Java 集合类 Collections源码分析

package java.util;
import java.io.Serializable;
import java.io.ObjectOutputStream;
import java.io.IOException;
import java.lang.reflect.Array;



public class Collections {
    private Collections() {/**这是一个工具类,私有化构造方法**/
    }
  /**一系列对外不可见的静态常量,规定了二分查找、逆序、混排、填充、旋转、拷贝、替换、求下标的一些列阈值;**/
    private static final int BINARYSEARCH_THRESHOLD   = 5000;
    private static final int REVERSE_THRESHOLD        =   18;
    private static final int SHUFFLE_THRESHOLD        =    5;
    private static final int FILL_THRESHOLD           =   25;
    private static final int ROTATE_THRESHOLD         =  100;
    private static final int COPY_THRESHOLD           =   10;
    private static final int REPLACEALL_THRESHOLD     =   11;
    private static final int INDEXOFSUBLIST_THRESHOLD =   35;

    /**sort()方法调用的就是Arrays.sort();**/
    public static <T extends Comparable<? super T>> void sort(List<T> list) {
        Object[] a = list.toArray();
        Arrays.sort(a);
        ListIterator<T> i = list.listIterator();
        for (int j=0; j<a.length; j++) {
            i.next();
            i.set((T)a[j]);
        }
    }
/**带有比较器的sort();**/
     public static <T> void sort(List<T> list, Comparator<? super T> c) {  }//具体代码省略
 /**下面几个方法是二分查找，分为iteratorBinarySearch和indexedBinarySearch;比较两个查找的唯一区别就是get元素不同*/
    public static <T>
    int binarySearch(List<? extends Comparable<? super T>> list, T key) {
        if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
            return Collections.indexedBinarySearch(list, key);
        else
            return Collections.iteratorBinarySearch(list, key);
    }

    private static <T>
    int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key)
    {
        int low = 0;
        int high = list.size()-1;

        while (low <= high) {
            int mid = (low + high) >>> 1;
            Comparable<? super T> midVal = list.get(mid);/**直接list.get()顺序存储的优势**/
            int cmp = midVal.compareTo(key);

            if (cmp < 0)
                low = mid + 1;
            else if (cmp > 0)
                high = mid - 1;
            else
                return mid; // key found
        }
        return -(low + 1);  // key not found
    }

    private static <T>
    int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key)
    {
        int low = 0;
        int high = list.size()-1;
        ListIterator<? extends Comparable<? super T>> i = list.listIterator();

        while (low <= high) {
            int mid = (low + high) >>> 1;
            Comparable<? super T> midVal = get(i, mid);/**链式存储的话要单独的get()方法遍历**/
            int cmp = midVal.compareTo(key);

            if (cmp < 0)
                low = mid + 1;
            else if (cmp > 0)
                high = mid - 1;
            else
                return mid; // key found
        }
        return -(low + 1);  // key not found
    }

    
    private static <T> T get(ListIterator<? extends T> i, int index) {
        T obj = null;
        int pos = i.nextIndex();
        if (pos <= index) {
            do {
                obj = i.next();
            } while (pos++ < index);
        } else {
            do {
                obj = i.previous();
            } while (--pos > index);
        }
        return obj;
    }

   /**带有比较器的二分查找具体代码忽略本质上一样**/
    public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
    }

    private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
    }

    private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
    }

    private interface SelfComparable extends Comparable<SelfComparable> {}


  /**逆转数组**/
    public static void reverse(List<?> list) {
        int size = list.size();
        if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) {
            for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--)
                swap(list, i, j);
        } else {
            ListIterator fwd = list.listIterator();
            ListIterator rev = list.listIterator(size);
            for (int i=0, mid=list.size()>>1; i<mid; i++) {
                Object tmp = fwd.next();
                fwd.set(rev.previous());
                rev.set(tmp);
            }
        }
    }

    /**混排数组**/
    public static void shuffle(List<?> list) {
        Random rnd = r;
        if (rnd == null)
            r = rnd = new Random();
        shuffle(list, rnd);
    }
    private static Random r;
    /***混排数组，每次生成一个随机数,交换arr[r]和arr[i-1]**/
    public static void shuffle(List<?> list, Random rnd) {
        int size = list.size();
        if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
            for (int i=size; i>1; i--)
                swap(list, i-1, rnd.nextInt(i));
        } else {
            Object arr[] = list.toArray();

            // Shuffle array
            for (int i=size; i>1; i--)
                swap(arr, i-1, rnd.nextInt(i));

            // Dump array back into list
            ListIterator it = list.listIterator();
            for (int i=0; i<arr.length; i++) {
                it.next();
                it.set(arr[i]);
            }
        }
    }

    public static void swap(List<?> list, int i, int j) {
        final List l = list;
        l.set(i, l.set(j, l.get(i)));
    }

    private static void swap(Object[] arr, int i, int j) {
        Object tmp = arr[i];
        arr[i] = arr[j];
        arr[j] = tmp;
    }

 /**填充值**/
    public static <T> void fill(List<? super T> list, T obj) {
        int size = list.size();

        if (size < FILL_THRESHOLD || list instanceof RandomAccess) {
            for (int i=0; i<size; i++)
                list.set(i, obj);
        } else {
            ListIterator<? super T> itr = list.listIterator();
            for (int i=0; i<size; i++) {
                itr.next();
                itr.set(obj);
            }
        }
    }

