Collections源码
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Collections类主要是完成了两个主要功能
1.提供了若干简单而又有用的算法，比如排序，二分查找，求最大最小值等等。
2.提供对集合进行包装的静态方法。比如把指定的集合包装成线程安全的集合、包装成不可修改的集合、包装成类型安全的集合等。
package Java.util;
import java.io.Serializable;
import java.io.ObjectOutputStream;
import java.io.IOException;
import java.lang.reflect.Array;
public class Collections {
// Suppresses default constructor, ensuring non-instantiability.
private Collections() {
}
// 算法
/*
*
* 算法需要用到的一些参数。所有的关于List的算法都有两种实现，一种是适合随机访问的 List，另一种是适合连续访问的。
*/
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;
/**
*
* List中的所有元素必须实现Compareable接口,即每个 元素必须是可比的。
*
* 算法的实现原理为： 把指定的List转化为一个对象数组，对数组进行排序，然后迭代List的每一个元素， 在同样的位置重新设置数组中排好序的元素
*/
public static <T extends Comparable<? super T>> void sort(List<T> list) {
Object[] a = list.toArray();
// 转化为对象数组
Arrays.sort(a);
// 对数组排序，使用了归并排序.对此归并的详细分析可见我另一篇博客
ListIterator<T> i = list.listIterator();
for (int j = 0; j < a.length; j++) {
// 迭代元素
i.next();
i.set((T) a[j]);
// 在同样的位置重设排好序的值
}
}
/**
* 传一个实现了Comparator接口的对象进来。 c.compare(o1,o2);来比较两个元素
*/
public static <T> void sort(List<T> list, Comparator<? super T> c) {
Object[] a = list.toArray();
Arrays.sort(a, (Comparator) c);
ListIterator i = list.listIterator();
for (int j = 0; j < a.length; j++) {
i.next();
i.set(a[j]);
}
}
/**
*
* 使用二分查找在指定List中查找指定元素key。 List中的元素必须是有序的。如果List中有多个key，不能确保哪个key值被找到。
* 如果List不是有序的，返回的值没有任何意义
*
* 对于随机访问列表来说，时间复杂度为O(log(n)),比如1024个数只需要查找log2(1024)=10次，
* log2(n)是最坏的情况，即最坏的情况下都只需要找10次
* 对于链表来说，查找中间元素的时间复杂度为O(n),元素比较的时间复杂度为O(log(n))
*
* @return 查找元素的索引。如果返回的是负数表明找不到此元素，但可以用返回值计算
* 应该将key插入到集合什么位置，任然能使集合有序(如果需要插入key值的话)。 公式：point = -i - 1
*
*/
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);
}
/**
* 使用索引化二分查找。 size小于5000的链表也用此方法查找
*/
private static <T> int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key) {
int low = 0; // 元素所在范围的下界
int high = list.size() - 1;
// 上界
while (low <= high) {
int mid = (low + high) >>> 1;
Comparable<? super T> midVal = list.get(mid);
// 中间值
int cmp = midVal.compareTo(key);
// 指定元素与中间值比较
if (cmp < 0)
low = mid + 1;
// 重新设置上界和下界
else if (cmp > 0)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found
}
/**
* 迭代式二分查找，线性查找，依次查找得中间值
*
*/
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);
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(); // 根据当前迭代器的位置确定是向前还是向后遍历找中间值
if (pos <= index) {
do {
obj = i.next();
} while (pos++ < index);
} else {
do {
obj = i.previous();
} while (--pos > index);
}
return obj;
}
/**
* 提供实现了Comparator接口的对象比较元素
*/
public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
if (c == null)
return binarySearch((List) list, key);
if (list instanceof RandomAccess || list.size() < BINARYSEARCH_THRESHOLD)
return Collections.indexedBinarySearch(list, key, c);
else
return Collections.iteratorBinarySearch(list, key, c);
}
private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
int low = 0;
int high = l.size() - 1;
while (low <= high) {
int mid = (low + high) >>> 1;
T midVal = l.get(mid);
int cmp = c.compare(midVal, 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 T> l, T key, Comparator<? super T> c) {
int low = 0;
int high = l.size() - 1;
ListIterator<? extends T> i = l.listIterator();
while (low <= high) {
int mid = (low + high) >>> 1;
T midVal = get(i, mid);
int cmp = c.compare(midVal, 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 interface SelfComparable extends Comparable<SelfComparable> {
}
/**
*
* 逆序排列指定列表中的元素
*/
public static void reverse(List<?> list) {
int size = list.size();
// 如果是size小于18的链表或是基于随机访问的列表
if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) {
for (int i = 0, mid = size >> 1, j = size - 1; i < mid; i++, j--)
// 第一个与最后一个，依次交换
swap(list, i, j); // 交换i和j位置的值
} else { // 基于迭代器的逆序排列算法
ListIterator fwd = list.listIterator();
ListIterator rev = list.listIterator(size);
for (int i = 0, mid = list.size() >> 1; i < mid; i++) {
// 这..，一个思想你懂得
Object tmp = fwd.next();
fwd.set(rev.previous());
rev.set(tmp);
}
}
}
/**
*
* 对指定列表中的元素进行混排
*/
public static void shuffle(List<?> list) {
if (r == null) {
r = new Random();
}
shuffle(list, r);
}
private static Random r;
/**
*
* 提供一个随机数生成器对指定List进行混排
*
* 基本算法思想为： 逆向遍历list，从最后一个元素到第二个元素，然后重复交换当前位置 与随机产生的位置的元素值。
*
* 如果list不是基于随机访问并且其size>5,会先把List中的复制到数组中， 然后对数组进行混排，再把数组中的元素重新填入List中。
* 这样做为了避免迭代器大跨度查找元素影响效率
*/
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--) // 从i-1个位置开始与随机位置元素交换值
swap(list, i - 1, rnd.nextInt(i));
} else {
Object arr[] = list.toArray(); // 先转化为数组
// 对数组进行混排
for (int i = size; i > 1; i--)
swap(arr, i - 1, rnd.nextInt(i));
// 然后把数组中的元素重新填入List
ListIterator it = list.listIterator();
for (int i = 0; i < arr.length; i++) {
it.next();
it.set(arr[i]);
}
}
}
/**
* 交换List中两个位置的值
*/
public static void swap(List<?> list, int i, int j) {
final List l = list;
l.set(i, l.set(j, l.get(i)));
// 互换i和j位置的值
}
/**
