Implementing oldData in an ArrayList

Question

I am reading an ArrayList and cannot understand one thing in this method:

public void ensureCapacity(int minCapacity) { modCount++; int oldCapacity = elementData.length; if (minCapacity > oldCapacity) { Object oldData[] = elementData; int newCapacity = (oldCapacity * 3)/2 + 1; if (newCapacity < minCapacity) newCapacity = minCapacity; // minCapacity is usually close to size, so this is a win: elementData = Arrays.copyOf(elementData, newCapacity); } } 

I do not understand what this oldData array oldData used for:

 Object oldData[] = elementData; 

It seems to me that there is absolutely no sense in this local variable inside the ensureCapacity method.

Answer 1

Yes, the line there is completely redundant and left it without refactoring.

It seems that this method was addressed to Java 7 version , and the whole method received refactoring of the logic for increasing the array.

The creators created another method called grow() and moved the logic there from version 7.

 public void ensureCapacity(int minCapacity) { 191 int minExpand = (elementData != EMPTY_ELEMENTDATA) 192 // any size if real element table 193 ? 0 194 // larger than default for empty table. It already supposed to be 195 // at default size. 196 : DEFAULT_CAPACITY; 197 198 if (minCapacity > minExpand) { 199 ensureExplicitCapacity(minCapacity); 200 } 201 } 202 203 private void ensureCapacityInternal(int minCapacity) { 204 if (elementData == EMPTY_ELEMENTDATA) { 205 minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity); 206 } 207 208 ensureExplicitCapacity(minCapacity); 209 } 210 211 private void ensureExplicitCapacity(int minCapacity) { 212 modCount++; 213 214 // overflow-conscious code 215 if (minCapacity - elementData.length > 0) 216 grow(minCapacity); 217 } private void grow(int minCapacity) { 234 // overflow-conscious code 235 int oldCapacity = elementData.length; 236 int newCapacity = oldCapacity + (oldCapacity >> 1); 237 if (newCapacity - minCapacity < 0) 238 newCapacity = minCapacity; 239 if (newCapacity - MAX_ARRAY_SIZE > 0) 240 newCapacity = hugeCapacity(minCapacity); 241 // minCapacity is usually close to size, so this is a win: 242 elementData = Arrays.copyOf(elementData, newCapacity); 243 } 244 245 private static int More ...hugeCapacity(int minCapacity) { 246 if (minCapacity < 0) // overflow 247 throw new OutOfMemoryError(); 248 return (minCapacity > MAX_ARRAY_SIZE) ? 249 Integer.MAX_VALUE : 250 MAX_ARRAY_SIZE; 251 }