'&#92;u002D'</code>) is recognized as the minus sign.
   *
   * <p>Unlike {@link Integer#parseInt(String, int)}, this method returns {@code null} instead of
   * throwing an exception if parsing fails. Additionally, this method only accepts ASCII digits,
   * and returns {@code null} if non-ASCII digits are present in the string.
   *
   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even under JDK 7, despite
   * the change to {@link Integer#parseInt(String, int)} for that version.
   *
   * @param string the string representation of an integer value
   * @param radix the radix to use when parsing
   * @return the integer value represented by {@code string} using {@code radix}, or {@code null} if
   *     {@code string} has a length of zero or cannot be parsed as an integer value
   * @throws IllegalArgumentException if {@code radix < Character.MIN_RADIX} or {@code radix >
   *     Character.MAX_RADIX}
   * @since 19.0
   */
  @Beta
  public static @Nullable Integer tryParse(String string, int radix) {
    Long result = Longs.tryParse(string, radix);
    if (result == null || result.longValue() != result.intValue()) {
      return null;
    } else {
      return result.intValue();
    }
  }
}