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Java example source code file (quickSort.hpp)

This example Java source code file (quickSort.hpp) 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

allstatic, product, share_vm_utilities_quicksort_hpp, shouldnotreachhere

The quickSort.hpp Java example source code

/*
 * Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#ifndef SHARE_VM_UTILITIES_QUICKSORT_HPP
#define SHARE_VM_UTILITIES_QUICKSORT_HPP

#include "memory/allocation.hpp"
#include "runtime/globals.hpp"
#include "utilities/debug.hpp"

class QuickSort : AllStatic {

 private:
  template<class T>
  static void swap(T* array, int x, int y) {
    T tmp = array[x];
    array[x] = array[y];
    array[y] = tmp;
  }

  // As pivot we use the median of the first, last and middle elements.
  // We swap in these three values at the right place in the array. This
  // means that this method not only returns the index of the pivot
  // element. It also alters the array so that:
  //     array[first] <= array[middle] <= array[last]
  // A side effect of this is that arrays of length <= 3 are sorted.
  template<class T, class C>
  static int find_pivot(T* array, int length, C comparator) {
    assert(length > 1, "length of array must be > 0");

    int middle_index = length / 2;
    int last_index = length - 1;

    if (comparator(array[0], array[middle_index]) == 1) {
      swap(array, 0, middle_index);
    }
    if (comparator(array[0], array[last_index]) == 1) {
      swap(array, 0, last_index);
    }
    if (comparator(array[middle_index], array[last_index]) == 1) {
      swap(array, middle_index, last_index);
    }
    // Now the value in the middle of the array is the median
    // of the fist, last and middle values. Use this as pivot.
    return middle_index;
  }

  template<class T, class C, bool idempotent>
  static int partition(T* array, int pivot, int length, C comparator) {
    int left_index = -1;
    int right_index = length;
    T pivot_val = array[pivot];

    while (true) {
      do {
        left_index++;
      } while (comparator(array[left_index], pivot_val) == -1);
      do {
        right_index--;
      } while (comparator(array[right_index], pivot_val) == 1);

      if (left_index < right_index) {
        if (!idempotent || comparator(array[left_index], array[right_index]) != 0) {
          swap(array, left_index, right_index);
        }
      } else {
        return right_index;
      }
    }

    ShouldNotReachHere();
    return 0;
  }

  template<class T, class C, bool idempotent>
  static void inner_sort(T* array, int length, C comparator) {
    if (length < 2) {
      return;
    }
    int pivot = find_pivot(array, length, comparator);
    if (length < 4) {
      // arrays up to length 3 will be sorted after finding the pivot
      return;
    }
    int split = partition<T, C, idempotent>(array, pivot, length, comparator);
    int first_part_length = split + 1;
    inner_sort<T, C, idempotent>(array, first_part_length, comparator);
    inner_sort<T, C, idempotent>(&array[first_part_length], length - first_part_length, comparator);
  }

 public:
  // The idempotent parameter prevents the sort from
  // reordering a previous valid sort by not swapping
  // fields that compare as equal. This requires extra
  // calls to the comparator, so the performance
  // impact depends on the comparator.
  template<class T, class C>
  static void sort(T* array, int length, C comparator, bool idempotent) {
    // Switch "idempotent" from function paramter to template parameter
    if (idempotent) {
      inner_sort<T, C, true>(array, length, comparator);
    } else {
      inner_sort<T, C, false>(array, length, comparator);
    }
  }

  // for unit testing
#ifndef PRODUCT
  static void print_array(const char* prefix, int* array, int length);
  static bool compare_arrays(int* actual, int* expected, int length);
  template <class C> static bool sort_and_compare(int* arrayToSort, int* expectedResult, int length, C comparator, bool idempotent = false);
  static void test_quick_sort();
#endif
};


#endif //SHARE_VM_UTILITIES_QUICKSORT_HPP

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