我正在尝试在 java 中存储唯一整数数组的列表。我无法使用哈希集，因为 .equals 方法不会将具有相同值但不同引用的 int[] 等同。
3 回答
跃然一笑
TA贡献1826条经验 获得超6个赞
一种选择是使用List<Integer>而不是int[]作为 的元素Set，这将允许您使用任何Set实现。
如果必须使用数组，可以将它们存储在 a 中TreeSet<int[]>，并将自定义Comparator<int[]>传递给TreeSet构造函数。这应该可行，因为TreeSet不使用equals()andhashCode()来确定两个元素是否相同。
摇曳的蔷薇
TA贡献1793条经验 获得超6个赞
我认为以下代码片段将是您的解决方案。如果我答对了
List<Integer> numberList = new ArrayList<Integer>();
int[] myInts = {1, 1, 2, 3, 3, 3, 3, 4};
for (int i : myInts) {
if (!numberList.contains(i)) {
numberList.add(i);
}
}
一只斗牛犬
TA贡献1784条经验 获得超2个赞
您可以将int[]数组包装在一个特殊的容器中，该容器会覆盖equals和hashCode：
public class IntArrayHolder {
private final int[] array;
public IntArrayHolder(int[] array) {
this.array = array;
}
public int[] getArray() {
return array;
}
@Override
public boolean equals(Object object) {
if (this == object) return true;
if (!(object instanceof IntArrayHolder)) return false;
IntArrayHolder that = (IntArrayHolder) object;
return Arrays.equals(array, that.array);
}
@Override
public int hashCode() {
return Arrays.hashCode(array);
}
}
并使用Set<IntArrayHolder>而不是Set<int[]>：
Set<IntArrayHolder> set = new HashSet<>();
set.add(new IntArrayHolder(new int[]{0}));
set.add(new IntArrayHolder(new int[]{0}));
set.add(new IntArrayHolder(new int[]{1}));
set.forEach(elm -> System.out.println(Arrays.toString(elm.getArray()))); // prints [1][0]
您还可以将包装和解包装封装在特殊的泛型类中，并以这种方式使用它们：
Set<int[]> set = new MappedSet<>(new HashSet<>(), Mapper.from(
IntArrayHolder::getArray,
IntArrayHolder::new
));
set.add(new int[]{0});
set.add(new int[]{0});
set.add(new int[]{1});
set.forEach(elm -> System.out.println(Arrays.toString(elm))); // prints [1][0]
这里是Mapper、MappedSet、MappedCollection、MappedIterable和MappedIterator：MappedArray
/**
* <h1>Mapper</h1>
* Represents a two way function which can be used for adapting
* {@code Type<A>} to {@code Type<B>} where {@code Type} is invariant
* generic type.
*
* <h2>Invertibility</h2>
* <p>
* If this mapper isn't bounded result of performing {@code out(in(x))} should
* be similar to {@code x}, no guarantees are made about their equality. The same goes
* with {@code in(out(x))}.
*
* <h2>Nullability</h2>
* <p>
* A mapper always converts {@code null} to {@code null} and non-null references to non-null
* references. {@code null} can be passed to {@link #out(A)} and {@link #in(B)} methods, but
* should never be passed to {@link #doOut(A)} and {@link #doIn(B)}.
*
* <h2>Bounded wildcards</h2>
* <p>
* Bounded wildcards should never be used on {@link A} type parameter, because mapper with bounded
* {@link A} can't be accepted by any adapter and is completely useless.
*
* <p>Using of bounded wildcard on {@link B} type parameter indicates that mapper can perform
* operations in only one way see {@link #outMapper(Function)} and {@link #inMapper(Function)}.
*
* <h2>Unchecked functionality</h2>
* A mapper provides unchecked functionality for not generified methods via {@link #uncheckedOut(Object)},
* {@link #uncheckedIn(Object)} and {@link #unchecked()} methods.
