[Java] Ensure that Object2*HashMaps and ObjectHashSet always check eq…

…uality using the value in the map and not vice versa. (#253)

* [Java] Ensure that Object2*HashMaps and ObjectHashSet always check equality using the value in the map and not vice versa. This allows implementing asymmetric keys/values which can match multiple other types. For an example see CharSequenceKey from the tests.

* [Java] Refactor map equality tests.

* [Java] Fix Object2ObjectHashMap#containsValue to perform equality check on the value stored rather than the value passed as an argument. Ensure that the equality is always done the same, i.e. use LangUtil#exactEquals.

* [Java] Add sanity tests for Object2IntHashMap and missing value handling.

* [Java] Simplify Object2ObjectHashMap.

* [Java] Fix Object2IntHashMap put/containsKey/removeKey key equality check using the key from the map as the source of the comparison.

* [Java] Avoid loading keys/values/entries multiple times during lookup and bulk operations.

* [Java] Fix EntryIterator/MapEntry equals/hashCode implementations, i.e. handle null values as keys/values and use `Objects.equals` for the equality checks.

* [Java] Replace LangUtil.exactEquals with Objects.equals.

* [Java] Add tests for `Int2Int*Map.compact()`.

* [Java] Suppress lgtm IOOBE warnings.

* [Java] Update LGTM suppression syntax.

(cherry picked from commit a320110)

agrona/src/main/java/org/agrona/BitUtil.java

@@ -171,7 +171,7 @@ public static byte[] fromHexByteArray(final byte[] buffer)
         for (int i = 0; i < buffer.length; i += 2)
         {
             final int hi = FROM_HEX_DIGIT_TABLE[buffer[i]] << 4;
-            final int lo = FROM_HEX_DIGIT_TABLE[buffer[i + 1]]; // lgtm [java/index-out-of-bounds]
+            final int lo = FROM_HEX_DIGIT_TABLE[buffer[i + 1]]; // lgtm[java/index-out-of-bounds]
             outputBuffer[i >> 1] = (byte)(hi | lo);
         }
 

agrona/src/main/java/org/agrona/LangUtil.java

@@ -39,4 +39,5 @@ private static <T extends Throwable> void rethrow(final Throwable t) throws T
     {
         throw (T)t;
     }
+
 }

agrona/src/main/java/org/agrona/collections/BiInt2ObjectMap.java

@@ -164,15 +164,16 @@ public V put(final int keyPartA, final int keyPartB, final V value)
     {
         final long key = compoundKey(keyPartA, keyPartB);
 
-        V oldValue = null;
+        final long[] keys = this.keys;
+        final Object[] values = this.values;
         final int mask = values.length - 1;
         int index = Hashing.hash(key, mask);
 
-        while (null != values[index])
+        Object oldValue;
+        while (null != (oldValue = values[index]))
         {
             if (key == keys[index])
             {
-                oldValue = (V)values[index];
                 break;
             }
 
@@ -192,7 +193,7 @@ public V put(final int keyPartA, final int keyPartB, final V value)
             increaseCapacity();
         }
 
-        return oldValue;
+        return (V)oldValue;
     }
 
     /**
@@ -206,6 +207,8 @@ public V put(final int keyPartA, final int keyPartB, final V value)
     public V get(final int keyPartA, final int keyPartB)
     {
         final long key = compoundKey(keyPartA, keyPartB);
+        final long[] keys = this.keys;
+        final Object[] values = this.values;
         final int mask = values.length - 1;
         int index = Hashing.hash(key, mask);
 
@@ -234,6 +237,8 @@ public V get(final int keyPartA, final int keyPartB)
     public V remove(final int keyPartA, final int keyPartB)
     {
         final long key = compoundKey(keyPartA, keyPartB);
+        final long[] keys = this.keys;
+        final Object[] values = this.values;
         final int mask = values.length - 1;
         int index = Hashing.hash(key, mask);
 
@@ -268,10 +273,10 @@ public V remove(final int keyPartA, final int keyPartB)
     public V computeIfAbsent(final int keyPartA, final int keyPartB, final EntryFunction<? extends V> mappingFunction)
     {
         V value = get(keyPartA, keyPartB);
-        if (value == null)
+        if (null == value)
         {
             value = mappingFunction.apply(keyPartA, keyPartB);
-            if (value != null)
+            if (null != value)
             {
                 put(keyPartA, keyPartB, value);
             }
@@ -290,6 +295,7 @@ public void forEach(final Consumer<V> consumer)
     {
         int remaining = size;
 
+        final Object[] values = this.values;
         for (int i = 0, size = values.length; remaining > 0 && i < size; i++)
         {
             final Object value = values[i];
@@ -311,6 +317,8 @@ public void forEach(final EntryConsumer<V> consumer)
     {
         int remaining = size;
 
+        final long[] keys = this.keys;
+        final Object[] values = this.values;
         for (int i = 0, size = values.length; remaining > 0 && i < size; i++)
         {
             final Object value = values[i];
@@ -354,6 +362,8 @@ public String toString()
         final StringBuilder sb = new StringBuilder();
         sb.append('{');
 
+        final long[] keys = this.keys;
+        final Object[] values = this.values;
         for (int i = 0, size = values.length; i < size; i++)
         {
             final Object value = values[i];
@@ -385,6 +395,8 @@ private void rehash(final int newCapacity)
         final long[] tempKeys = new long[newCapacity];
         final Object[] tempValues = new Object[newCapacity];
 
+        final long[] keys = this.keys;
+        final Object[] values = this.values;
         for (int i = 0, size = values.length; i < size; i++)
         {
             final Object value = values[i];
@@ -403,19 +415,22 @@ private void rehash(final int newCapacity)
             }
         }
 
-        keys = tempKeys;
-        values = tempValues;
+        this.keys = tempKeys;
+        this.values = tempValues;
     }
 
     @SuppressWarnings("FinalParameters")
     private void compactChain(int deleteIndex)
     {
         final int mask = values.length - 1;
         int index = deleteIndex;
+        final long[] keys = this.keys;
+        final Object[] values = this.values;
         while (true)
         {
             index = ++index & mask;
-            if (null == values[index])
+            final Object value = values[index];
+            if (null == value)
             {
                 break;
             }
@@ -427,7 +442,7 @@ private void compactChain(int deleteIndex)
                 (hash <= deleteIndex && deleteIndex <= index))
             {
                 keys[deleteIndex] = key;
-                values[deleteIndex] = values[index];
+                values[deleteIndex] = value;
 
                 values[index] = null;
                 deleteIndex = index;