常用List：ArrayList，LinkedList，Vector
ArrayList
ArrayList就是動態數組，是Array的複雜版本，它提供瞭如下一些好處：
1、動態的增加和減少元素
2、實現了Collection和List接口
3、靈活的設置數組的大小
使用方法如下：
ArrayList List = new ArrayList();
for (int i = 0; i < 10; i++) //給數組增加10個Int元素
List.add(i);
List.remove(5);//將第6個元素移除
for (int i = 0; i < 3; i++) //再增加3個元素
List.add(i + 20);
//ArrayList轉數組
Integer[] Array = (Integer[]) List.toArray();注：ArrayList不是同步的
LinkedList
LinkedList其實也就是我們在數據結構中的鏈表，這種數據結構有這樣的特性：
- 分配內存空間不是必須是連續的；
- 插入、刪除操作很快，只要修改前後指針就OK了，時間複雜度爲O(1)；
- 訪問比較慢，必須得從第一個元素開始遍歷，時間複雜度爲O(n)；
在Java中，LinkedList提供了豐富的方法，可以模擬鏈式隊列，鏈式堆棧等數據結構，爲用戶帶來了極大的方便，下面看看這些方法的用法：
add
boolean add(E e)：在鏈表後添加一個元素，如果成功，返回true，否則返回false；
void addFirst(E e)：在鏈表頭部插入一個元素；
addLast(E e)：在鏈表尾部添加一個元素；
void add(int index, E element)：在指定位置插入一個元素。下面是代碼演示：
public class LinkedListMethodsDemo {
public static void main(String[] args) {
LinkedList<String> linkedList = new LinkedList<>();
linkedList.add("first");
linkedList.add("second");
linkedList.add("third");
System.out.println(linkedList);
linkedList.addFirst("addFirst");
System.out.println(linkedList);
linkedList.addLast("addLast");
System.out.println(linkedList);
linkedList.add(2, "addByIndex");
System.out.println(linkedList);
}
}- 輸出：
[first, second, third]
[addFirst, first, second, third]
[addFirst, first, second, third, addLast]
[addFirst, first, addByIndex, second, third, addLast]remove
E remove()；移除鏈表中第一個元素；
boolean remove(Object o)：移除鏈表中指定的元素；
E remove(int index)：移除鏈表中指定位置的元素；
E removeFirst()：移除鏈表中第一個元素，與remove類似；
E removeLast()：移除鏈表中最後一個元素；
boolean removeFirstOccurrence(Object o)：移除鏈表中第一次出現所在位置的元素；
boolean removeLastOccurrence(Object o)：移除鏈表中最後一次出現所在位置的元素；public class LinkedListMethodsDemo {
public static void main(String[] args) {
LinkedList<String> linkedList = new LinkedList<>();
linkedList.add("first");
linkedList.add("second");
linkedList.add("second");
linkedList.add("third");
linkedList.add("four");
linkedList.add("five");
System.out.println(linkedList);
linkedList.remove();
System.out.println("remove: " + linkedList);
linkedList.remove("second");
System.out.println("remove(Object): " + linkedList);
linkedList.remove("six");
System.out.println("remove(Object) not exist: " + linkedList);
linkedList.remove(2);
System.out.println("remove(index): " + linkedList);
linkedList.removeFirst();
System.out.println("removeFirst: " + linkedList);
linkedList.removeLast();
System.out.println("removeLast:" + linkedList);
System.out.println("----------------------------------");
linkedList.clear();
linkedList.add("first");
linkedList.add("second");
linkedList.add("first");
linkedList.add("third");
linkedList.add("first");
linkedList.add("five");
System.out.println(linkedList);
linkedList.removeFirstOccurrence("first");
System.out.println("removeFirstOccurrence: " + linkedList);
linkedList.removeLastOccurrence("first");
System.out.println("removeLastOccurrence: " + linkedList);
}
}輸出：
[first, second, second, third, four, five]
remove: [second, second, third, four, five]
remove(Object): [second, third, four, five]
remove(Object) not exist: [second, third, four, five]
remove(index): [second, third, five]
removeFirst: [third, five]
removeLast:[third]
----------------------------------
[first, second, first, third, first, five]
removeFirstOccurrence: [second, first, third, first, five]
removeLastOccurrence: [second, first, third, five]get
E get(int index)：按照下邊獲取元素；
E getFirst()：獲取第一個元素；
E getLast()：獲取第二個元素；public class LinkedListMethodsDemo {
public static void main(String[] args) {
LinkedList<String> linkedList = new LinkedList<>();
linkedList.add("first");
linkedList.add("second");
linkedList.add("second");
linkedList.add("third");
linkedList.add("four");
linkedList.add("five");
System.out.println(linkedList);
linkedList.get(3);
System.out.println("get(index): " + linkedList.get(3));
linkedList.getFirst();
System.out.println("getFirst: " + linkedList.getFirst());
linkedList.getLast();
System.out.println("getLast: " + linkedList.getLast());
System.out.println(linkedList);
}
}- 輸出：
[first, second, second, third, four, five]
get(index): third
getFirst: first
getLast: five
[first, second, second, third, four, five]- 注意到了，鏈表前後沒有產生變化。
push，pop，poll
void push(E e)：與addFirst一樣，實際上它就是addFirst；
E pop()：與removeFirst一樣，實際上它就是removeFirst；
E poll()：查詢並移除第一個元素；public class LinkedListMethodsDemo {
public static void main(String[] args) {
LinkedList<String> linkedList = new LinkedList<>();
linkedList.push("first");
linkedList.push("second");
linkedList.push("second");
linkedList.push("third");
linkedList.push("four");
linkedList.push("five");
System.out.println("linkedList: " + linkedList);
System.out.println("pop: " + linkedList.pop());
System.out.println("after pop: " + linkedList);