* <p>Restricting unchecked functionality can be done by using {@link #restrictAClass(Class)}
* and {@link #restrictBClass(Class)} methods.
*
* <h2>Instantiation</h2>
* The following factory methods can be used for mapper instantiation:
* <ul>
* <li>{@link #from(Function, Function)} - two ways mapper</li>
* <li>{@link #outMapper(Function)} - only-out mapper</li>
* <li>{@link #inMapper(Function)} - only-in mapper</li>
* </ul>
* <p>This interface can also be implemented from outside.
*
* @param <A> type parameter of adapted generic instance
* @param <B> type parameter of generic adapter
*/
public interface Mapper<A, B> extends Function<A, B> {
/**
* Adapts return value of adapted instance method to adapter type.
*
* @param a result of calling adapted instance method
* @return result which should be return from adapter
* @implNote this method isn't supposed to be overridden, instead {@link #doOut(A)}
* method should be implemented for defining mapper behaviour
*/
@Contract("null -> null; !null -> !null")
@Final
default @Nullable B out(@Nullable A a) {
return a == null ? null : doOut(a);
}
/**
* Adapts input argument of adapter method to adapted instance type.
*
* @param b argument passed to adapter method
* @return argument which should be passed to adapted instance
* @implNote this method isn't supposed to be overridden, instead {@link #doIn(B)}
* method should be implemented for defining mapper behaviour
*/
@Contract("null -> null; !null -> !null")
@Final
default @Nullable A in(@Nullable B b) {
return b == null ? null : doIn(b);
}
/**
* Adapts return value of not generified adapted instance method to adapter type,
* uses unchecked cast.
*
* @param a result of calling adapted instance method, is to have {@link A} type
* @return result which should be return from adapter
* @see #out(A)
*/
@SuppressWarnings("unchecked") // unchecked is indicated in the method name
@Contract("null -> null; !null -> !null")
@Final
default @Nullable B uncheckedOut(@Nullable Object a) {
return out((A) a);
}
/**
* Adapts input argument of not generified adapter method to adapted instance type,
* uses unchecked cast.
*
* @param b argument passed to adapter method, is to have {@link B} type
* @return argument which should be passed to adapted instance
* @see #in(B)
*/
@SuppressWarnings("unchecked") // unchecked is indicated in the method name
@Contract("null -> null; !null -> !null")
@Final
default @Nullable A uncheckedIn(@Nullable Object b) {
return in((B) b);
}
/**
* Performs adapting of {@link A} to {@link B}.
*
* @param a input argument, mustn't be {@code null}
* @return adaptation result, mustn't be {@code null}. If adaptation has failed {@link IllegalArgumentException}
* should be thrown or null-object should be returned.
* @apiNote this method isn't supposed to be called, instead {@link #out(A)} method should be used
* @implNote this method is supposed to be implemented for defining {@link #out(A)} method behaviour
* @see #out(A)
*/
@NotNull B doOut(@NotNull A a);
/**
* Performs adapting of {@link B} to {@link A}.
*
* @param b input argument, mustn't be {@code null}
* @return adaptation result, mustn't be {@code null}. If adaptation has failed {@link IllegalArgumentException}
* should be thrown or null-object should be returned.
* @apiNote this method isn't supposed to be called, instead {@link #in(B)} method should be used
* @implNote this method is supposed to be implemented for defining {@link #in(B)} method behaviour
* @see #in(B)
*/
@NotNull A doIn(@NotNull B b);
/**
* Non-null analog of {@link #out(A)}.
*
* @param a input argument
* @return mapping result
* @apiNote {@code mapper::apply} shouldn't be used, instead mapper instance itself
* should be used as a {@code Function<A, B>}
*/
@Override
default @NotNull B apply(@NotNull A a) {
return out(a);
}
/**
* Non-null analog of {@link #in(B)}.
*
* @param b input argument
* @return mapping result
* @apiNote {@code mapper::undo} shouldn't be used, instead {@link #reverse()}
* should be used as a {@code Function<B, A>}
*/
default @NotNull A undo(@NotNull B b) { return in(b); }
/**
* Returns reverse view of this mapper.
