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List（接口） 顺序是List最重要的特性它可保证元素按照规定的顺序排列List为Collection添加了大量方法以便我们在List中部插入和删除元素（只推荐对LinkedList这样做）List也会生成一个ListIterator（列表反复器）利用它可在一个列表里朝两个方向遍历同时插入和删除位于列表中部的元素（同样地只建议对LinkedList这样做） ArrayList＊ 由一个数组后推得到的List作为一个常规用途的对象容器使用用于替换原先的Vector允许我们快速访问元素但在从列表中部插入和删除元素时速度却嫌稍慢一般只应该用ListIterator对一个ArrayList进行向前和向后遍历不要用它删除和插入元素与LinkedList相比它的效率要低许多 LinkedList 提供优化的顺序访问性能同时可以高效率地在列表中部进行插入和删除操作但在进行随机访问时速度却相当慢此时应换用ArrayList也提供了addFirst()addLast()getFirst()getLast()removeFirst()以及removeLast()（未在任何接口或基础类中定义）以便将其作为一个规格队列以及一个双向队列使用 下面这个例子中的方法每个都覆盖了一组不同的行为每个列表都能做的事情（basicTest()）通过一个反复器遍历（iterMotion()）用一个反复器改变某些东西（iterManipulation()）体验列表处理的效果（testVisual()）以及只有LinkedList才能做的事情等 //: Listjava // Things you can do with Lists package cnewcollections; import javautil*; public class List { // Wrap Collectionfill() for convenience: public static List fill(List a) { return (List)Collectionfill(a); } // You can use an Iterator just as with a // Collection but you can also use random // access with get(): public static void print(List a) { for(int i = ; i < a.size(); i++) System.out.print(a.get(i) + " "); System.out.println(); } static boolean b; static Object o; static int i; static Iterator it; static ListIterator lit; public static void basicTest(List a) { a.add(1, "x"); // Add at location 1 a.add("x"); // Add at end // Add a collection: a.addAll(fill(new ArrayList())); // Add a collection starting at location 3: a.addAll(3, fill(new ArrayList())); b = ntains("1"); // Is it in there? // Is the entire collection in there? b = ntainsAll(fill(new ArrayList())); // Lists allow random access, which is cheap // for ArrayList, expensive for LinkedList: o = a.get(1); // Get object at location 1 i = a.indexOf("1"); // Tell index of object // indexOf, starting search at location 2: i = a.indexOf("1", 2); b = a.isEmpty(); // Any elements inside? it = erator(); // Ordinary Iterator lit = a.listIterator(); // ListIterator lit = a.listIterator(3); // Start at loc 3 i = a.lastIndexOf("1"); // Last match i = a.lastIndexOf("1", 2); // ...after loc 2 a.remove(1); // Remove location 1 a.remove("3"); // Remove this object a.set(1, "y"); // Set location 1 to "y" // Keep everything that's in the argument // (the intersection of the two sets): a.retainAll(fill(new ArrayList())); // Remove elements in this range: a.removeRange(0, 2); // Remove everything that's in the argument: a.removeAll(fill(new ArrayList())); i = a.size(); // How big is it? a.clear(); // Remove all elements } public static void iterMotion(List a) { ListIterator it = a.listIterator(); b = it.hasNext(); b = it.hasPrevious(); o = it.next(); i = it.nextIndex(); o = it.previous(); i = it.previousIndex(); } public static void iterManipulation(List a) { ListIterator it = a.listIterator(); it.add("47"); // Must move to an element after add(): it.next(); // Remove the element that was just produced: it.remove(); // Must move to an element after remove(): it.next(); // Change the element that was just produced: it.set("47"); } public static void testVisual(List a) { print(a); List b = new ArrayList(); fill(b); System.out.print("b = "); print(b); a.addAll(b); a.addAll(fill(new ArrayList())); print(a); // Shrink the list by removing all the // elements beyond the first 1/2 of the list System.out.println(a.size()); System.out.println(a.size()/2); a.removeRange(a.size()/2, a.size()/2 + 2); print(a); // Insert, remove, and replace elements // using a ListIterator: ListIterator x = a.listIterator(a.size()/2); x.add("one"); print(a); System.out.println(x.next()); x.remove(); System.out.println(x.next()); x.set("47"); print(a); // Traverse the list backwards: x = a.listIterator(a.size()); while(x.hasPrevious()) System.out.print(x.previous() + " "); System.out.println(); System.out.println("testVisual finished"); } // There are some things that only // LinkedLists can do: public static void testLinkedList() { LinkedList ll = new LinkedList(); Collection1.fill(ll, 5); print(ll); // Treat it like a stack, pushing: ll.addFirst("one"); ll.addFirst("two"); print(ll); // Like "peeking" at the top of a stack: System.out.println(ll.getFirst()); // Like popping a stack: System.out.println(ll.removeFirst()); System.out.println(ll.removeFirst()); // Treat it like a queue, pulling elements // off the tail end: System.out.println(ll.removeLast()); // With the above operations, it's a dequeue! print(ll); } public static void main(String args[]) { // Make and fill a new list each time: basicTest(fill(new LinkedList())); basicTest(fill(new ArrayList())); iterMotion(fill(new LinkedList())); iterMotion(fill(new ArrayList())); iterManipulation(fill(new LinkedList())); iterManipulation(fill(new ArrayList())); testVisual(fill(new LinkedList())); testLinkedList(); } } ///:~ 在basicTest()和iterMotiion()中，只是简单地发出调用，以便揭示出正确的语法。TW.WInGWit.CoM而且尽管捕获了返回值，但是并未使用它。在某些情况下，之所以不捕获返回值，是由于它们没有什么特别的用处。在正式使用它们前，应仔细研究一下自己的联机文档，掌握这些方法完整、正确的用法。 |