* 交换数组俩位置的值。好熟悉啊
*/
private static void swap(Object[] arr, int i, int j) {
Object tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
/**
*
* 用obj替换List中的所有元素 依次遍历赋值即可
*/
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);
}
}
}
/**
*
* 复制源列表的所有元素到目标列表， 如果src.size > dest.size 将抛出一个异常 如果src.size < dest.size
* dest中多出的元素将不受影响 同样是依次遍历赋值
*/
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 { // 一个链表一个线性表也可以用迭代器赋值
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());
}
}
}
/**
*
* 返回集合中的最小元素。前提是其中的元素都是可比的，即实现了Comparable接口 找出一个通用的算法其实不容易，尽管它的思想不难。
* 反正要依次遍历完所有元素，所以直接用了迭代器
*/
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;
}
/**
* 根据提供的比较器求最小元素
*/
public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
if (comp == null)
// 返回默认比较器，其实默认比较器什么也不做，只是看集合元素是否实现了Comparable接口，
// 否则抛出ClassCastException
return (T) min((Collection<SelfComparable>) (Collection) coll);
Iterator<? extends T> i = coll.iterator();
T candidate = i.next();
// 假设第一个元素为最小元素
while (i.hasNext()) {
T next = i.next();
if (comp.compare(next, candidate) < 0)
candidate = next;
}
return candidate;
}
/**
* 求集合中最大元素
*/
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;
}
/**
* 根据指定比较器求集合中最大元素
*/
public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
if (comp == null)
return (T) max((Collection<SelfComparable>) (Collection) coll);
Iterator<? extends T> i = coll.iterator();
T candidate = i.next();
while (i.hasNext()) {
T next = i.next();
if (comp.compare(next, candidate) > 0)
candidate = next;
}
return candidate;
}
/**
*
* 旋转移位List中的元素通过指定的distance。每个元素移动后的位置为： (i +
* distance)%list.size.此方法不会改变列表的长度
*
* 比如，类表元素为： [t, a, n, k, s , w] 执行Collections.rotate(list, 2)或
* Collections.rotate(list, -4)后, list中的元素将变为 [s, w, t, a, n ,
* k]。可以这样理解：正数表示向后移，负数表示向前移
*
*/
public static void rotate(List<?> list, int distance) {
if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)
rotate1((List) list, distance);
else
rotate2((List) list, distance);
}
private static <T> void rotate1(List<T> list, int distance) {
int size = list.size();
if (size == 0)
return;
distance = distance % size; // distance始终处于0到size(不包括)之间
if (distance < 0)
distance += size; // 还是以向后移来计算的
if (distance == 0)
return;
for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
T displaced = list.get(cycleStart);
int i = cycleStart;
do {
i += distance; // 求新位置
if (i >= size)
i -= size; // 超出size就减去size
displaced = list.set(i, displaced);
// 为新位置赋原来的值
nMoved++; // 如果等于size证明全部替换完毕
} while (i != cycleStart); // 依次类推，求新位置的新位置
}
}
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;
// 好神奇啊
reverse(list.subList(0, mid));
reverse(list.subList(mid, size));
reverse(list);
}
/**
*
* 把指定集合中所有与oladVal相等的元素替换成newVal 只要list发生了改变就返回true
*/
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;
}
/**
*
* target是否是source的子集，如果是返回target第一个元素的索引， 否则返回-1。
* 其实这里和串的模式匹配差不多。这里使用的是基本的回溯法。
*
*/
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; // 元素失配，跳到外部循环
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())) {
// 回溯指针，然后跳到外部循环继续执行
for (int j = 0; j < i; j++)
si.previous();
continue nextCand;
}
}
return candidate;
}
}
return -1; // 没有找到匹配的子串返回-1
}
/**
* 如果有一个或多个字串，返回最后一个出现的子串的第一个元素的索引
*/
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)))
// 从source的maxCandidate位置开始比较。然后是maxCandidate-1，依次类推
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
}
// Unmodifiable Wrappers
/**
*
* 返回一个关于指定集合的不可修改的视图。 任何试图修改该视图的操作都将抛出一个UnsupportedOperationException
*
* Collection返回的视图的equals方法不是调用底层集合的equals方法
* 而是继承了Object的equals方法。hashCode方法也是一样的。 因为Set和List的equals方法并不相同。
*/
public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
return new UnmodifiableCollection<T>(c);
}
static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 1820017752578914078L;
final Collection<? extends E> c;
UnmodifiableCollection(Collection<? extends E> c) {
if (c == null)
throw new NullPointerException();
this.c = c;
}
public int size() {
return c.size();
}
public boolean isEmpty() {
return c.isEmpty();
}
public boolean contains(Object o) {
return c.contains(o);
}
public Object[] toArray() {
return c.toArray();
}
public <T> T[] toArray(T[] a) {
return c.toArray(a);
}
public String toString() {
return c.toString();
}
public Iterator<E> iterator() {
return new Iterator<E>() {
Iterator<? extends E> i = c.iterator();
public boolean hasNext() {
return i.hasNext();
}
public E next() {
return i.next();
}
public void remove() {
// 试图修改集合的操作都将抛出此异常
throw new UnsupportedOperationException();
}
};
}
public boolean add(E e) {
throw new UnsupportedOperationException();
}
public boolean remove(Object o) {
throw new UnsupportedOperationException();
}
public boolean containsAll(Collection<?> coll) {
return c.containsAll(coll);
}
public boolean addAll(Collection<? extends E> coll) {
throw new UnsupportedOperationException();
}
public boolean removeAll(Collection<?> coll) {
