java.util.Map#compute ( )源码实例Demo

@Test(dataProvider = "caches")
@CacheSpec(population = Population.FULL, expiryTime = Expire.ONE_MINUTE,
    mustExpireWithAnyOf = { AFTER_WRITE, VARIABLE },
    expiry = { CacheExpiry.DISABLED, CacheExpiry.WRITE },
    expireAfterWrite = {Expire.DISABLED, Expire.ONE_MINUTE})
public void compute_writeTime(Map<Integer, Integer> map, CacheContext context) {
  Integer key = context.firstKey();
  Integer value = context.absentValue();

  map.compute(key, (k, v) -> {
    context.ticker().advance(5, TimeUnit.MINUTES);
    return value;
  });
  context.cleanUp();
  assertThat(map.size(), is(1));
  assertThat(map.containsKey(key), is(true));
}
 

public static char firstNonRepeatedCharacterV3(String str) {

        if (str == null || str.isBlank()) {
            // or throw IllegalArgumentException
            return Character.MIN_VALUE;
        }

        Map<Character, Integer> chars = new LinkedHashMap<>();

        // or use for(char ch: str.toCharArray()) { ... }
        for (int i = 0; i < str.length(); i++) {
            char ch = str.charAt(i);

            chars.compute(ch, (k, v) -> (v == null) ? 1 : ++v);
        }

        for (Map.Entry<Character, Integer> entry : chars.entrySet()) {
            if (entry.getValue() == 1) {
                return entry.getKey();
            }
        }

        return Character.MIN_VALUE;
    }
 

Map<Integer, WordPosFrequencies> byWordLength() {
  Map<Integer, Map<String, Map<PartOfSpeech, Integer>>> builder = new HashMap<>();
  for (String s : getWords()) {
    int length = s.length();
    builder.compute(length, (Integer k, @Nullable Map<String, Map<PartOfSpeech, Integer>> v) -> {
      if (v == null) {
        v = new HashMap<>();
      }
      v.put(s, posFrequenciesForWord.get(s));
      return v;
    });
  }
  return builder.entrySet()
      .stream()
      .collect(Collectors.toMap(Map.Entry::getKey, e -> bySumming(e.getValue())));
}
 

/**
 * Merges the {@link MethodInfo}s with the same method name and {@link HttpMethod} pair
 * into a single {@link MethodInfo}. Note that only the {@link EndpointInfo}s are merged
 * because the {@link MethodInfo}s being merged always have the same
 * {@code exampleHttpHeaders} and {@code exampleRequests}.
 */
@VisibleForTesting
static Set<MethodInfo> mergeEndpoints(Iterable<MethodInfo> methodInfos) {
    final Map<List<Object>, MethodInfo> methodInfoMap = new HashMap<>();
    for (MethodInfo methodInfo : methodInfos) {
        final List<Object> mergeKey = ImmutableList.of(methodInfo.name(), methodInfo.httpMethod());
        methodInfoMap.compute(mergeKey, (key, value) -> {
            if (value == null) {
                return methodInfo;
            } else {
                final Set<EndpointInfo> endpointInfos =
                        Sets.union(value.endpoints(), methodInfo.endpoints());
                return new MethodInfo(value.name(), value.returnTypeSignature(),
                                      value.parameters(), value.exceptionTypeSignatures(),
                                      endpointInfos, value.exampleHttpHeaders(),
                                      value.exampleRequests(), value.examplePaths(), value.exampleQueries(),
                                      value.httpMethod(), value.docString());
            }
        });
    }
    return ImmutableSortedSet
            .orderedBy(comparing(MethodInfo::name).thenComparing(MethodInfo::httpMethod))
            .addAll(methodInfoMap.values())
            .build();
}
 

@Test
public void testMapCompute(){
	Map<String, String> map = new HashMap<>();
	String putValue = "putValue";
	String val = map.compute("test", (k, v)-> v==null?putValue:v+putValue);
	Assert.assertEquals(putValue, val);
	
	val = map.put("test", "putValue2");
	Assert.assertEquals("putValue", val);
	
	val = map.compute("test", (k, v)-> v==null?putValue:v+putValue);
	Assert.assertEquals("putValue2"+putValue, val);
	
	val = map.computeIfPresent("test2", (k, v)-> putValue);
	Assert.assertTrue(val==null);
	
	val = map.computeIfAbsent("test2", (v)-> putValue);
	Assert.assertEquals(putValue, val);
	val = map.computeIfPresent("test2", (k, v)-> v+putValue);
	Assert.assertEquals(putValue+putValue, val);
}
 

public @Nullable TreeNode tryInsert(String s) {
    Map<String, TreeNode> childMap = getChildMap();
    if (!allowInsert(this)) {
        return null;
    }

    return childMap.compute(s, (key, prev) -> {
        if (prev != null) {
            return prev;
        }

        // dirty the cache & return a new node
        this.cachedDeepSize = Integer.MIN_VALUE;
        return new TreeNode(this);
    });
}
 