System.out.println("poll: " + linkedList.poll());
System.out.println("after poll: " + linkedList);
}
}- 輸出：
linkedList: [five, four, third, second, second, first]
pop: five
after pop: [four, third, second, second, first]
poll: four
after poll: [third, second, second, first]- 通過代碼示例可以看出：push，pop的操作已經很接近stack的操作了。
如果鏈表爲空的時候，看看poll與pop是啥區別：
public class LinkedListMethodsDemo {
public static void main(String[] args) {
LinkedList<String> linkedList = new LinkedList<>();
System.out.println("poll: " + linkedList.poll());
System.out.println("pop: " + linkedList.pop());
}
}- 輸出：
poll: null
Exception in thread "main" java.util.NoSuchElementException
at java.util.LinkedList.removeFirst(LinkedList.java:270)
at java.util.LinkedList.pop(LinkedList.java:801)
at org.ks.algorithm.LinkedListMethodsDemo.main(LinkedListMethodsDemo.java:13)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)- 可以看出poll返回null，而pop則產生異常。
peek
E peek()：獲取第一個元素，但是不移除；
E peekFirst()：獲取第一個元素，但是不移除；
E peekLast()：獲取最後一個元素，但是不移除；public class LinkedListMethodsDemo {
public static void main(String[] args) {
LinkedList<String> linkedList = new LinkedList<>();
linkedList.push("first");
linkedList.push("second");
linkedList.push("second");
linkedList.push("third");
linkedList.push("four");
linkedList.push("five");
System.out.println("linkedList: " + linkedList);
System.out.println("peek: " + linkedList.peek());
System.out.println("peekFirst: " + linkedList.peekFirst());
System.out.println("peekLast: " + linkedList.peekLast());
System.out.println("linkedList: " + linkedList);
}
}- 輸出：
linkedList: [five, four, third, second, second, first]
peek: five
peekFirst: five
peekLast: first
linkedList: [five, four, third, second, second, first]- 如果沒找到對應的元素，統統輸出null：
public class LinkedListMethodsDemo {
public static void main(String[] args) {
LinkedList<String> linkedList = new LinkedList<>();
System.out.println("linkedList: " + linkedList);
System.out.println("peek: " + linkedList.peek());
System.out.println("peekFirst: " + linkedList.peekFirst());
System.out.println("peekLast: " + linkedList.peekLast());
}
}- 輸出：
linkedList: []
peek: null
peekFirst: null
peekLast: nulloffer
boolean offer(E e)：在鏈表尾部插入一個元素；
boolean offerFirst(E e)：與addFirst一樣，實際上它就是addFirst；boolean offerLast(E e)：與addLast一樣，實際上它就是addLast；
public class LinkedListMethodsDemo {
public static void main(String[] args) {
LinkedList<String> linkedList = new LinkedList<>();
linkedList.push("first");
linkedList.push("second");
linkedList.push("second");
linkedList.push("third");
linkedList.push("four");
linkedList.push("five");
System.out.println("linkedList: " + linkedList);
linkedList.offer("six");
System.out.println("linkedList: " + linkedList);
linkedList.offerFirst("zero");
System.out.println("linkedList: " + linkedList);
linkedList.offerLast("seven");
System.out.println("linkedList: " + linkedList);
}
}- 輸出：
linkedList: [five, four, third, second, second, first]
linkedList: [five, four, third, second, second, first, six]
linkedList: [zero, five, four, third, second, second, first, six]
linkedList: [zero, five, four, third, second, second, first, six, seven]- 其他
LinkedList中常用的方法基本都列出來了，當然還有一些其他的例子，這裏就一起演示了：
public class LinkedListMethodsDemo {
public static void main(String[] args) {
LinkedList<String> linkedList = new LinkedList<>();
linkedList.push("first");
linkedList.push("second");
linkedList.push("second");
linkedList.push("third");
linkedList.push("four");
linkedList.push("five");
System.out.println("linkedList: " + linkedList);
System.out.println("linkedList.contains(\"second\"): " + linkedList.contains("second"));
System.out.println("linkedList.contains(\"six\"): " + linkedList.contains("six"));
System.out.println("linkedList.element(): " + linkedList.element());
System.out.println("linkedList: " + linkedList);
System.out.println("linkedList.set(3, \"set\"): " + linkedList.set(3, "set"));
System.out.println("linkedList: " + linkedList);
System.out.println("linkedList.subList(2,4): " + linkedList.subList(2,4));
System.out.println("linkedList: " + linkedList);
}
}- 輸出：
linkedList: [five, four, third, second, second, first]
linkedList.contains("second"): true
linkedList.contains("six"): false
linkedList.element(): five
linkedList: [five, four, third, second, second, first]
linkedList.set(3, "set"): second
linkedList: [five, four, third, set, second, first]
linkedList.subList(2,4): [third, set]
linkedList: [five, four, third, set, second, first]- 從輸出可以看出，除了set改變原linkedlist，其他幾個方法都不改變原鏈表。
Vector
Vector非常類似ArrayList，但是Vector是同步的。由Vector創建的Iterator，雖然和ArrayList創建的 Iterator是同一接口，但是，因爲Vector是同步的，當一個Iterator被創建而且正在被使用，另一個線程改變了Vector的狀態（例如，添加或刪除了一些元素），這時調用Iterator的方法時將拋出ConcurrentModificationException，因此必須捕獲該異常。