throw new UnsupportedOperationException();
}
public boolean retainAll(Collection<?> coll) {
throw new UnsupportedOperationException();
}
public void clear() {
throw new UnsupportedOperationException();
}
}
/**
* 返回一个不可修改Set。 调用的是底层集合的equals方法
*/
public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
return new UnmodifiableSet<T>(s);
}
/**
* @serial include
*/
static class UnmodifiableSet<E> extends UnmodifiableCollection<E> implements Set<E>, Serializable {
private static final long serialVersionUID = -9215047833775013803L;
UnmodifiableSet(Set<? extends E> s) {
super(s);
}
public boolean equals(Object o) {
return o == this || c.equals(o);
}
public int hashCode() {
return c.hashCode();
}
}
/**
* 返回一个不可修改的Sort Set
*/
public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
return new UnmodifiableSortedSet<T>(s);
}
static class UnmodifiableSortedSet<E> extends UnmodifiableSet<E> implements SortedSet<E>, Serializable {
private static final long serialVersionUID = -4929149591599911165L;
private final SortedSet<E> ss;
UnmodifiableSortedSet(SortedSet<E> s) {
super(s);
ss = s;
}
public Comparator<? super E> comparator() {
return ss.comparator();
}
public SortedSet<E> subSet(E fromElement, E toElement) {
return new UnmodifiableSortedSet<E>(ss.subSet(fromElement, toElement));
}
public SortedSet<E> headSet(E toElement) {
return new UnmodifiableSortedSet<E>(ss.headSet(toElement));
}
public SortedSet<E> tailSet(E fromElement) {
return new UnmodifiableSortedSet<E>(ss.tailSet(fromElement));
}
public E first() {
return ss.first();
}
public E last() {
return ss.last();
}
}
/**
* 返回一个 不可修改的List 如果原List实现了RandomAccess接口，返回的List也将实现此接口
*/
public static <T> List<T> unmodifiableList(List<? extends T> list) {
return (list instanceof RandomAccess ? new UnmodifiableRandomAccessList<T>(list)
: new UnmodifiableList<T>(list));
}
static class UnmodifiableList<E> extends UnmodifiableCollection<E> implements List<E> {
static final long serialVersionUID = -283967356065247728L;
final List<? extends E> list;
UnmodifiableList(List<? extends E> list) {
super(list);
this.list = list;
}
public boolean equals(Object o) {
return o == this || list.equals(o);
}
public int hashCode() {
return list.hashCode();
}
public E get(int index) {
return list.get(index);
}
public E set(int index, E element) {
throw new UnsupportedOperationException();
}
public void add(int index, E element) {
throw new UnsupportedOperationException();
}
public E remove(int index) {
throw new UnsupportedOperationException();
}
public int indexOf(Object o) {
return list.indexOf(o);
}
public int lastIndexOf(Object o) {
return list.lastIndexOf(o);
}
public boolean addAll(int index, Collection<? extends E> c) {
throw new UnsupportedOperationException();
}
public ListIterator<E> listIterator() {
return listIterator(0);
}
public ListIterator<E> listIterator(final int index) {
return new ListIterator<E>() {
ListIterator<? extends E> i = list.listIterator(index);
public boolean hasNext() {
return i.hasNext();
}
public E next() {
return i.next();
}
public boolean hasPrevious() {
return i.hasPrevious();
}
public E previous() {
return i.previous();
}
public int nextIndex() {
return i.nextIndex();
}
public int previousIndex() {
return i.previousIndex();
}
public void remove() {
throw new UnsupportedOperationException();
}
public void set(E e) {
throw new UnsupportedOperationException();
}
public void add(E e) {
throw new UnsupportedOperationException();
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
return new UnmodifiableList<E>(list.subList(fromIndex, toIndex));
}
/**
* UnmodifiableRandomAccessList instances are serialized as
* UnmodifiableList instances to allow them to be deserialized in
* pre-1.4 JREs (which do not have UnmodifiableRandomAccessList). This
* method inverts the transformation. As a beneficial side-effect, it
* also grafts the RandomAccess marker onto UnmodifiableList instances
* that were serialized in pre-1.4 JREs.
*
* Note: Unfortunately, UnmodifiableRandomAccessList instances
* serialized in 1.4.1 and deserialized in 1.4 will become
* UnmodifiableList instances, as this method was missing in 1.4.
* 这个，自己看吧...
*/
private Object readResolve() {
return (list instanceof RandomAccess ? new UnmodifiableRandomAccessList<E>(list) : this);
}
}
static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E> implements RandomAccess {
UnmodifiableRandomAccessList(List<? extends E> list) {
super(list);
}
public List<E> subList(int fromIndex, int toIndex) {
return new UnmodifiableRandomAccessList<E>(list.subList(fromIndex, toIndex));
}
private static final long serialVersionUID = -2542308836966382001L;
/**
* Allows instances to be deserialized in pre-1.4 JREs (which do not
* have UnmodifiableRandomAccessList). UnmodifiableList has a
* readResolve method that inverts this transformation upon
* deserialization.
