10.18 java

1.构造函数

*无参构造函数

public ArrayList() {
    this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}

*一个参数的构造方法，参数为初始的容量

public ArrayList(int initialCapacity) {
        if (initialCapacity > 0) {
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
            this.elementData = EMPTY_ELEMENTDATA;
        } else {
            throw new IllegalArgumentException("Illegal Capacity: "+initialCapacity);
        }
    }

*参数为集合的构造方法

public ArrayList(Collection<? extends E> c) {
        elementData = c.toArray();
        if ((size = elementData.length) != 0) {   
            if (elementData.getClass() != Object[].class)
                elementData = Arrays.copyOf(elementData, size, Object[].class);
        } else {
            this.elementData = EMPTY_ELEMENTDATA;
        }
    }

//ArrayList集合增加元素

import.java.util.AttayList;
import.java.util.List;
piblic class ListDemo {
 public static void main(String[] args) {
  List lis = new ArrayList();
  lis.add("张三");
  lis.add("张三");
  lis.add("李四");
  lis.add("王五");
  System.out.println(lis);
 }
}