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fix ArrayList performance issue

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The ArrayList(Collection) constructor was allocating two arrays
instead of one due to an off-by-one error in ArrayList.grow.  This
commit fixes that and makes grow and shrink more robust.
This commit is contained in:
Joel Dice
2012-06-14 10:55:03 -06:00
parent c00f811a2f
commit 153b78f479
2 changed files with 28 additions and 12 deletions
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25
classpath/java/util/ArrayList.java
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@ -29,14 +29,15 @@ public class ArrayList<T> extends AbstractList<T> implements java.io.Serializabl
addAll(source);
}
private void grow() {
if (array == null || size >= array.length) {
resize(array == null ? MinimumCapacity : array.length * 2);
private void grow(int newSize) {
if (array == null || newSize > array.length) {
resize(Math.max(newSize, array == null
? MinimumCapacity : array.length * 2));
}
}
private void shrink() {
if (array.length / 2 >= MinimumCapacity && size <= array.length / 3) {
private void shrink(int newSize) {
if (array.length / 2 >= MinimumCapacity && newSize <= array.length / 3) {
resize(array.length / 2);
}
}
@ -74,16 +75,15 @@ public class ArrayList<T> extends AbstractList<T> implements java.io.Serializabl
}
public void add(int index, T element) {
size = Math.max(size+1, index+1);
grow();
int newSize = Math.max(size+1, index+1);
grow(newSize);
size = newSize;
System.arraycopy(array, index, array, index+1, size-index-1);
array[index] = element;
}
public boolean add(T element) {
++ size;
grow();
array[size - 1] = element;
add(size, element);
return true;
}
@ -137,8 +137,9 @@ public class ArrayList<T> extends AbstractList<T> implements java.io.Serializabl
System.arraycopy(array, index + 1, array, index, size - index);
}
-- size;
shrink();
int newSize = size - 1;
shrink(newSize);
size = newSize;
return v;
}