*/
private Object writeReplace() {
return new UnmodifiableList<E>(list);
}
}
/**
* 返回一个不可修改的map
*/
public static <K, V> Map<K, V> unmodifiableMap(Map<? extends K, ? extends V> m) {
return new UnmodifiableMap<K, V>(m);
}
private static class UnmodifiableMap<K, V> implements Map<K, V>, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = -1034234728574286014L;
private final Map<? extends K, ? extends V> m;
UnmodifiableMap(Map<? extends K, ? extends V> m) {
if (m == null)
throw new NullPointerException();
this.m = m;
}
public int size() {
return m.size();
}
public boolean isEmpty() {
return m.isEmpty();
}
public boolean containsKey(Object key) {
return m.containsKey(key);
}
public boolean containsValue(Object val) {
return m.containsValue(val);
}
public V get(Object key) {
return m.get(key);
}
public V put(K key, V value) {
throw new UnsupportedOperationException();
}
public V remove(Object key) {
throw new UnsupportedOperationException();
}
public void putAll(Map<? extends K, ? extends V> m) {
throw new UnsupportedOperationException();
}
public void clear() {
throw new UnsupportedOperationException();
}
private transient Set<K> keySet = null;
private transient Set<Map.Entry<K, V>> entrySet = null;
private transient Collection<V> values = null;
// 返回的key集也是不可修改的
public Set<K> keySet() {
if (keySet == null)
keySet = unmodifiableSet(m.keySet());
return keySet;
}
// EntrySet被重新进行包装
public Set<Map.Entry<K, V>> entrySet() {
if (entrySet == null)
entrySet = new UnmodifiableEntrySet<K, V>(m.entrySet());
return entrySet;
}
public Collection<V> values() {
if (values == null)
values = unmodifiableCollection(m.values());
return values;
}
public boolean equals(Object o) {
return o == this || m.equals(o);
}
public int hashCode() {
return m.hashCode();
}
public String toString() {
return m.toString();
}
/**
*
* 需要重新包装返回的EntrySet对象
*/
static class UnmodifiableEntrySet<K, V> extends UnmodifiableSet<Map.Entry<K, V>> {
private static final long serialVersionUID = 7854390611657943733L;
UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
super((Set) s);
}
public Iterator<Map.Entry<K, V>> iterator() {
return new Iterator<Map.Entry<K, V>>() {
// 父类UnmodifiableColletion的c
Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator();
public boolean hasNext() {
return i.hasNext();
}
public Map.Entry<K, V> next() {
return new UnmodifiableEntry<K, V>(i.next());
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public Object[] toArray() {
Object[] a = c.toArray();
for (int i = 0; i < a.length; i++)
a[i] = new UnmodifiableEntry<K, V>((Map.Entry<K, V>) a[i]);
return a;
}
public <T> T[] toArray(T[] a) {
Object[] arr = c.toArray(a.length == 0 ? a : Arrays.copyOf(a, 0));
for (int i = 0; i < arr.length; i++)
arr[i] = new UnmodifiableEntry<K, V>((Map.Entry<K, V>) arr[i]);
if (arr.length > a.length)
return (T[]) arr;
System.arraycopy(arr, 0, a, 0, arr.length);
if (a.length > arr.length)
a[arr.length] = null;
return a;
}
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
return c.contains(new UnmodifiableEntry<K, V>((Map.Entry<K, V>) o));
}
public boolean containsAll(Collection<?> coll) {
Iterator<?> e = coll.iterator();
while (e.hasNext())
if (!contains(e.next())) // Invokes safe contains() above
return false;
return true;
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Set))
return false;
Set s = (Set) o;
if (s.size() != c.size())
return false;
return containsAll(s); // Invokes safe containsAll() above
}
/**
* 重新包装Entry。
*/
private static class UnmodifiableEntry<K, V> implements Map.Entry<K, V> {
private Map.Entry<? extends K, ? extends V> e;
UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {
this.e = e;
}
public K getKey() {
return e.getKey();
}
public V getValue() {
return e.getValue();
}
public V setValue(V value) { // 调用set方法将抛出一个异常
throw new UnsupportedOperationException();
}
public int hashCode() {
return e.hashCode();
}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry t = (Map.Entry) o;
return eq(e.getKey(), t.getKey()) && eq(e.getValue(), t.getValue());
}
public String toString() {
return e.toString();
}
}
}
}
/**
* 返回一个不可修改的SortedMap
*/
public static <K, V> SortedMap<K, V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
return new UnmodifiableSortedMap<K, V>(m);
}
static class UnmodifiableSortedMap<K, V> extends UnmodifiableMap<K, V> implements SortedMap<K, V>, Serializable {
private static final long serialVersionUID = -8806743815996713206L;
private final SortedMap<K, ? extends V> sm;
UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {
super(m);
sm = m;
}
public Comparator<? super K> comparator() {
return sm.comparator();
}
public SortedMap<K, V> subMap(K fromKey, K toKey) {
return new UnmodifiableSortedMap<K, V>(sm.subMap(fromKey, toKey));
}
public SortedMap<K, V> headMap(K toKey) {
return new UnmodifiableSortedMap<K, V>(sm.headMap(toKey));
}
public SortedMap<K, V> tailMap(K fromKey) {
return new UnmodifiableSortedMap<K, V>(sm.tailMap(fromKey));
}
public K firstKey() {
return sm.firstKey();
}
public K lastKey() {
return sm.lastKey();
}
}
// 同步包装
/**
*
* 返回一个线程安全的集合 但是当用户遍历此集合时，需要手动进行同步 Collection c =
* Collections.synchronizedCollection(myCollection); ... synchronized(c) {
* Iterator i = c.iterator(); // Must be in the synchronized block while
* (i.hasNext()) foo(i.next()); }
*
*/
public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
return new SynchronizedCollection<T>(c);
}
static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
return new SynchronizedCollection<T>(c, mutex);
}
/**
* @serial include
*/
static class SynchronizedCollection<E> implements Collection<E>, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 3053995032091335093L;
final Collection<E> c; // 返回的集合
final Object mutex; // 需要同步的对象
SynchronizedCollection(Collection<E> c) {
if (c == null)
throw new NullPointerException();
this.c = c;
mutex = this;
}
SynchronizedCollection(Collection<E> c, Object mutex) {