@Override
public void render(MatrixStack stack, VertexConsumerProvider renderContext, int lightUv, T entity, float limbDistance, float limbAngle, float tickDelta, float age, float headYaw, float headPitch) {

    if (entity.isInvisible()) {
        return;
    }

    M model = getModelWrapper().getBody();

    Map<BodyPart, Float> renderStackingOffsets = new HashMap<>();

    for (Map.Entry<Wearable, IGear> entry : gears.entrySet()) {
        Wearable wearable = entry.getKey();
        IGear gear = entry.getValue();

        if (getContext().shouldRender(model, entity, wearable, gear)) {
            stack.push();
            model.transform(gear.getGearLocation(), stack);
            model.getBodyPart(gear.getGearLocation()).rotate(stack);

            if (gear instanceof IStackable) {
                BodyPart part = gear.getGearLocation();
                renderStackingOffsets.compute(part, (k, v) -> {
                    float offset = ((IStackable)gear).getStackingOffset();
                    if (v != null) {
                        stack.translate(0, -v, 0);
                        offset += v;
                    }
                    return offset;
                });
            }

            renderGear(model, entity, gear, stack, renderContext, lightUv, limbDistance, limbAngle, tickDelta);
            stack.pop();
        }
    }
}
 

private <K, V> void multimapPut(Map<K, List<V>> map, K key, V value) {
  map.compute(key, (unused, v) -> {
    if (v == null) {
      v = new ArrayList<>();
    }
    v.add(value);
    return v;
  });
}
 

public static <K, V> void addAllOrdered(Map<K, List<V>> multiMap, K key, List<V> values) {
  multiMap.compute(key, (key_, values_) -> {
    List<V> valuesMerged = values_ != null ? values_ : new ArrayList<>(values.size());
    valuesMerged.addAll(values);
    return valuesMerged;
  });
}
 

private Map<String, Object> bundleOptions() {
    Map<String, Object> options = new HashMap<>();
    options.compute(PROTOCOL, value(this::getProtocol));
    options.compute(SECURE_TYPE, value(this::getSecureType));
    options.compute(HOST, value(this::getHost));
    options.compute(PORT, value(this::getPort));
    options.compute(USER, value(this::getUsername));
    options.compute(PASSWORD, value(this::getPassword));
    options.compute(FOLDER, value(this::getFolderName));
    options.compute(SERVER_CERTIFICATE, value(this::getServerCertificate));
    options.compute(UNSEEN_ONLY, value(this::isUnseenOnly));
    options.compute(DELAY, value(this::getDelay));
    options.compute(MAX_MESSAGES, value(this::getMaxResults));
    return options;
}
 

/**
 * Returns the available {@link Application} and their model artifact metadata.
 *
 * @return the available {@link Application} and their model artifact metadata
 * @throws IOException if failed to download to repository metadata
 * @throws ModelNotFoundException if failed to parse repository metadata
 */
static Map<Application, List<Artifact>> listModels()
        throws IOException, ModelNotFoundException {
    @SuppressWarnings("PMD.UseConcurrentHashMap")
    Map<Application, List<Artifact>> models =
            new TreeMap<>(Comparator.comparing(Application::getPath));
    ServiceLoader<ZooProvider> providers = ServiceLoader.load(ZooProvider.class);
    for (ZooProvider provider : providers) {
        ModelZoo zoo = provider.getModelZoo();
        if (zoo == null) {
            continue;
        }
        List<ModelLoader<?, ?>> list = zoo.getModelLoaders();
        for (ModelLoader<?, ?> loader : list) {
            Application app = loader.getApplication();
            final List<Artifact> artifacts = loader.listModels();
            models.compute(
                    app,
                    (key, val) -> {
                        if (val == null) {
                            val = new ArrayList<>();
                        }
                        val.addAll(artifacts);
                        return val;
                    });
        }
    }
    return models;
}
 

/**
 * Resolves all keys within the given chain to their equivalent put operations.
 *
 * @param chain target chain
 * @return a map of equivalent put operations
 */
protected Map<K, PutOperation<K, V>> resolveAll(Chain chain) {
  //absent hash-collisions this should always be a 1 entry map
  Map<K, PutOperation<K, V>> compacted = new HashMap<>(2);
  for (Element element : chain) {
    ByteBuffer payload = element.getPayload();
    Operation<K, V> operation = codec.decode(payload);
    compacted.compute(operation.getKey(), (k, v) -> applyOperation(k, v, operation));
  }
  return compacted;
}
 

private void shouldBeEmpty(final Graph<Node, Edge> givenGraph, final AssertionErrorCollector errorCollector) {
    final Map<String, Integer> unexpectedNodesOccurence = new HashMap<>();

    for (final Node node : givenGraph.vertexSet()) {
        unexpectedNodesOccurence.compute(node.getType(), (k, v) -> v == null ? 1 : v + 1);
    }

    for (final Entry<String, Integer> nodeEntries : unexpectedNodesOccurence.entrySet()) {
        if (nodeEntries.getValue() != 0) {
            errorCollector.collect("No nodes with " + nodeEntries.getKey() + " labels were expected, but there are <"
                    + nodeEntries.getValue() + "> nodes present.");
        }
    }
}
 

public void test_CheckedMap_compute() {
    Map<Integer, Double> map = new HashMap<>();
    Map checkedMap = Collections.checkedMap(map, Integer.class, Double.class);
    MapDefaultMethodTester.test_compute(checkedMap, true /* acceptsNullKey */);

