com.google.common.collect.ImmutableMap Maven / Gradle / Ivy
/*
* 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.collect;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.Iterables.getOnlyElement;
import com.google.common.annotations.GwtCompatible;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.annotation.Nullable;
/**
* An immutable, hash-based {@link Map} with reliable user-specified iteration
* order. Does not permit null keys or values.
*
* Unlike {@link Collections#unmodifiableMap}, which is a view of a
* separate map which can still change, an instance of {@code ImmutableMap}
* contains its own data and will never change. {@code ImmutableMap} is
* convenient for {@code public static final} maps ("constant maps") and also
* lets you easily make a "defensive copy" of a map provided to your class by a
* caller.
*
*
Performance notes: unlike {@link HashMap}, {@code ImmutableMap} is
* not optimized for element types that have slow {@link Object#equals} or
* {@link Object#hashCode} implementations. You can get better performance by
* having your element type cache its own hash codes, and by making use of the
* cached values to short-circuit a slow {@code equals} algorithm.
*
*
See the Guava User Guide article on
* immutable collections.
*
* @author Jesse Wilson
* @author Kevin Bourrillion
* @since 2.0 (imported from Google Collections Library)
*/
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // we're overriding default serialization
public abstract class ImmutableMap implements Map, Serializable {
/**
* Returns the empty map. This map behaves and performs comparably to
* {@link Collections#emptyMap}, and is preferable mainly for consistency
* and maintainability of your code.
*/
// Casting to any type is safe because the set will never hold any elements.
@SuppressWarnings("unchecked")
public static ImmutableMap of() {
return (ImmutableMap) EmptyImmutableMap.INSTANCE;
}
/**
* Returns an immutable map containing a single entry. This map behaves and
* performs comparably to {@link Collections#singletonMap} but will not accept
* a null key or value. It is preferable mainly for consistency and
* maintainability of your code.
*/
public static ImmutableMap of(K k1, V v1) {
return new SingletonImmutableMap(
checkNotNull(k1), checkNotNull(v1));
}
/**
* Returns an immutable map containing the given entries, in order.
*
* @throws IllegalArgumentException if duplicate keys are provided
*/
public static ImmutableMap of(K k1, V v1, K k2, V v2) {
return new RegularImmutableMap(entryOf(k1, v1), entryOf(k2, v2));
}
/**
* Returns an immutable map containing the given entries, in order.
*
* @throws IllegalArgumentException if duplicate keys are provided
*/
public static ImmutableMap of(
K k1, V v1, K k2, V v2, K k3, V v3) {
return new RegularImmutableMap(
entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3));
}
/**
* Returns an immutable map containing the given entries, in order.
*
* @throws IllegalArgumentException if duplicate keys are provided
*/
public static ImmutableMap of(
K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
return new RegularImmutableMap(
entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3), entryOf(k4, v4));
}
/**
* Returns an immutable map containing the given entries, in order.
*
* @throws IllegalArgumentException if duplicate keys are provided
*/
public static ImmutableMap of(
K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
return new RegularImmutableMap(entryOf(k1, v1),
entryOf(k2, v2), entryOf(k3, v3), entryOf(k4, v4), entryOf(k5, v5));
}
// looking for of() with > 5 entries? Use the builder instead.
/**
* Returns a new builder. The generated builder is equivalent to the builder
* created by the {@link Builder} constructor.
*/
public static Builder builder() {
return new Builder();
}
/**
* Verifies that {@code key} and {@code value} are non-null, and returns a new
* immutable entry with those values.
*
* A call to {@link Map.Entry#setValue} on the returned entry will always
* throw {@link UnsupportedOperationException}.
*/
static Entry entryOf(K key, V value) {
checkNotNull(key, "null key in entry: null=%s", value);
checkNotNull(value, "null value in entry: %s=null", key);
return Maps.immutableEntry(key, value);
}
/**
* A builder for creating immutable map instances, especially {@code public
* static final} maps ("constant maps"). Example: {@code
*
* static final ImmutableMap WORD_TO_INT =
* new ImmutableMap.Builder()
* .put("one", 1)
* .put("two", 2)
* .put("three", 3)
* .build();}
*
* For small immutable maps, the {@code ImmutableMap.of()} methods are
* even more convenient.
*
* Builder instances can be reused - it is safe to call {@link #build}
* multiple times to build multiple maps in series. Each map is a superset of
* the maps created before it.
*
* @since 2.0 (imported from Google Collections Library)
*/
public static class Builder {
final ArrayList> entries = Lists.newArrayList();
/**
* Creates a new builder. The returned builder is equivalent to the builder
* generated by {@link ImmutableMap#builder}.
*/
public Builder() {}
/**
* Associates {@code key} with {@code value} in the built map. Duplicate
* keys are not allowed, and will cause {@link #build} to fail.
*/
public Builder put(K key, V value) {
entries.add(entryOf(key, value));
return this;
}
/**
* Adds the given {@code entry} to the map, making it immutable if
* necessary. Duplicate keys are not allowed, and will cause {@link #build}
* to fail.
*
* @since 11.0
*/
public Builder put(Entry entry) {
K key = entry.getKey();
V value = entry.getValue();
if (entry instanceof ImmutableEntry) {
checkNotNull(key);
checkNotNull(value);
@SuppressWarnings("unchecked") // all supported methods are covariant
Entry immutableEntry = (Entry) entry;
entries.add(immutableEntry);
} else {
// Directly calling entryOf(entry.getKey(), entry.getValue()) can cause
// compilation error in Eclipse.
entries.add(entryOf(key, value));
}
return this;
}
/**
* Associates all of the given map's keys and values in the built map.
* Duplicate keys are not allowed, and will cause {@link #build} to fail.
