ArrayList源代码分析
在util包内
package java.util;
继承AbstractList,实现List ,RandomAccess,Cloneable,Serializable
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
属性:
private transient Object[] elementData; //对象数组
private int size; //长度
方法:
//构造方法
public ArrayList(int initialCapacity) { //initialCapacity为初始分配容量
super(); //父类实现 为空方法
if (initialCapacity < 0) //正数判断
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
this.elementData = new Object[initialCapacity]; //分配数组
}
public ArrayList() {
this(10); //无参构造方法,带10个容量
}
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
size = elementData.length;
// c.toArray might (incorrectly) not return Object[] (see 6260652)
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
}
public void trimToSize() { //将此 ArrayList 实例的容量调整为列表的当前大小。
modCount++;
int oldCapacity = elementData.length;
if (size < oldCapacity) {
elementData = Arrays.copyOf(elementData, size);
}
}
调整容量大小
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);
}
}
返回容量大小
public int size() {
return size;
}
判断是否为空
public boolean isEmpty() {
return size == 0;
}
是否包含元素
public boolean contains(Object o) {
return indexOf(o) >= 0;
}
查找第一个相同元素的位置
public int indexOf(Object o) {
if (o == null) { //如果为空
for (int i = 0; i < size; i++) //遍历数组
if (elementData[i]==null)
return i;
} else {
for (int i = 0; i < size; i++) //遍历数组
if (o.equals(elementData[i]))
return i;
}
return -1; //找不到返回-1
}
查找最后一个相同元素的位置
public int lastIndexOf(Object o) {
if (o == null) { //如果为空
for (int i = size-1; i >= 0; i--) //遍历数组
if (elementData[i]==null)
return i;
} else {
for (int i = size-1; i >= 0; i--) //遍历数组
if (o.equals(elementData[i]))
return i;
}
return -1; //找不到返回-1
}