我很确定我没有正确创建构造函数。我正在使用Vectors（不是选择）的事实让我很困惑。我做对了吗？ Vector有深度复制方法吗？
感谢您的帮助。
import java.util.Vector;
import java.util.Iterator;
public class ListVectorBased<E> implements ListInterface<E>, Iterable<E> {
/** array on which the list is based */
private Vector<E> items;
/** default Constructor */
public ListVectorBased() {
}
/** constructor with the first item: constructs a list with the
* specified item as single element of this list
* @param item first element of the list
*/
public ListVectorBased(E elt) {
items.add(1, elt);
}
/** copy constructor: create a duplicate of the specified list
* @param list to be copied
*/
public ListVectorBased(Vector<E> items) {
this.items = items;
}
/** Tests if this list has no elements.
* @return <code>true</codeif this list has no elements;
* <code>false</codeotherwise.
*/
public boolean isEmpty() {
return items.isEmpty();
} // end isEmpty
/**
* Returns the number of elements in this list.
* @return the number of elements in this list.
*/
public int size() {
return items.size();
} // end size
/**
* Remove all the elements in this list.
*/
public void removeAll() {
items.removeAllElements();
} // end removeAll
/**
* 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 item element to be inserted.
* @throws IndexOutOfBoundsException - if index is out of range
* (index < 0 || index size()).
*/
public void add(int index, E item) throws ListIndexOutOfBoundsException {
if (index >= 1 && index <= items.size()+1) {
items.add(index-1,item);
} else { // index out of range
throw new ListIndexOutOfBoundsException("ListIndexOutOfBoundsException on add");
} // end if
} //end add
/**
* appends the specified element to the end of this list.
* @param elt element to be added at the end of the list
*/
public void append(E elt) {
add (items.size()+1, elt);
}
/**
* Returns the element at the specified position in this list.
* @param index index of element to return.
* @return the element at the specified position in this list.
* @throws IndexOutOfBoundsException - if index is out of range
* (index < 0 || index size()).
*/
public E get(int index) throws ListIndexOutOfBoundsException {
if (index >= 1 && index <= items.size()) {
return items.get(index-1);
} else { // index out of range
throw new ListIndexOutOfBoundsException(
"ListIndexOutOfBoundsException on get");
} // end if
} // end get
/**
* Removes the element at the specified position in this
* list. Shifts any subsequent elements to the left (subtracts one
* from their indices).
* @param index the index of the element to remove
* @throws IndexOutOfBoundsException - if index is out of range
* (index < 0 || index size()).
*/
public void remove(int index) throws ListIndexOutOfBoundsException {
if (index >= 1 && index <= items.size()) {
// delete item by shifting all items at
// positions index toward the beginning of the list
// (no shift if index == size)
items.remove(index-1);
} else { // index out of range
throw new ListIndexOutOfBoundsException(
"ListIndexOutOfBoundsException on remove");
} // end if
} //end remove
/** delete
* delete the the specified element in this list if exists. Shifts
* any subsequent elements to the left (subtracts one from their
* indices).
* @param elt the element, if it exists, to delete
*/
public void delete (E elt) {
if (items.contains(elt)) {
items.remove(elt);
}
}
/** contains
* Looks for the index of the specified element in this list. If
* the element is not present, the method returns <code>-1</code>
* @param elt the element which index is looked for.
* @return either the index of the location in the list where the
* argument is present or <code>-1</codeif the argument is not
* contained in the list.
*/
public int contains(E elt) {
for (int idx = 1; idx <= items.size(); idx++) {
if (items.get(idx).equals(elt))
return idx;
else
return -1;
} // end for
} //end contains
/** display
* Prints all the elements in this list on the console in sequence
*/
public void display() {
for (int idx = 1; idx <= items.size(); idx++) {
System.out.print(items.get(idx));
} //end for
} //end display
/** method to make the class iterable */
public Iterator<E> iterator(){
return items.iterator();
}
} // end ListVectorBased
答案 0 :(得分：0)
我看到的最大问题是某些构造函数初始化items而其他构造函数不初始化，但其他代码假定项目为非null。我的建议是创建项目final，始终创建一个新的向量，然后根据需要将通过构造函数传入的任何项目复制到新的私有向量。
（注意，目前，在你将vector作为参数的构造函数中，你只是复制对向量的引用，这意味着，你不知道，一些外部代码可能会搞乱你的“私有”任何时候的矢量。那种方式就是疯狂......）
即：
/** array on which the list is based */
private final Vector<E> items=new Vector<E>();
/** default Constructor */
public ListVectorBased() {
}
/** constructor with the first item: constructs a list with the
* specified item as single element of this list
* @param item first element of the list
*/
public ListVectorBased(E elt) {
items.add(elt);
}
/** copy constructor: create a duplicate of the specified list
* @param list to be copied
*/
public ListVectorBased(Vector<E> items) {
this.items.addAll(items);
}