JDK7 和JDK8的ArrayList的区别对比

示例

public class ArrayListTest {
    public static void main(String[] args) {
        ArrayList<Object> jdk = new ArrayList<>();
        jdk.add(123);
    }
}

初始化操作
①调用无参构造器

jdk7从无参调用有参构造器，并初始化为10:
/**
 * Constructs an empty list with an initial capacity of ten.
 */
public ArrayList() {
   this(10);
}

/**
 * Constructs an empty list with the specified initial capacity.
 *
 * @param  initialCapacity  the initial capacity of the list
 * @throws IllegalArgumentException if the specified initial capacity
 *         is negative
 */
public ArrayList(int initialCapacity) {
    super();
    if (initialCapacity < 0)
        throw new IllegalArgumentException("Illegal Capacity: "+
                                           initialCapacity);
    this.elementData = new Object[initialCapacity];
}