this.c = c;
this.mutex = mutex;
}
public int size() {
synchronized (mutex) {
return c.size();
}
}
public boolean isEmpty() {
synchronized (mutex) {
return c.isEmpty();
}
}
public boolean contains(Object o) {
synchronized (mutex) {
return c.contains(o);
}
}
public Object[] toArray() {
synchronized (mutex) {
return c.toArray();
}
}
public <T> T[] toArray(T[] a) {
synchronized (mutex) {
return c.toArray(a);
}
}
public Iterator<E> iterator() {
return c.iterator(); // 必须用户自己手动同步
}
public boolean add(E e) {
synchronized (mutex) {
return c.add(e);
}
}
public boolean remove(Object o) {
synchronized (mutex) {
return c.remove(o);
}
}
public boolean containsAll(Collection<?> coll) {
synchronized (mutex) {
return c.containsAll(coll);
}
}
public boolean addAll(Collection<? extends E> coll) {
synchronized (mutex) {
return c.addAll(coll);
}
}
public boolean removeAll(Collection<?> coll) {
synchronized (mutex) {
return c.removeAll(coll);
}
}
public boolean retainAll(Collection<?> coll) {
synchronized (mutex) {
return c.retainAll(coll);
}
}
public void clear() {
synchronized (mutex) {
c.clear();
}
}
public String toString() {
synchronized (mutex) {
return c.toString();
}
}
private void writeObject(ObjectOutputStream s) throws IOException {
synchronized (mutex) {
s.defaultWriteObject();
}
}
}
/**
* 返回一个线程安全的Set
*/
public static <T> Set<T> synchronizedSet(Set<T> s) {
return new SynchronizedSet<T>(s);
}
static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
return new SynchronizedSet<T>(s, mutex);
}
/**
* @serial include
*/
static class SynchronizedSet<E> extends SynchronizedCollection<E> implements Set<E> {
private static final long serialVersionUID = 487447009682186044L;
SynchronizedSet(Set<E> s) {
super(s);
}
SynchronizedSet(Set<E> s, Object mutex) {
super(s, mutex);
}
public boolean equals(Object o) {
synchronized (mutex) {
return c.equals(o);
}
}
public int hashCode() {
synchronized (mutex) {
return c.hashCode();
}
}
}
/**
* 返回一个线程安全的SortedSet
*/
public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
return new SynchronizedSortedSet<T>(s);
}
/**
* @serial include
*/
static class SynchronizedSortedSet<E> extends SynchronizedSet<E> implements SortedSet<E> {
private static final long serialVersionUID = 8695801310862127406L;
final private SortedSet<E> ss;
SynchronizedSortedSet(SortedSet<E> s) {
super(s);
ss = s;
}
SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
super(s, mutex);
ss = s;
}
public Comparator<? super E> comparator() {
synchronized (mutex) {
return ss.comparator();
}
}
public SortedSet<E> subSet(E fromElement, E toElement) {
synchronized (mutex) {
return new SynchronizedSortedSet<E>(ss.subSet(fromElement, toElement), mutex);
}
}
public SortedSet<E> headSet(E toElement) {
synchronized (mutex) {
return new SynchronizedSortedSet<E>(ss.headSet(toElement), mutex);
}
}
public SortedSet<E> tailSet(E fromElement) {
synchronized (mutex) {
return new SynchronizedSortedSet<E>(ss.tailSet(fromElement), mutex);
}
}
public E first() {
synchronized (mutex) {
return ss.first();
}
}
public E last() {
synchronized (mutex) {
return ss.last();
}
}
}
/**
* 返回一个线程安全的List， 如果List是基于随机访问的，返回的List同样实现了RandomAccess接口
*/
public static <T> List<T> synchronizedList(List<T> list) {
return (list instanceof RandomAccess ? new SynchronizedRandomAccessList<T>(list)
: new SynchronizedList<T>(list));
}
static <T> List<T> synchronizedList(List<T> list, Object mutex) {
return (list instanceof RandomAccess ? new SynchronizedRandomAccessList<T>(list, mutex)
: new SynchronizedList<T>(list, mutex));
}
/**
* @serial include
*/
static class SynchronizedList<E> extends SynchronizedCollection<E> implements List<E> {
static final long serialVersionUID = -7754090372962971524L;
final List<E> list;
SynchronizedList(List<E> list) {
super(list);
this.list = list;
}
SynchronizedList(List<E> list, Object mutex) {
super(list, mutex);
this.list = list;
}
public boolean equals(Object o) {
synchronized (mutex) {
return list.equals(o);
}
}
public int hashCode() {
synchronized (mutex) {
return list.hashCode();
}
}
public E get(int index) {
synchronized (mutex) {
return list.get(index);
}
}
public E set(int index, E element) {
synchronized (mutex) {
return list.set(index, element);
}
}
public void add(int index, E element) {
synchronized (mutex) {
list.add(index, element);
}
}
public E remove(int index) {
synchronized (mutex) {
return list.remove(index);
}
}
public int indexOf(Object o) {
synchronized (mutex) {
return list.indexOf(o);
}
}
public int lastIndexOf(Object o) {
synchronized (mutex) {
return list.lastIndexOf(o);
}
}
public boolean addAll(int index, Collection<? extends E> c) {
synchronized (mutex) {
return list.addAll(index, c);
}
}
public ListIterator<E> listIterator() {
return list.listIterator(); // Must be manually synched by user
}
public ListIterator<E> listIterator(int index) {
return list.listIterator(index); // Must be manually synched by user
}
public List<E> subList(int fromIndex, int toIndex) {
synchronized (mutex) {
return new SynchronizedList<E>(list.subList(fromIndex, toIndex), mutex);
}
}
private Object readResolve() {
return (list instanceof RandomAccess ? new SynchronizedRandomAccessList<E>(list) : this);
}
}
/**
* @serial include
*/
static class SynchronizedRandomAccessList<E> extends SynchronizedList<E> implements RandomAccess {
SynchronizedRandomAccessList(List<E> list) {
super(list);
}
SynchronizedRandomAccessList(List<E> list, Object mutex) {
super(list, mutex);
}
public List<E> subList(int fromIndex, int toIndex) {
synchronized (mutex) {
return new SynchronizedRandomAccessList<E>(list.subList(fromIndex, toIndex), mutex);
}
}
static final long serialVersionUID = 1530674583602358482L;
private Object writeReplace() {
return new SynchronizedList<E>(list);
}
}
/**
* 返回一个线程安全的map
*/
public static <K, V> Map<K, V> synchronizedMap(Map<K, V> m) {
return new SynchronizedMap<K, V>(m);
