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see discussion on the core-libs-dev mailing list: http://mail.openjdk.java.net/pipermail/core-libs-dev/2010-March/003694.html Excerpt from this discussion that describes the problem: "I've noticed bugs in java.util.ArrayList, java.util.Hashtable and java.io.ByteArrayOutputStream which arise when the capacities of the data structures reach a particular threshold. More below. When the capacity of an ArrayList reaches (2/3)*Integer.MAX_VALUE its size reaches its capacity and an add or an insert operation is invoked, the capacity is increased by only one element. Notice that in the following excerpt from ArrayList.ensureCapacity the new capacity is set to (3/2) * oldCapacity + 1 unless this value would not suffice to accommodate the required capacity in which case it is set to the required capacity. If the current capacity is at least (2/3)*Integer.MAX_VALUE, then (oldCapacity * 3)/2 + 1 overflows and resolves to a negative number resulting in the new capacity being set to the required capacity. The major consequence of this is that each subsequent add/insert operation results in a full resize of the ArrayList causing performance to degrade significantly. int newCapacity = (oldCapacity * 3)/2 + 1; if (newCapacity < minCapacity) newCapacity = minCapacity; Hashtable breaks entirely when the size of its backing array reaches (1/2) * Integer.MAX_VALUE and a rehash is necessary as is evident from the following excerpt from rehash. Notice that rehash will attempt to create an array of negative size if the size of the backing array reaches (1/2) * Integer.MAX_VALUE since oldCapacity * 2 + 1 overflows and resolves to a negative number. int newCapacity = oldCapacity * 2 + 1; HashtableEntry newTable[] = new HashtableEntry[newCapacity]; When the capacity of the backing array in a ByteArrayOutputStream reaches (1/2) * Integer.MAX_VALUE its size reaches its capacity and a write operation is invoked, the capacity of the backing array is increased only by the required number of elements. Notice that in the following excerpt from ByteArrayOutputStream.write(int) the new backing array capacity is set to 2 * buf.length unless this value would not suffice to accommodate the required capacity in which case it is set to the required capacity. If the current backing array capacity is at least (1/2) * Integer.MAX_VALUE + 1, then buf.length << 1 overflows and resolves to a negative number resulting in the new capacity being set to the required capacity. The major consequence of this, like with ArrayList, is that each subsequent write operation results in a full resize of the ByteArrayOutputStream causing performance to degrade significantly. int newcount = count + 1; if (newcount > buf.length) { buf = Arrays.copyOf(buf, Math.max(buf.length << 1, newcount)); } It is interesting to note that any statements about the amortized time complexity of add/insert operations, such as the one in the ArrayList javadoc, are invalidated by the performance related bugs. One solution to the above situations is to set the new capacity of the backing array to Integer.MAX_VALUE when the initial size calculation results in a negative number during a resize."
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