*
* @throws NullPointerException if any key or value in {@code map} is null
*/
public Builder putAll(Map map) {
entries.ensureCapacity(entries.size() + map.size());
for (Entry entry : map.entrySet()) {
put(entry.getKey(), entry.getValue());
}
return this;
}
/*
* TODO(kevinb): Should build() and the ImmutableBiMap & ImmutableSortedMap
* versions throw an IllegalStateException instead?
*/
/**
* Returns a newly-created immutable map.
*
* @throws IllegalArgumentException if duplicate keys were added
*/
public ImmutableMap build() {
return fromEntryList(entries);
}
private static ImmutableMap fromEntryList(
List> entries) {
int size = entries.size();
switch (size) {
case 0:
return of();
case 1:
return new SingletonImmutableMap(getOnlyElement(entries));
default:
Entry[] entryArray
= entries.toArray(new Entry[entries.size()]);
return new RegularImmutableMap(entryArray);
}
}
}
/**
* Returns an immutable map containing the same entries as {@code map}. If
* {@code map} somehow contains entries with duplicate keys (for example, if
* it is a {@code SortedMap} whose comparator is not consistent with
* equals), the results of this method are undefined.
*
* Despite the method name, this method attempts to avoid actually copying
* the data when it is safe to do so. The exact circumstances under which a
* copy will or will not be performed are undocumented and subject to change.
*
* @throws NullPointerException if any key or value in {@code map} is null
*/
public static ImmutableMap copyOf(
Map map) {
if ((map instanceof ImmutableMap) && !(map instanceof ImmutableSortedMap)) {
// TODO(user): Make ImmutableMap.copyOf(immutableBiMap) call copyOf()
// on the ImmutableMap delegate(), rather than the bimap itself
@SuppressWarnings("unchecked") // safe since map is not writable
ImmutableMap kvMap = (ImmutableMap) map;
if (!kvMap.isPartialView()) {
return kvMap;
}
}
@SuppressWarnings("unchecked") // we won't write to this array
Entry[] entries = map.entrySet().toArray(new Entry[0]);
switch (entries.length) {
case 0:
return of();
case 1:
return new SingletonImmutableMap(entryOf(
entries[0].getKey(), entries[0].getValue()));
default:
for (int i = 0; i < entries.length; i++) {
K k = entries[i].getKey();
V v = entries[i].getValue();
entries[i] = entryOf(k, v);
}
return new RegularImmutableMap(entries);
}
}
ImmutableMap() {}
/**
* Guaranteed to throw an exception and leave the map unmodified.
*
* @throws UnsupportedOperationException always
*/
@Override
public final V put(K k, V v) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the map unmodified.
*
* @throws UnsupportedOperationException always
*/
@Override
public final V remove(Object o) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the map unmodified.
*
* @throws UnsupportedOperationException always
*/
@Override
public final void putAll(Map map) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the map unmodified.
*
* @throws UnsupportedOperationException always
*/
@Override
public final void clear() {
throw new UnsupportedOperationException();
}
@Override
public boolean isEmpty() {
return size() == 0;
}
@Override
public boolean containsKey(@Nullable Object key) {
return get(key) != null;
}
@Override
public boolean containsValue(@Nullable Object value) {
return value != null && Maps.containsValueImpl(this, value);
}
// Overriding to mark it Nullable
@Override
public abstract V get(@Nullable Object key);
private transient ImmutableSet> entrySet;
/**
* Returns an immutable set of the mappings in this map. The entries are in
* the same order as the parameters used to build this map.
*/
@Override
public ImmutableSet> entrySet() {
ImmutableSet> result = entrySet;
return (result == null) ? entrySet = createEntrySet() : result;
}
abstract ImmutableSet> createEntrySet();
private transient ImmutableSet keySet;
/**
* Returns an immutable set of the keys in this map. These keys are in
* the same order as the parameters used to build this map.
*/
@Override
public ImmutableSet keySet() {
ImmutableSet result = keySet;
return (result == null) ? keySet = createKeySet() : result;
}
ImmutableSet createKeySet() {
return new ImmutableMapKeySet(entrySet()) {
@Override ImmutableMap map() {
return ImmutableMap.this;
}
};
}
private transient ImmutableCollection values;
/**
* Returns an immutable collection of the values in this map. The values are
* in the same order as the parameters used to build this map.
*/
@Override
public ImmutableCollection values() {
ImmutableCollection result = values;
return (result == null) ? values = createValues() : result;
}
ImmutableCollection createValues() {
return new ImmutableMapValues() {
@Override ImmutableMap map() {
return ImmutableMap.this;
}
};
}
@Override public boolean equals(@Nullable Object object) {
return Maps.equalsImpl(this, object);
}
abstract boolean isPartialView();
@Override public int hashCode() {
// not caching hash code since it could change if map values are mutable
// in a way that modifies their hash codes
return entrySet().hashCode();
}
@Override public String toString() {
return Maps.toStringImpl(this);
}
/**
* Serialized type for all ImmutableMap instances. It captures the logical
* contents and they are reconstructed using public factory methods. This
* ensures that the implementation types remain as implementation details.
*/
static class SerializedForm implements Serializable {
private final Object[] keys;
private final Object[] values;
SerializedForm(ImmutableMap map) {
keys = new Object[map.size()];
values = new Object[map.size()];
int i = 0;
for (Entry entry : map.entrySet()) {
keys[i] = entry.getKey();
values[i] = entry.getValue();
i++;
}
}
Object readResolve() {
Builder builder = new Builder();
return createMap(builder);
}
Object createMap(Builder builder) {
for (int i = 0; i < keys.length; i++) {
builder.put(keys[i], values[i]);
}
return builder.build();
}
private static final long serialVersionUID = 0;
}
Object writeReplace() {
return new SerializedForm(this);
}
}