List toArray() toArray(T[] a)

package toarray;

import java.util.List;
public class TestOne {

    @SuppressWarnings("unchecked")
    public static void main(String[] args) {
        /**
         * 
         * 1、创建一个ArrayList对象，默认创建一个长度是10的数组
         * 
         * 2、add时改变容量size
            public boolean add(E e) {
                ensureCapacityInternal(size + 1);  // Increments modCount!!
                elementData[size++] = e;
                return true;
            }
         * 
         * 
         * 3、toArray()  Arrays拷贝一份数据返回Object[]类型
         public Object[] toArray() {
            return Arrays.copyOf(elementData, size);
         }
         * 
         * 
         4. toArray(T[] a)  传入数组参数，  返回数组类型是参数数组类型
         1）当参数数组长度length小于 ArrayList对象的size，Arrays拷贝一份数据返回
         2）...................................大于................. System.arraycopy拷贝一份数据返回，空余位赋null值
             @SuppressWarnings("unchecked")
            public <T> T[] toArray(T[] a) {
                if (a.length < size)
                    // Make a new array of a's runtime type, but my contents:
                    return (T[]) Arrays.copyOf(elementData, size, a.getClass());
                System.arraycopy(elementData, 0, a, 0, size);
                if (a.length > size)
                    a[size] = null;
                return a;
            }
         */
        
        @SuppressWarnings("rawtypes")
        List list = new ArrayList();
        list.add("1");
        list.add("2");
        list.add("3");
        list.add("4");
        
        String[] arr1 =  (String[]) list.toArray();
        String[] arr2 =  (String[]) list.toArray(new String[6]);
        
        
        for(String str : arr1){  //Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String;
            System.out.println(str); 
        }
        
        for(String str : arr2){
            System.out.println(str); 
        }
        
    }

}