}
/**
* @serial include
*/
private static class SynchronizedMap<K, V> implements Map<K, V>, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 1978198479659022715L;
private final Map<K, V> m; // Backing Map
final Object mutex; // Object on which to synchronize
SynchronizedMap(Map<K, V> m) {
if (m == null)
throw new NullPointerException();
this.m = m;
mutex = this;
}
SynchronizedMap(Map<K, V> m, Object mutex) {
this.m = m;
this.mutex = mutex;
}
public int size() {
synchronized (mutex) {
return m.size();
}
}
public boolean isEmpty() {
synchronized (mutex) {
return m.isEmpty();
}
}
public boolean containsKey(Object key) {
synchronized (mutex) {
return m.containsKey(key);
}
}
public boolean containsValue(Object value) {
synchronized (mutex) {
return m.containsValue(value);
}
}
public V get(Object key) {
synchronized (mutex) {
return m.get(key);
}
}
public V put(K key, V value) {
synchronized (mutex) {
return m.put(key, value);
}
}
public V remove(Object key) {
synchronized (mutex) {
return m.remove(key);
}
}
public void putAll(Map<? extends K, ? extends V> map) {
synchronized (mutex) {
m.putAll(map);
}
}
public void clear() {
synchronized (mutex) {
m.clear();
}
}
private transient Set<K> keySet = null;
private transient Set<Map.Entry<K, V>> entrySet = null;
private transient Collection<V> values = null;
public Set<K> keySet() {
synchronized (mutex) {
if (keySet == null)
keySet = new SynchronizedSet<K>(m.keySet(), mutex);
return keySet;
}
}
public Set<Map.Entry<K, V>> entrySet() {
synchronized (mutex) {
if (entrySet == null)
entrySet = new SynchronizedSet<Map.Entry<K, V>>(m.entrySet(), mutex);
return entrySet;
}
}
public Collection<V> values() {
synchronized (mutex) {
if (values == null)
values = new SynchronizedCollection<V>(m.values(), mutex);
return values;
}
}
public boolean equals(Object o) {
synchronized (mutex) {
return m.equals(o);
}
}
public int hashCode() {
synchronized (mutex) {
return m.hashCode();
}
}
public String toString() {
synchronized (mutex) {
return m.toString();
}
}
private void writeObject(ObjectOutputStream s) throws IOException {
synchronized (mutex) {
s.defaultWriteObject();
}
}
}
/**
* 返回一个线程安全的SortedSet
*/
public static <K, V> SortedMap<K, V> synchronizedSortedMap(SortedMap<K, V> m) {
return new SynchronizedSortedMap<K, V>(m);
}
/**
* @serial include
*/
static class SynchronizedSortedMap<K, V> extends SynchronizedMap<K, V> implements SortedMap<K, V> {
private static final long serialVersionUID = -8798146769416483793L;
private final SortedMap<K, V> sm;
SynchronizedSortedMap(SortedMap<K, V> m) {
super(m);
sm = m;
}
SynchronizedSortedMap(SortedMap<K, V> m, Object mutex) {
super(m, mutex);
sm = m;
}
public Comparator<? super K> comparator() {
synchronized (mutex) {
return sm.comparator();
}
}
public SortedMap<K, V> subMap(K fromKey, K toKey) {
synchronized (mutex) {
return new SynchronizedSortedMap<K, V>(sm.subMap(fromKey, toKey), mutex);
}
}
public SortedMap<K, V> headMap(K toKey) {
synchronized (mutex) {
return new SynchronizedSortedMap<K, V>(sm.headMap(toKey), mutex);
}
}
public SortedMap<K, V> tailMap(K fromKey) {
synchronized (mutex) {
return new SynchronizedSortedMap<K, V>(sm.tailMap(fromKey), mutex);
}
}
public K firstKey() {
synchronized (mutex) {
return sm.firstKey();
}
}
public K lastKey() {
synchronized (mutex) {
return sm.lastKey();
}
}
}
// Dynamically typesafe collection wrappers
/**
*
* 返回一个动态的类型安全的集合。任何试图插入错误类型的元素的操作将立刻抛出 ClassCastException
* 动态类型安全视图的一个主要作用是用作debug调试， 因为它能正确反映出出错的位置。 例如：ArrayList<String> strings =
* new ArrayList<String>(); ArrayList rawList = strings; rawList.add(new
* Date()); add方法并不进行类型检查，所以存入了非String的对象。只有在重新获取该对象 转化为String类型的时候才抛出异常。
* 而动态类型安全的集合能在add时就会抛出ClassCastException。 这种方法的优点是错误可以在正确的位置被报告
*
*
*/
public static <E> Collection<E> checkedCollection(Collection<E> c, Class<E> type) {
return new CheckedCollection<E>(c, type);
}
/**
* @serial include
*/
static class CheckedCollection<E> implements Collection<E>, Serializable {
private static final long serialVersionUID = 1578914078182001775L;
final Collection<E> c;
final Class<E> type;
void typeCheck(Object o) {
if (!type.isInstance(o)) // o是否能被转换成type类型
throw new ClassCastException(
"Attempt to insert " + o.getClass() + " element into collection with element type " + type);
}
CheckedCollection(Collection<E> c, Class<E> type) {
if (c == null || type == null)
throw new NullPointerException();
this.c = c;
this.type = type;
}
public int size() {
return c.size();
}
public boolean isEmpty() {
return c.isEmpty();
}
public boolean contains(Object o) {
return c.contains(o);
}
public Object[] toArray() {
return c.toArray();
}
public <T> T[] toArray(T[] a) {
return c.toArray(a);
}
public String toString() {
return c.toString();
}
public boolean remove(Object o) {
return c.remove(o);
}
public boolean containsAll(Collection<?> coll) {
return c.containsAll(coll);
}
public boolean removeAll(Collection<?> coll) {
return c.removeAll(coll);
}
public boolean retainAll(Collection<?> coll) {
return c.retainAll(coll);
}
public void clear() {
c.clear();
}
public Iterator<E> iterator() {
return new Iterator<E>() {
private final Iterator<E> it = c.iterator();
public boolean hasNext() {
return it.hasNext();
}
public E next() {
return it.next();
}
public void remove() {
it.remove();
}
};
}
public boolean add(E e) {
typeCheck(e); // 添加元素需要进行类型检查
return c.add(e);
}
public boolean addAll(Collection<? extends E> coll) {
E[] a = null;
try {
a = coll.toArray(zeroLengthElementArray());
// 根据zero数组的类型来转换集合为数组。如果coll中含有其他类型这里就会抛出异常
} catch (ArrayStoreException e) {
throw new ClassCastException();
}
boolean result = false;
for (E e : a)
result |= c.add(e); // 只要集合发生了改变就返回true
return result;
}
private E[] zeroLengthElementArray = null; // Lazily initialized
/*
* We don't need locking or volatile, because it's OK if we create
* several zeroLengthElementArrays, and they're immutable.
