File	Doc	Category	Size	Date	Package
ArrayList.java	API Doc	Java SE 5 API	21094	Fri Aug 26 14:57:22 BST 2005	java.util

ArrayList

• java.lang.Object
  • java.util.AbstractCollection
    • java.util.AbstractList

List list = Collections.synchronizedList(new ArrayList(...));

Fields Summary
private static final long	serialVersionUID
private transient E[]	elementData The array buffer into which the elements of the ArrayList are stored. The capacity of the ArrayList is the length of this array buffer.
private int	size The size of the ArrayList (the number of elements it contains).

Constructors Summary
public ArrayList(int initialCapacity) Constructs an empty list with the specified initial capacity. param initialCapacity the initial capacity of the list. exception IllegalArgumentException if the specified initial capacity is negative super(); if (initialCapacity < 0) throw new IllegalArgumentException("Illegal Capacity: "+ initialCapacity); this.elementData = (E[])new Object[initialCapacity];
public ArrayList() Constructs an empty list with an initial capacity of ten. this(10);
public ArrayList(Collection c) Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator. The ArrayList instance has an initial capacity of 110% the size of the specified collection. param c the collection whose elements are to be placed into this list. throws NullPointerException if the specified collection is null. size = c.size(); // Allow 10% room for growth elementData = (E[])new Object[ (int)Math.min((size*110L)/100,Integer.MAX_VALUE)]; c.toArray(elementData);

