import java.util.ArrayList; import java.util.Arrays; import java.util.HashSet; import java.util.List; public class ArraysAsListDemo { public static void main(String[] args) { List<String> source1 = new ArrayList<String>(Arrays.asList("1", "2", "3")); ArrayList<String> source2 = new ArrayList<String>(Arrays.asList("5", "62", "3")); source2.removeAll(source1); System.out.println(source2); // Arrays.asList("1", "2", "3").remove("1");//会报错。因为Arrays$ArrayList中没有实现List接口中的remove方法 System.out.println(source1.containsAll(source2)); HashSet<String> total = new HashSet<String>(); total.addAll(source1); total.addAll(source2); System.out.println(total.size() > (source1.size() + source2.size())); System.out.println(total.size() < (source1.size() + source2.size())); } }
// Misc /** * Returns a fixed-size list backed by the specified array. (Changes to * the returned list "write through" to the array.) This method acts * as bridge between array-based and collection-based APIs, in * combination with {@link Collection#toArray}. The returned list is * serializable and implements {@link RandomAccess}. * * <p>This method also provides a convenient way to create a fixed-size * list initialized to contain several elements: * <pre> * List<String> stooges = Arrays.asList("Larry", "Moe", "Curly"); * </pre> * * @param a the array by which the list will be backed * @return a list view of the specified array */ public static <T> List<T> asList(T... a) { return new ArrayList<T>(a); } /** * @serial include */ private static class ArrayList<E> extends AbstractList<E> implements RandomAccess, java.io.Serializable { private static final long serialVersionUID = -2764017481108945198L; private final E[] a; ArrayList(E[] array) { if (array==null) throw new NullPointerException(); a = array; }
说明：
在jdk文档中对RandomAccess接口的定义如下:
public interface RandomAccess
List 实现所使用的标记接口，用来表明其支持快速（通常是固定时间）随机访问。
此接口的主要目的是允许一般的算法更改其行为，从而在将其应用到随机或连续访问列表时能提供良好的性能。
将操作随机访问列表的最佳算法（如 ArrayList ）应用到连续访问列表（如 LinkedList ）时，可产生二次项的行为。
如果将某个算法应用到连续访问列表，那么在应用可能提供较差性能的算法前，鼓励使用一般的列表算法检查给定列表是否为此接口的一个 instanceof ，
如果需要保证可接受的性能，还可以更改其行为。现在已经认识到，随机和连续访问之间的区别通常是模糊的。
例如，如果列表很大时，某些 List 实现提供渐进的线性访问时间，但实际上是固定的访问时间。这样的 List 实现通常应该实现此接口。
强调:
JDK中推荐的是对List集合尽量要实现RandomAccess接口
如果集合类是RandomAccess的实现，则尽量用for(int i = 0; i < size; i++) 来遍历而不要用Iterator迭代器来遍历，在效率上要差一些。
反过来，如果List是Sequence List，则最好用迭代器来进行迭代。
package java.util;
public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable { private static final long serialVersionUID = 8683452581122892189L; /** * The array buffer into which the elements of the ArrayList are stored. * The capacity of the ArrayList is the length of this array buffer. */ private transient Object[] elementData; /** * The size of the ArrayList (the number of elements it contains). * * @serial */ private int size;
public interface List<E> extends Collection<E> { // Query Operations /** * Returns the number of elements in this list. If this list contains * more than <tt>Integer.MAX_VALUE</tt> elements, returns * <tt>Integer.MAX_VALUE</tt>. * * @return the number of elements in this list */ int size(); /** * Returns <tt>true</tt> if this list contains no elements. * * @return <tt>true</tt> if this list contains no elements */ boolean isEmpty();
* @author Josh Bloch * @author Neal Gafter * @version 1.55, 04/21/06 * @see Set * @see List * @see Map * @see SortedSet * @see SortedMap * @see HashSet * @see TreeSet * @see ArrayList * @see LinkedList * @see Vector * @see Collections * @see Arrays * @see AbstractCollection * @since 1.2 */ public interface Collection<E> extends Iterable<E> { // Query Operations /** * Returns the number of elements in this collection. If this collection * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns * <tt>Integer.MAX_VALUE</tt>. * * @return the number of elements in this collection */ int size(); /** * Returns <tt>true</tt> if this collection contains no elements. * * @return <tt>true</tt> if this collection contains no elements */ boolean isEmpty();