* <p>Some mappers may perform reverse view caching, so it's likely that
* {@code mapper.reverse() == mapper.reverse()} and {@code mapper.reverse().reverse() == mapper}
* will be true.
*
* @return reverse view of this mapper
*/
default Mapper<B, A> reverse() {
return new Mapper<B, A>() {
@Override
public @NotNull A doOut(@NotNull B b) {
return Mapper.this.doIn(b);
}
@Override
public @NotNull B doIn(@NotNull A a) {
return Mapper.this.doOut(a);
}
@Override
public Mapper<A, B> reverse() {
return Mapper.this;
}
};
}
/**
* Returns this mapper after unchecked casting to required type.
* <p>Should be used carefully: sometimes {@link #reverse()}{@code .unchecked()} is required instead
* of {@code unchecked()}.
*
* @param <A2> {@link A} type parameter of returned mapper
* @return this instance
* @see #uncheckedIn(Object)
* @see #uncheckedOut(Object)
*/
@SuppressWarnings("unchecked") // unchecked is indicated in the method name
@Contract(value = "-> this", pure = true)
default <A2> Mapper<A2, B> unchecked() {
return (Mapper<A2, B>) this;
}
@SuppressWarnings("unchecked") // unchecked is indicated in the method name
default <A2, B2> Mapper<A2, B2> doubleUnchecked() {
return (Mapper<A2, B2>) this;
}
/**
* Creates a composed mapper from {@link V} to {@link B} which uses {@code before}
* mapper and this mapper in order required by operations.
*
* @param <V> the first type parameter of {@code before} mapper, and of the
* composed mapper
* @param before the additional mapper
* @return a composed mapper
* @see #andThenMapper(Mapper)
* @see #compose(Function)
*/
@Contract(value = "_ -> new", pure = true)
default <V> Mapper<V, B> composeMapper(Mapper<V, A> before) {
return before.andThenMapper(this);
}
/**
* Creates a composed mapper from {@link A} to {@link C} which uses this
* mapper and {@code after} mapper in order required by operations.
*
* @param <C> the second type parameter of {@code after} mapper, and of the
* composed mapper
* @param after the additional mapper
* @return a composed mapper
* @see #composeMapper(Mapper)
* @see #andThen(Function)
*/
@Contract(value = "_ -> new", pure = true)
default <C> Mapper<A, C> andThenMapper(Mapper<B, C> after) {
return from(a -> after.out(out(a)), c -> in(after.in(c)));
}
/**
* Creates mapper which restricts {@link A} class, so type of {@link #out(A)} operation parameter
* is checked before performing operation.
* <p>If parameter isn't an {@code instanceof clazz} {@link #uncheckedMap(Object)} is used.
*
* @param clazz {@link A} class
* @return mapper which restricts {@link A} class
* @see #restrictBClass(Class)
*/
@Contract(value = "_ -> new", pure = true)
default Mapper<A, B> restrictAClass(Class<A> clazz) {
return from(a -> clazz.isAssignableFrom(a.getClass()) ? doOut(a) : uncheckedMap(a), this::doIn);
}
/**
* Creates mapper which restricts {@link B} class, so type of {@link #in(B)} operation parameter
* is checked before performing operation.
* <p>If parameter isn't an {@code instanceof clazz} {@link #uncheckedMap(Object)} is used.
*
* @param clazz {@link B} class
* @return mapper which restricts {@link B} class
* @see #restrictAClass(Class)
*/
@Contract(value = "_ -> new", pure = true)
default Mapper<A, B> restrictBClass(Class<B> clazz) {
return from(this::doOut, b -> clazz.isAssignableFrom(b.getClass()) ? doIn(b) : uncheckedMap(b));
}
/**
* Creates mapper from given functions.