Methods Summary
private void	RangeCheck(int index) Check if the given index is in range. If not, throw an appropriate runtime exception. This method does *not* check if the index is negative: It is always used immediately prior to an array access, which throws an ArrayIndexOutOfBoundsException if index is negative. if (index >= size) throw new IndexOutOfBoundsException( "Index: "+index+", Size: "+size);
public boolean	add(E o) Appends the specified element to the end of this list. param o element to be appended to this list. return true (as per the general contract of Collection.add). ensureCapacity(size + 1); // Increments modCount!! elementData[size++] = o; return true;
public void	add(int index, E element) Inserts the specified element at the specified position in this list. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices). param index index at which the specified element is to be inserted. param element element to be inserted. throws IndexOutOfBoundsException if index is out of range (index < 0 || index > size()). if (index > size || index < 0) throw new IndexOutOfBoundsException( "Index: "+index+", Size: "+size); ensureCapacity(size+1); // Increments modCount!! System.arraycopy(elementData, index, elementData, index + 1, size - index); elementData[index] = element; size++;
public boolean	addAll(java.util.Collection c) Appends all of the elements in the specified Collection to the end of this list, in the order that they are returned by the specified Collection's Iterator. The behavior of this operation is undefined if the specified Collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified Collection is this list, and this list is nonempty.) param c the elements to be inserted into this list. return true if this list changed as a result of the call. throws NullPointerException if the specified collection is null. Object[] a = c.toArray(); int numNew = a.length; ensureCapacity(size + numNew); // Increments modCount System.arraycopy(a, 0, elementData, size, numNew); size += numNew; return numNew != 0;
public boolean	addAll(int index, java.util.Collection c) Inserts all of the elements in the specified Collection into this list, starting at the specified position. Shifts the element currently at that position (if any) and any subsequent elements to the right (increases their indices). The new elements will appear in the list in the order that they are returned by the specified Collection's iterator. param index index at which to insert first element from the specified collection. param c elements to be inserted into this list. return true if this list changed as a result of the call. throws IndexOutOfBoundsException if index out of range (index < 0 || index > size()). throws NullPointerException if the specified Collection is null. if (index > size || index < 0) throw new IndexOutOfBoundsException( "Index: " + index + ", Size: " + size); Object[] a = c.toArray(); int numNew = a.length; ensureCapacity(size + numNew); // Increments modCount int numMoved = size - index; if (numMoved > 0) System.arraycopy(elementData, index, elementData, index + numNew, numMoved); System.arraycopy(a, 0, elementData, index, numNew); size += numNew; return numNew != 0;
public void	clear() Removes all of the elements from this list. The list will be empty after this call returns. modCount++; // Let gc do its work for (int i = 0; i < size; i++) elementData[i] = null; size = 0;
public java.lang.Object	clone() Returns a shallow copy of this ArrayList instance. (The elements themselves are not copied.) return a clone of this ArrayList instance. try { ArrayList<E> v = (ArrayList<E>) super.clone(); v.elementData = (E[])new Object[size]; System.arraycopy(elementData, 0, v.elementData, 0, size); v.modCount = 0; return v; } catch (CloneNotSupportedException e) { // this shouldn't happen, since we are Cloneable throw new InternalError(); }
public boolean	contains(java.lang.Object elem) Returns true if this list contains the specified element. param elem element whose presence in this List is to be tested. return true if the specified element is present; false otherwise. return indexOf(elem) >= 0;
public void	ensureCapacity(int minCapacity) Increases the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument. param minCapacity the desired minimum capacity. modCount++; int oldCapacity = elementData.length; if (minCapacity > oldCapacity) { Object oldData[] = elementData; int newCapacity = (oldCapacity * 3)/2 + 1; if (newCapacity < minCapacity) newCapacity = minCapacity; elementData = (E[])new Object[newCapacity]; System.arraycopy(oldData, 0, elementData, 0, size); }
private void	fastRemove(int index) modCount++; int numMoved = size - index - 1; if (numMoved > 0) System.arraycopy(elementData, index+1, elementData, index, numMoved); elementData[--size] = null; // Let gc do its work
public E	get(int index) Returns the element at the specified position in this list. param index index of element to return. return the element at the specified position in this list. throws IndexOutOfBoundsException if index is out of range (index < 0 || index >= size()). RangeCheck(index); return elementData[index];
public int	indexOf(java.lang.Object elem) Searches for the first occurence of the given argument, testing for equality using the equals method. param elem an object. return the index of the first occurrence of the argument in this list; returns -1 if the object is not found. see Object#equals(Object) if (elem == null) { for (int i = 0; i < size; i++) if (elementData[i]==null) return i; } else { for (int i = 0; i < size; i++) if (elem.equals(elementData[i])) return i; } return -1;
public boolean	isEmpty() Tests if this list has no elements. return true if this list has no elements; false otherwise. return size == 0;
public int	lastIndexOf(java.lang.Object elem) Returns the index of the last occurrence of the specified object in this list. param elem the desired element. return the index of the last occurrence of the specified object in this list; returns -1 if the object is not found. if (elem == null) { for (int i = size-1; i >= 0; i--) if (elementData[i]==null) return i; } else { for (int i = size-1; i >= 0; i--) if (elem.equals(elementData[i])) return i; } return -1;
private void	readObject(java.io.ObjectInputStream s) Reconstitute the ArrayList instance from a stream (that is, deserialize it). // Read in size, and any hidden stuff s.defaultReadObject(); // Read in array length and allocate array int arrayLength = s.readInt(); Object[] a = elementData = (E[])new Object[arrayLength]; // Read in all elements in the proper order. for (int i=0; i<size; i++) a[i] = s.readObject();
public E	remove(int index) Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices). param index the index of the element to removed. return the element that was removed from the list. throws IndexOutOfBoundsException if index out of range (index < 0 || index >= size()). RangeCheck(index); modCount++; E oldValue = elementData[index]; int numMoved = size - index - 1; if (numMoved > 0) System.arraycopy(elementData, index+1, elementData, index, numMoved); elementData[--size] = null; // Let gc do its work return oldValue;
public boolean	remove(java.lang.Object o) Removes a single instance of the specified element from this list, if it is present (optional operation). More formally, removes an element e such that (o==null ? e==null : o.equals(e)), if the list contains one or more such elements. Returns true if the list contained the specified element (or equivalently, if the list changed as a result of the call). param o element to be removed from this list, if present. return true if the list contained the specified element. if (o == null) { for (int index = 0; index < size; index++) if (elementData[index] == null) { fastRemove(index); return true; } } else { for (int index = 0; index < size; index++) if (o.equals(elementData[index])) { fastRemove(index); return true; } } return false;
protected void	removeRange(int fromIndex, int toIndex) Removes from this List all of the elements whose index is between fromIndex, inclusive and toIndex, exclusive. Shifts any succeeding elements to the left (reduces their index). This call shortens the list by (toIndex - fromIndex) elements. (If toIndex==fromIndex, this operation has no effect.) param fromIndex index of first element to be removed. param toIndex index after last element to be removed. modCount++; int numMoved = size - toIndex; System.arraycopy(elementData, toIndex, elementData, fromIndex, numMoved); // Let gc do its work int newSize = size - (toIndex-fromIndex); while (size != newSize) elementData[--size] = null;
public E	set(int index, E element) Replaces the element at the specified position in this list with the specified element. param index index of element to replace. param element element to be stored at the specified position. return the element previously at the specified position. throws IndexOutOfBoundsException if index out of range (index < 0 || index >= size()). RangeCheck(index); E oldValue = elementData[index]; elementData[index] = element; return oldValue;
public int	size() Returns the number of elements in this list. return the number of elements in this list. return size;
public java.lang.Object[]	toArray() Returns an array containing all of the elements in this list in the correct order. return an array containing all of the elements in this list in the correct order. Object[] result = new Object[size]; System.arraycopy(elementData, 0, result, 0, size); return result;
public T[]	toArray(T[] a) Returns an array containing all of the elements in this list in the correct order; the runtime type of the returned array is that of the specified array. If the list fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this list. If the list fits in the specified array with room to spare (i.e., the array has more elements than the list), the element in the array immediately following the end of the collection is set to null. This is useful in determining the length of the list only if the caller knows that the list does not contain any null elements. param a the array into which the elements of the list are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose. return an array containing the elements of the list. throws ArrayStoreException if the runtime type of a is not a supertype of the runtime type of every element in this list. if (a.length < size) a = (T[])java.lang.reflect.Array. newInstance(a.getClass().getComponentType(), size); System.arraycopy(elementData, 0, a, 0, size); if (a.length > size) a[size] = null; return a;
public void	trimToSize() Trims the capacity of this ArrayList instance to be the list's current size. An application can use this operation to minimize the storage of an ArrayList instance. modCount++; int oldCapacity = elementData.length; if (size < oldCapacity) { Object oldData[] = elementData; elementData = (E[])new Object[size]; System.arraycopy(oldData, 0, elementData, 0, size); }
private void	writeObject(java.io.ObjectOutputStream s) Save the state of the ArrayList instance to a stream (that is, serialize it). serialData The length of the array backing the ArrayList instance is emitted (int), followed by all of its elements (each an Object) in the proper order. int expectedModCount = modCount; // Write out element count, and any hidden stuff s.defaultWriteObject(); // Write out array length s.writeInt(elementData.length); // Write out all elements in the proper order. for (int i=0; i<size; i++) s.writeObject(elementData[i]); if (modCount != expectedModCount) { throw new ConcurrentModificationException(); }