*/
E[] zeroLengthElementArray() {
if (zeroLengthElementArray == null)
zeroLengthElementArray = (E[]) Array.newInstance(type, 0);
return zeroLengthElementArray;
}
}
/**
* 返回一个会检查类型的集合Set
*/
public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
return new CheckedSet<E>(s, type);
}
/**
* @serial include
*/
static class CheckedSet<E> extends CheckedCollection<E> implements Set<E>, Serializable {
private static final long serialVersionUID = 4694047833775013803L;
CheckedSet(Set<E> s, Class<E> elementType) {
super(s, elementType);
}
public boolean equals(Object o) {
return o == this || c.equals(o);
}
public int hashCode() {
return c.hashCode();
}
}
/**
* 返回一个类型安全的集合SortedSet
*/
public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s, Class<E> type) {
return new CheckedSortedSet<E>(s, type);
}
/**
* @serial include
*/
static class CheckedSortedSet<E> extends CheckedSet<E> implements SortedSet<E>, Serializable {
private static final long serialVersionUID = 1599911165492914959L;
private final SortedSet<E> ss;
CheckedSortedSet(SortedSet<E> s, Class<E> type) {
super(s, type);
ss = s;
}
public Comparator<? super E> comparator() {
return ss.comparator();
}
public E first() {
return ss.first();
}
public E last() {
return ss.last();
}
public SortedSet<E> subSet(E fromElement, E toElement) {
return new CheckedSortedSet<E>(ss.subSet(fromElement, toElement), type);
}
public SortedSet<E> headSet(E toElement) {
return new CheckedSortedSet<E>(ss.headSet(toElement), type);
}
public SortedSet<E> tailSet(E fromElement) {
return new CheckedSortedSet<E>(ss.tailSet(fromElement), type);
}
}
/**
* 返回一个类型安全的集合List
*/
public static <E> List<E> checkedList(List<E> list, Class<E> type) {
return (list instanceof RandomAccess ? new CheckedRandomAccessList<E>(list, type)
: new CheckedList<E>(list, type));
}
/**
* @serial include
*/
static class CheckedList<E> extends CheckedCollection<E> implements List<E> {
static final long serialVersionUID = 65247728283967356L;
final List<E> list;
CheckedList(List<E> list, Class<E> type) {
super(list, type);
this.list = list;
}
public boolean equals(Object o) {
return o == this || list.equals(o);
}
public int hashCode() {
return list.hashCode();
}
public E get(int index) {
return list.get(index);
}
public E remove(int index) {
return list.remove(index);
}
public int indexOf(Object o) {
return list.indexOf(o);
}
public int lastIndexOf(Object o) {
return list.lastIndexOf(o);
}
public E set(int index, E element) {
typeCheck(element);
return list.set(index, element);
}
public void add(int index, E element) {
typeCheck(element);
list.add(index, element);
}
public boolean addAll(int index, Collection<? extends E> c) {
// See CheckCollection.addAll, above, for an explanation
E[] a = null;
try {
a = c.toArray(zeroLengthElementArray());
} catch (ArrayStoreException e) {
throw new ClassCastException();
}
return list.addAll(index, Arrays.asList(a));
}
public ListIterator<E> listIterator() {
return listIterator(0);
}
public ListIterator<E> listIterator(final int index) {
return new ListIterator<E>() {
ListIterator<E> i = list.listIterator(index);
public boolean hasNext() {
return i.hasNext();
}
public E next() {
return i.next();
}
public boolean hasPrevious() {
return i.hasPrevious();
}
public E previous() {
return i.previous();
}
public int nextIndex() {
return i.nextIndex();
}
public int previousIndex() {
return i.previousIndex();
}
public void remove() {
i.remove();
}
public void set(E e) {
typeCheck(e);
i.set(e);
}
public void add(E e) {
typeCheck(e);
i.add(e);
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
return new CheckedList<E>(list.subList(fromIndex, toIndex), type);
}
}
/**
* @serial include
*/
static class CheckedRandomAccessList<E> extends CheckedList<E> implements RandomAccess {
private static final long serialVersionUID = 1638200125423088369L;
CheckedRandomAccessList(List<E> list, Class<E> type) {
super(list, type);
}
public List<E> subList(int fromIndex, int toIndex) {
return new CheckedRandomAccessList<E>(list.subList(fromIndex, toIndex), type);
}
}
/**
* 返回一个类型安全的集合Map
*/
public static <K, V> Map<K, V> checkedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
return new CheckedMap<K, V>(m, keyType, valueType);
}
/**
* @serial include
*/
private static class CheckedMap<K, V> implements Map<K, V>, Serializable {
private static final long serialVersionUID = 5742860141034234728L;
private final Map<K, V> m;
final Class<K> keyType;
final Class<V> valueType;
// 需要对key与value都进行类型检查
private void typeCheck(Object key, Object value) {
if (!keyType.isInstance(key))
throw new ClassCastException(
"Attempt to insert " + key.getClass() + " key into collection with key type " + keyType);
if (!valueType.isInstance(value))
throw new ClassCastException("Attempt to insert " + value.getClass()
+ " value into collection with value type " + valueType);
}
CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
if (m == null || keyType == null || valueType == null)
throw new NullPointerException();
this.m = m;
this.keyType = keyType;
this.valueType = valueType;
}
public int size() {
return m.size();
}
public boolean isEmpty() {
return m.isEmpty();
}
public boolean containsKey(Object key) {
return m.containsKey(key);
}
public boolean containsValue(Object v) {
return m.containsValue(v);
}
public V get(Object key) {
return m.get(key);
}
public V remove(Object key) {
return m.remove(key);
}
public void clear() {
m.clear();
}
public Set<K> keySet() {
return m.keySet();
}
public Collection<V> values() {
return m.values();
}
public boolean equals(Object o) {
return o == this || m.equals(o);
}
public int hashCode() {
return m.hashCode();
}
public String toString() {
return m.toString();
}
public V put(K key, V value) {
typeCheck(key, value);
return m.put(key, value);
}
public void putAll(Map<? extends K, ? extends V> t) {
// See CheckCollection.addAll, above, for an explanation
K[] keys = null;
try {
keys = t.keySet().toArray(zeroLengthKeyArray());
} catch (ArrayStoreException e) {
throw new ClassCastException();
}
V[] values = null;
try {
values = t.values().toArray(zeroLengthValueArray());
} catch (ArrayStoreException e) {
throw new ClassCastException();
}
if (keys.length != values.length)
throw new ConcurrentModificationException();
for (int i = 0; i < keys.length; i++)
m.put(keys[i], values[i]);
}
// Lazily initialized
private K[] zeroLengthKeyArray = null;
private V[] zeroLengthValueArray = null;
/*
* We don't need locking or volatile, because it's OK if we create
* several zeroLengthValueArrays, and they're immutable.
