Arraylist集合 -----添加方法

1、add(E e) 向集合中添加元素

/**

* 檢查數組容量是否夠用

* @param minCapacity

*/

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;

elementData = Arrays.copyOf(elementData, newCapacity);

}

}

}

/* (non-Javadoc)

* 向ArrayList中添加元素

* @see java.util.AbstractList#add(java.lang.Object)

*/

public boolean add(E e){

ensureCapacity(size+1);

elementData[size++] = e;

return true;

}

2、add(int? index ,E e) 向集合的指定索引處添加元素

/**

* 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 {@inheritDoc}

*/

public void add(int index, E element) {

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++;

}

3、addAll(Collection< ? extends E> c) 添加集合

/*

* 添加元素集合

* (non-Javadoc)

* @see java.util.AbstractCollection#addAll(java.util.Collection)

*/

public boolean addAll(Collection extends E> c){

Object[] a = c.toArray();

int numNew = a.length;

ensureCapacity(size+numNew);

System.arraycopy(a, 0, elementData, size, numNew);

size+=numNew;

return numNew!=0;

}

4、addAll(int index, Collection extends E> c); 在指定索引出添加集合

public boolean addAll(int index, Collection extends E> c) {

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;

}

總結

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