*
* @param out function for performing {@link #doOut(A)} method
* @param in function for performing {@link #doIn(B)} method
* @param <A> returned mapper first type parameter
* @param <B> returned mapper second type parameter
* @return created mapper
*/
@Contract(value = "_, _ -> new", pure = true)
static <A, B> Mapper<A, B> from(Function<? super A, ? extends B> out, Function<? super B, ? extends A> in) {
return new Mapper<A, B>() {
private @Nullable Mapper<B, A> reverse = null;
@Override
public @NotNull B doOut(@NotNull A a) {
return out.apply(a);
}
@Override
public @NotNull A doIn(@NotNull B b) {
return in.apply(b);
}
@Override
public Mapper<B, A> reverse() {
return (reverse == null) ? (reverse = Mapper.super.reverse()) : reverse;
}
};
}
/**
* Creates mapper that can only normally perform {@link #out(A)} operation.
*
* <p>The returned mapper is bounded so {@link #in(B)} operation without using <i>unchecked functionality</i>
* can only be called with {@code null} argument, according to the contract this will lead to
* returning of {@code null}.
*
* @param out function for performing {@link #doOut(A)} method
* @param <A> returned mapper first type parameter
* @param <B> returned mapper second type parameter
* @return mapper that only provides {@link #out(A)} operation
*/
@Contract(value = "_ -> new", pure = true)
static <A, B> Mapper<A, ? extends B> outMapper(Function<? super A, ? extends B> out) {
return from(out, Mapper::uncheckedMap);
}
/**
* Creates mapper that can only normally perform {@link #in(B)} operation.
*
* <p>The returned mapper is bounded so {@link #out(A)} result can be used only as {@link Object}.
* <p>Returned mapper guarantees that {@code out(x) == x} will always be {@code true}.
*
* @param in function for performing {@link #doIn(B)} method
* @param <A> returned mapper first type parameter
* @param <B> returned mapper second type parameter
* @return mapper that only provides {@link #in(B)} operation
*/
@Contract(value = "_ -> new", pure = true)
static <A, B> Mapper<A, ? super B> inMapper(Function<? super B, ? extends A> in) {
return from(Mapper::uncheckedMap, in);
}
/**
* Creates mapper that maps any object to itself.
*
* @param <T> returned mapper type parameter
* @return created mapper
*/
@Contract(value = "-> new", pure = true)
static <T> Mapper<T, T> identity() {
return from(Function.identity(), Function.identity());
}
/**
* Performs unchecked cast of input to required type,
* this method may also do some logging.
*
* <p>This method is supposed to be used when impossible to call {@code Function<? extends A, B>} or
* returning {@link Object} {@code Function<A, ? super B>} is needed.
*
* <p>In some cases it can also be called when {@code a} appeared to be not an {@code instanceof Class<A>}.
*
* @param a input argument
* @param <A> input argument type
* @param <B> required type
* @return result of unchecked cast
* @deprecated unchecked cast
*/
@SuppressWarnings({"Contract", "unchecked"}) // unchecked is indicated in the method name
@Contract("_ -> param1")
@Deprecated
@WarnOnUse(exceptClasses = Mapper.class)
static <A, B> B uncheckedMap(A a) {
return (B) a;
}
}
public class MappedSet<E, E2> extends MappedCollection<E, E2> implements Set<E2> {
public MappedSet(Set<E> set, Mapper<E, E2> mapper) {
super(set, mapper);
}
public static <E, E2> Set<E2> map(Set<E> inst, Mapper<E, E2> mapper) {
return new MappedSet<>(inst, mapper);
}
public static <E, E2> Set<? extends E2> mapOut(Set<? extends E> inst, Function<? super E, ? extends E2> mapper) {
return map(inst, Mapper.outMapper(mapper));
}
public static <E, E2> Set<? super E2> mapIn(Set<? super E> inst, Function<? super E2, ? extends E> mapper) {