   /**拷贝值**/
    public static <T> void copy(List<? super T> dest, List<? extends T> src) {
        int srcSize = src.size();
        if (srcSize > dest.size())
            throw new IndexOutOfBoundsException("Source does not fit in dest");

        if (srcSize < COPY_THRESHOLD ||
            (src instanceof RandomAccess && dest instanceof RandomAccess)) {
            for (int i=0; i<srcSize; i++)
                dest.set(i, src.get(i));
        } else {
            ListIterator<? super T> di=dest.listIterator();
            ListIterator<? extends T> si=src.listIterator();
            for (int i=0; i<srcSize; i++) {
                di.next();
                di.set(si.next());
            }
        }
    }

 /**求最小值**/
    public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {
        Iterator<? extends T> i = coll.iterator();
        T candidate = i.next();

        while (i.hasNext()) {
            T next = i.next();
            if (next.compareTo(candidate) < 0)
                candidate = next;
        }
        return candidate;
    }

   /**带有比较器的最小值**/
    public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
       
    }

   /**最大值**/
    public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
        Iterator<? extends T> i = coll.iterator();
        T candidate = i.next();

        while (i.hasNext()) {
            T next = i.next();
            if (next.compareTo(candidate) > 0)
                candidate = next;
        }
        return candidate;
    }

  /**带有比较器的最大值**/
    public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
       
    }

   /**旋转，分为顺序随机存储的旋转和链式存储的旋转**/
    public static void rotate(List<?> list, int distance) {
        if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)
            rotate1(list, distance);
        else
            rotate2(list, distance);
    }

    private static <T> void rotate1(List<T> list, int distance) {
        int size = list.size();
        if (size == 0)
            return;
        distance = distance % size;
        if (distance < 0)
            distance += size;
        if (distance == 0)
            return;

        for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
            T displaced = list.get(cycleStart);
            int i = cycleStart;
            do {
                i += distance;
                if (i >= size)
                    i -= size;
                displaced = list.set(i, displaced);
                nMoved ++;
            } while (i != cycleStart);
        }
    }

    private static void rotate2(List<?> list, int distance) {
        int size = list.size();
        if (size == 0)
            return;
        int mid =  -distance % size;
        if (mid < 0)
            mid += size;
        if (mid == 0)
            return;

        reverse(list.subList(0, mid));
        reverse(list.subList(mid, size));
        reverse(list);
    }

    /**替换*/
    public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {
        boolean result = false;
        int size = list.size();
        if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) {
            if (oldVal==null) {
                for (int i=0; i<size; i++) {
                    if (list.get(i)==null) {
                        list.set(i, newVal);
                        result = true;
                    }
                }
            } else {
                for (int i=0; i<size; i++) {
                    if (oldVal.equals(list.get(i))) {
                        list.set(i, newVal);
                        result = true;
                    }
                }
            }
        } else {
            ListIterator<T> itr=list.listIterator();
            if (oldVal==null) {
                for (int i=0; i<size; i++) {
                    if (itr.next()==null) {
                        itr.set(newVal);
                        result = true;
                    }
                }
            } else {
                for (int i=0; i<size; i++) {
                    if (oldVal.equals(itr.next())) {
                        itr.set(newVal);
                        result = true;
                    }
                }
            }
        }
        return result;
    }

    /**求子集*/
    public static int indexOfSubList(List<?> source, List<?> target) {
        int sourceSize = source.size();
        int targetSize = target.size();
        int maxCandidate = sourceSize - targetSize;

        if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
            (source instanceof RandomAccess&&target instanceof RandomAccess)) {
        nextCand:
            for (int candidate = 0; candidate <= maxCandidate; candidate++) {
                for (int i=0, j=candidate; i<targetSize; i++, j++)
                    if (!eq(target.get(i), source.get(j)))
                        continue nextCand;  // Element mismatch, try next cand
                return candidate;  // All elements of candidate matched target
            }
        } else {  // Iterator version of above algorithm
            ListIterator<?> si = source.listIterator();
        nextCand:
            for (int candidate = 0; candidate <= maxCandidate; candidate++) {
                ListIterator<?> ti = target.listIterator();
                for (int i=0; i<targetSize; i++) {
                    if (!eq(ti.next(), si.next())) {
                        // Back up source iterator to next candidate
                        for (int j=0; j<i; j++)
                            si.previous();
                        continue nextCand;
                    }
                }
                return candidate;
            }
        }
        return -1;  // No candidate matched the target
    }

    /**依然求子集，但是是从后面往前数*/
    public static int lastIndexOfSubList(List<?> source, List<?> target) {
        int sourceSize = source.size();
        int targetSize = target.size();
        int maxCandidate = sourceSize - targetSize;

        if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
            source instanceof RandomAccess) {   // Index access version
        nextCand:
            for (int candidate = maxCandidate; candidate >= 0; candidate--) {
                for (int i=0, j=candidate; i<targetSize; i++, j++)
                    if (!eq(target.get(i), source.get(j)))
                        continue nextCand;  // Element mismatch, try next cand
                return candidate;  // All elements of candidate matched target
            }
        } else {  // Iterator version of above algorithm
            if (maxCandidate < 0)
                return -1;
            ListIterator<?> si = source.listIterator(maxCandidate);
        nextCand:
            for (int candidate = maxCandidate; candidate >= 0; candidate--) {
                ListIterator<?> ti = target.listIterator();
                for (int i=0; i<targetSize; i++) {
                    if (!eq(ti.next(), si.next())) {
                        if (candidate != 0) {
                            // Back up source iterator to next candidate
                            for (int j=0; j<=i+1; j++)
                                si.previous();
                        }
                        continue nextCand;
                    }
                }
                return candidate;
            }
        }
        return -1;  // No candidate matched the target
    }
/**后面是大量的内部类直接忽略**/
}