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Java example source code file (Ints.java)

This example Java source code file (Ints.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

annotation, beta, bytes, gwtincompatible, instance, intarrayaslist, intconverter, integer, invalid, number, object, override, serializable, string, stringbuilder, util

The Ints.java Java example source code

/*
 * 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.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 javax.annotation.CheckForNull;
import javax.annotation.Nullable;

/**
 * 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.
 *
 * @author Kevin Bourrillion
 * @since 1.0
 */
@GwtCompatible(emulated = true)
public final class Ints {
  private Ints() {}

  /**
   * The number of bytes required to represent a primitive {@code int} value.
   */
  public static final int BYTES = Integer.SIZE / Byte.SIZE;

  /**
   * 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 {@code value}; equal to the result of invoking
   * {@code ((Integer) value).hashCode()}.
   *
   * @param value a primitive {@code int} value
   * @return a hash code for the value
   */
  public static int hashCode(int value) {
    return 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;
    if (result != value) {
      // don't use checkArgument here, to avoid boxing
      throw new IllegalArgumentException("Out of range: " + value);
    }
    return result;
  }

  /**
   * 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 {@code int} values. The sign of the value returned is the same as
   * that of {@code ((Integer) a).compareTo(b)}.
   *
   * <p>Note for Java 7 and later: 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 {@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 {@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 {@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 {@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 {@code array}.
   *
   * @param array a <i>nonempty 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 {@code array}.
   *
   * @param array a <i>nonempty 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 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 {@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.
   */
  @GwtIncompatible // doesn't work
  public static byte[] toByteArray(int value) {
    return new byte[] {
      (byte) (value >> 24), (byte) (value >> 16), (byte) (value >> 8), (byte) value
    };
  }

  /**
   * 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
   */
  @GwtIncompatible // doesn't work
  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 {@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
   */
  @GwtIncompatible // doesn't work
  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
   * {@link Integer#decode} and {@link Integer#toString()}. The returned converter throws
   * {@link NumberFormatException} if the input string is invalid.
   *
   * <p>Warning: please see {@link Integer#decode} to understand exactly how strings are
   * parsed. For example, the string {@code "0123"} is treated as <i>octal 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 {@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 {@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 {@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()";
    }
  }

  /**
   * 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
   * {@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.
   *
   * @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 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() {
      // Arrays.copyOfRange() is not available under GWT
      int size = size();
      int[] result = new int[size];
      System.arraycopy(array, start, result, 0, size);
      return result;
    }

    private static final long serialVersionUID = 0;
  }

  /**
   * Parses the specified string as a signed decimal integer value. The ASCII character {@code '-'}
   * (<code>'\u002D') 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
  @Nullable
  @CheckForNull
  public static Integer tryParse(String string) {
    return tryParse(string, 10);
  }

  /**
   * Parses the specified string as a signed integer value using the specified radix. The ASCII
   * character {@code '-'} (<code>'\u002D') 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
  @Nullable
  @CheckForNull
  public static 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();
    }
  }
}

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