return map(inst, Mapper.inMapper(mapper));
}
}
public class MappedCollection<E, E2> extends MappedIterable<E, E2> implements Collection<E2> {
private final Collection<E> collection;
private final Mapper<E, E2> mapper;
public MappedCollection(Collection<E> collection, Mapper<E, E2> mapper) {
super(collection, mapper);
this.collection = collection;
this.mapper = mapper;
}
public static <E, E2> Collection<E2> map(Collection<E> inst, Mapper<E, E2> mapper) {
return new MappedCollection<>(inst, mapper);
}
public static <E, E2> Collection<? extends E2> mapOut(Collection<? extends E> inst, Function<? super E, ? extends E2> mapper) {
return map(inst, Mapper.outMapper(mapper));
}
public static <E, E2> Collection<? super E2> mapIn(Collection<? super E> inst, Function<? super E2, ? extends E> mapper) {
return map(inst, Mapper.inMapper(mapper));
}
@Override
public int size() {
return collection.size();
}
@Override
public boolean isEmpty() {
return collection.isEmpty();
}
@Override
public boolean contains(Object o) {
return collection.contains(mapper.uncheckedIn(o));
}
@Override
public @NotNull Object[] toArray() {
return MappedArray.map(collection.toArray(), mapper.unchecked());
}
@Override
public @NotNull <T> T[] toArray(@NotNull T[] a) {
return MappedArray.map(collection.toArray(), ContainersUtils.getComponentType(a), mapper.doubleUnchecked());
}
@Contract(mutates = "this")
@Override
public boolean add(@NotNull E2 e2) {
return collection.add(mapper.in(e2));
}
@Contract(mutates = "this")
@Override
public boolean remove(Object o) {
return collection.remove(mapper.uncheckedIn(o));
}
@Override
public boolean containsAll(@NotNull Collection<?> c) {
return collection.containsAll(map(c, mapper.reverse().unchecked()));
}
@Contract(mutates = "this")
@Override
public boolean addAll(@NotNull Collection<? extends E2> c) {
return collection.addAll(mapOut(c, mapper.reverse()));
}
@Contract(mutates = "this")
@Override
public boolean removeAll(@NotNull Collection<?> c) {
return collection.removeAll(map(c, mapper.reverse().unchecked()));
}
@Contract(mutates = "this")
@Override
public boolean retainAll(@NotNull Collection<?> c) {
return collection.retainAll(map(c, mapper.reverse().unchecked()));
}
@Contract(mutates = "this")
@Override
public void clear() {
collection.clear();
}
}
@RequiredArgsConstructor
public class MappedIterable<E, E2> implements Iterable<E2> {
private final @NotNull Iterable<E> iterable;
private final @NotNull Function<? super E, ? extends E2> mapper;
public static <E, E2> Iterator<E2> map(Iterator<E> inst, Function<? super E, ? extends E2> mapper) {
return new MappedIterator<>(inst, mapper);
}
@Override
public @NotNull Iterator<E2> iterator() {
return MappedIterator.map(iterable.iterator(), mapper);
}
}
@RequiredArgsConstructor
public class MappedIterator<E, E2> implements Iterator<E2> {
private final @NotNull Iterator<E> iterator;
private final @NotNull Function<? super E, ? extends E2> mapper;
public static <E, E2> Iterator<E2> map(Iterator<E> inst, Function<? super E, ? extends E2> mapper) {
return new MappedIterator<>(inst, mapper);
}
@Contract(pure = true)
@Override
public boolean hasNext() {
return iterator.hasNext();
}
@Override
public E2 next() {
return mapper.apply(iterator.next());
}
}
@UtilityClass
public class MappedArray {
public static <T> Object[] map(T[] inst, Function<? super T, ?> mapper) {
return Stream.of(inst).map(mapper).toArray();
}
public static <T, T2> T2[] map(T[] inst, Class<T2> clazz, Function<? super T, ? extends T2> mapper) {
return Stream.of(inst).map(mapper).toArray(i -> ContainersUtils.createArray(clazz, i));
}
}
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