    Map checkedMap2 = Collections.checkedMap(new HashMap(), Integer.class, String.class);
    checkedMap2.put(1, A_STRING);
    try {
        checkedMap2.compute(1, (k, v) -> NOT_A_STRING);
        fail();
    } catch (ClassCastException expected) {}
}
 

@Test
public void decayTest() {
    final int N = 1000;
    final int ITEMS = 100;
    final double DECAY = .5;
    final int CAPACITY = 15;
    final double EPSILON = 1.0/CAPACITY;

    AmortizedMaintenanceCounter ss = new AmortizedMaintenanceCounter(CAPACITY);

    Random r = new Random(0);

    Map<Integer, Double> trueCnt = new HashMap<>();

    for (int i = 0; i < N; ++i) {
        int item = r.nextInt(ITEMS);
        ss.observe(item);

        trueCnt.compute(item, (k, v) -> v == null ? 1 : v + 1);

        if (i % 10 == 0) {
            ss.multiplyAllCounts(DECAY);

            trueCnt.forEach((k, v) -> trueCnt.put(k, v*DECAY));
        }
    }

    Map<Integer, Double> cnts = ss.getCounts();

    for (Map.Entry<Integer, Double> cnt : cnts.entrySet()) {
        assertEquals(trueCnt.get(cnt.getKey()), cnt.getValue(), N*EPSILON);
    }

    int key = cnts.keySet().iterator().next();
    assertEquals(cnts.get(key), ss.getCount(key), 1e-10);
}
 

public static <K, V> void addOrdered(Map<K, List<V>> multiMap, K key, V value) {
  multiMap.compute(key, (key_, values_) -> {
    List<V> valuesMerged = values_ != null ? values_ : new ArrayList<>(1);
    valuesMerged.add(value);
    return valuesMerged;
  });
}
 

public static <K, V> void addAll(Map<K, Collection<V>> multiMap, K key, Collection<V> values) {
  multiMap.compute(key, (key_, values_) -> {
    Collection<V> valuesMerged = values_ != null ? values_ : new ArrayList<>(values.size());
    valuesMerged.addAll(values);
    return valuesMerged;
  });
}
 

public static <K, V> void add(Map<K, Collection<V>> multiMap, K key, V value) {
  multiMap.compute(key, (key_, values_) -> {
    Collection<V> valuesMerged = values_ != null ? values_ : new ArrayList<>(1);
    valuesMerged.add(value);
    return valuesMerged;
  });
}
 

private void DFS(Set<Vertex<T>> visited,
        Set<Vertex<T>> articulationPoints, Vertex<T> vertex,
        Map<Vertex<T>, Integer> visitedTime,
        Map<Vertex<T>, Integer> lowTime, Map<Vertex<T>, Vertex<T>> parent) {
    visited.add(vertex);
    visitedTime.put(vertex, time);
    lowTime.put(vertex, time);
    time++;
    int childCount =0;
    boolean isArticulationPoint = false;
    for(Vertex<T> adj : vertex.getAdjacentVertexes()){
        //if adj is same as parent then just ignore this vertex.
        if(adj.equals(parent.get(vertex))) {
            continue;
        }
        //if adj has not been visited then visit it.
        if(!visited.contains(adj)) {
            parent.put(adj, vertex);
            childCount++;
            DFS(visited, articulationPoints, adj, visitedTime, lowTime, parent);

            if(visitedTime.get(vertex) <= lowTime.get(adj)) {
                isArticulationPoint = true;
            } else {
                //below operation basically does lowTime[vertex] = min(lowTime[vertex], lowTime[adj]);
                lowTime.compute(vertex, (currentVertex, time) ->
                    Math.min(time, lowTime.get(adj))
                );
            }

        } else { //if adj is already visited see if you can get better low time.
            //below operation basically does lowTime[vertex] = min(lowTime[vertex], visitedTime[adj]);
            lowTime.compute(vertex, (currentVertex, time) ->
                            Math.min(time, visitedTime.get(adj))
            );
        }
    }

    //checks if either condition 1 or condition 2 meets). If yes then it is articulation point.
    if((parent.get(vertex) == null && childCount >= 2) || parent.get(vertex) != null && isArticulationPoint ) {
        articulationPoints.add(vertex);
    }
    
}
 

private void processResource(FHIRRegistryResource registryResource, Map<String,Set<Canonical>> resourceTypeWithCanonicalUrls) {
    String type = registryResource.getType();
    resourceTypeWithCanonicalUrls.compute(type, (k,v) -> checkOrCreateSet(k,v,registryResource));
}