*/
private K[] zeroLengthKeyArray() {
if (zeroLengthKeyArray == null)
zeroLengthKeyArray = (K[]) Array.newInstance(keyType, 0);
return zeroLengthKeyArray;
}
private V[] zeroLengthValueArray() {
if (zeroLengthValueArray == null)
zeroLengthValueArray = (V[]) Array.newInstance(valueType, 0);
return zeroLengthValueArray;
}
private transient Set<Map.Entry<K, V>> entrySet = null;
public Set<Map.Entry<K, V>> entrySet() {
if (entrySet == null)
entrySet = new CheckedEntrySet<K, V>(m.entrySet(), valueType);
return entrySet;
}
/**
* We need this class in addition to CheckedSet as Map.Entry permits
* modification of the backing Map via the setValue operation. This
* class is subtle: there are many possible attacks that must be
* thwarted.
*
* @serial exclude
*/
static class CheckedEntrySet<K, V> implements Set<Map.Entry<K, V>> {
Set<Map.Entry<K, V>> s;
Class<V> valueType;
CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
this.s = s;
this.valueType = valueType;
}
public int size() {
return s.size();
}
public boolean isEmpty() {
return s.isEmpty();
}
public String toString() {
return s.toString();
}
public int hashCode() {
return s.hashCode();
}
public boolean remove(Object o) {
return s.remove(o);
}
public boolean removeAll(Collection<?> coll) {
return s.removeAll(coll);
}
public boolean retainAll(Collection<?> coll) {
return s.retainAll(coll);
}
public void clear() {
s.clear();
}
public boolean add(Map.Entry<K, V> e) {
throw new UnsupportedOperationException();
}
public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
throw new UnsupportedOperationException();
}
public Iterator<Map.Entry<K, V>> iterator() {
return new Iterator<Map.Entry<K, V>>() {
Iterator<Map.Entry<K, V>> i = s.iterator();
public boolean hasNext() {
return i.hasNext();
}
public void remove() {
i.remove();
}
public Map.Entry<K, V> next() {
return new CheckedEntry<K, V>(i.next(), valueType);
}
};
}
public Object[] toArray() {
Object[] source = s.toArray();
/*
* Ensure that we don't get an ArrayStoreException even if
* s.toArray returns an array of something other than Object
*/
Object[] dest = (CheckedEntry.class.isInstance(source.getClass().getComponentType()) ? source
: new Object[source.length]);
for (int i = 0; i < source.length; i++)
dest[i] = new CheckedEntry<K, V>((Map.Entry<K, V>) source[i], valueType);
return dest;
}
public <T> T[] toArray(T[] a) {
// We don't pass a to s.toArray, to avoid window of
// vulnerability wherein an unscrupulous multithreaded client
// could get his hands on raw (unwrapped) Entries from s.
Object[] arr = s.toArray(a.length == 0 ? a : Arrays.copyOf(a, 0));
for (int i = 0; i < arr.length; i++)
arr[i] = new CheckedEntry<K, V>((Map.Entry<K, V>) arr[i], valueType);
if (arr.length > a.length)
return (T[]) arr;
System.arraycopy(arr, 0, a, 0, arr.length);
if (a.length > arr.length)
a[arr.length] = null;
return a;
}
/**
* This method is overridden to protect the backing set against an
* object with a nefarious equals function that senses that the
* equality-candidate is Map.Entry and calls its setValue method.
*/
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
return s.contains(new CheckedEntry<K, V>((Map.Entry<K, V>) o, valueType));
}
/**
* The next two methods are overridden to protect against an
* unscrupulous collection whose contains(Object o) method senses
* when o is a Map.Entry, and calls o.setValue.
*/
public boolean containsAll(Collection<?> coll) {
Iterator<?> e = coll.iterator();
while (e.hasNext())
if (!contains(e.next())) // Invokes safe contains() above
return false;
return true;
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Set))
return false;
Set<?> that = (Set<?>) o;
if (that.size() != s.size())
return false;
return containsAll(that); // Invokes safe containsAll() above
}
/**
* This "wrapper class" serves two purposes: it prevents the client
* from modifying the backing Map, by short-circuiting the setValue
* method, and it protects the backing Map against an ill-behaved
* Map.Entry that attempts to modify another Map Entry when asked to
* perform an equality check.
*/
private static class CheckedEntry<K, V> implements Map.Entry<K, V> {
private Map.Entry<K, V> e;
private Class<V> valueType;
CheckedEntry(Map.Entry<K, V> e, Class<V> valueType) {
this.e = e;
this.valueType = valueType;
}
public K getKey() {
return e.getKey();
}
public V getValue() {
return e.getValue();
}
public int hashCode() {
return e.hashCode();
}
public String toString() {
return e.toString();
}
public V setValue(V value) {
if (!valueType.isInstance(value))
throw new ClassCastException("Attempt to insert " + value.getClass()
+ " value into collection with value type " + valueType);
return e.setValue(value);
}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry t = (Map.Entry) o;
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