相信用过vb的朋友都知道,vb中有个collection集合类型,用于保存相关元素值到集合,其实质就是一个列表.Java中对Collection进一步抽象封装,使之成为一个集合的接口,根据此接口,抽象出可重复的List,arrayList列表,也可抽象出不可重复的Set,HashSet列表.下面是使用Collection的范例.希望对大家有帮助.

import java.util.*;
public class test {

 
 public static void main(String[] args) {
  
  // 没有重复的集合列表***********begin**********
  Collection mycoll=new HashSet();
  mycoll.add("China");
  mycoll.add("Canada");
  mycoll.add("Japan");
  mycoll.add("Italy");
  mycoll.add("China");
  System.out.println("size="+mycoll.size());
  for(Iterator it=mycoll.iterator();it.hasNext();)
  {
   System.out.println(it.next());
  }
       //   没有重复的集合列表***********end**********
  System.out.println("******************************");
  //  有重复的集合列表***********begin**********
  Collection lstcoll=new ArrayList();
  lstcoll.add("China");
  lstcoll.add("Canada");
  lstcoll.add("Japan");
  lstcoll.add("Italy");
  lstcoll.add("China");
  System.out.println("size="+lstcoll.size());
  for(Iterator itLst=lstcoll.iterator();itLst.hasNext();)
  {
   System.out.println(itLst.next());
  }
       //    有重复的集合列表***********end********** 
  
 }   

}

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解决方法

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public interface Collection<E> extends Iterable<E> { ... }

public abstract class AbstractCollection<E> implements Collection<E> { ... }

    public boolean add(E e) {   
     throw new UnsupportedOperationException();
    }  
     public boolean addAll(Collection<? extends E> c) {  
      boolean modified = false;
    Iterator<? extends E> e = c.iterator();   
     while (e.hasNext()) {     
       if (add(e.next()))                
         // 调用了上面定义的 add 方法
        modified = true;
    }    return modified;
    }    public abstract Iterator<E> iterator();               
    //未提供具体实现，将实现延迟到具体容器


    public boolean remove(Object o) {
    Iterator<E> e = iterator();    
    if (o==null) {       
     while (e.hasNext()) {       
      if (e.next()==null) {
            e.remove();                 
            //内部使用了迭代器的 remove 方法，故具体容器的迭代器实现密切相关
            return true;
        }
        }
    } else {        
    while (e.hasNext()) {      
      if (o.equals(e.next())) {
            e.remove();           
             return true;
        }
        }
    }    return false;
    }    public boolean removeAll(Collection<?> c) {  
      boolean modified = false;
    Iterator<?> e = iterator();    
    while (e.hasNext()) {     
       if (c.contains(e.next())) {
        e.remove();                       
        //内部使用了迭代器的 remove 方法，故具体容器的迭代器实现密切相关
        modified = true;
        }
    }    return modified;
    }    public boolean retainAll(Collection<?> c) {    
    boolean modified = false;
    Iterator<E> e = iterator();   
     while (e.hasNext()) {        
    if (!c.contains(e.next())) {
        e.remove();                       
        //内部使用了迭代器的 remove 方法，故具体容器的迭代器实现密切相关
        modified = true;
        }
    }    return modified;
    }    public void clear() {
    Iterator<E> e = iterator();    
    while (e.hasNext()) {
        e.next();
        e.remove();                       
        //内部使用了迭代器的 remove 方法，故具体容器的迭代器实现密切相关
    }
    }    public boolean contains(Object o) {
    Iterator<E> e = iterator();    
    if (o==null) {        
    while (e.hasNext())        
    if (e.next()==null)            
    return true;
    } else {        while (e.hasNext())        
    if (o.equals(e.next()))                 
    //内部调用了的 equals方法，故与 equals 方法实现密切相关
            return true;
    }    return false;
    }    public boolean containsAll(Collection<?> c) {
    Iterator<?> e = c.iterator();    
    while (e.hasNext())        
    if (!contains(e.next()))                
    //内部调用了的 contains 方法，故与 contains 方法实现密切相关
        return false;    return true;
    }    //此处省略两个 toArray 方法的实现


    public abstract int size();                   
    //未提供具体实现，将实现延迟到具体容器


    public boolean isEmpty() {    return size() == 0;                      
    //内部调用了的 size 方法，故与 size 方法实现密切相关
    }

public class Unsupported {
    static void test(String msg, List<String> list) {
        System.out.println("--- " + msg + " ---");
        Collection<String> c = list;
        Collection<String> subList = list.subList(1, 8);        
        // Copy of the sublist:
        Collection<String> c2 = new ArrayList<String>(subList);    
            
        try {
            c.retainAll(c2);
        } catch (Exception e) {
            System.out.println("retainAll(): " + e);
        }        try {
            c.removeAll(c2);
        } catch (Exception e) {
            System.out.println("removeAll(): " + e);
        }        try {
            c.clear();
        } catch (Exception e) {
            System.out.println("clear(): " + e);
        }        try {
            c.add("X");
        } catch (Exception e) {
            System.out.println("add(): " + e);
        }        try {
            c.addAll(c2);
        } catch (Exception e) {
            System.out.println("addAll(): " + e);
        }        try {
            c.remove("C");
        } catch (Exception e) {
            System.out.println("remove(): " + e);
        }        // The List.set() method modifies the value but
        // doesn’t change the size of the data structure:
        try {
            list.set(0, "X");
        } catch (Exception e) {
            System.out.println("List.set(): " + e);
        }
    }    public static void main(String[] args) {
        List<String> list = Arrays.asList("A B C D E F G H I J K L".split(" "));

        test("Modifiable Copy", new ArrayList<String>(list)); // 产生新的尺寸可调的
                                                                
                                                                
                                                               // ArrayList

        test("Arrays.asList()", list); // 产生固定尺寸的 ArrayList

        test("unmodifiableList()",
                Collections.unmodifiableList(new ArrayList<String>(list))); // 产生不可修改的列表
    }
} /* Output: 
--- Modifiable Copy --- 

--- Arrays.asList() --- 
retainAll(): java.lang.UnsupportedOperationException 
removeAll(): java.lang.UnsupportedOperationException 
clear(): java.lang.UnsupportedOperationException 
add(): java.lang.UnsupportedOperationException 
addAll(): java.lang.UnsupportedOperationException 
remove(): java.lang.UnsupportedOperationException 

--- unmodifiableList() --- 
retainAll(): java.lang.UnsupportedOperationException 
removeAll(): java.lang.UnsupportedOperationException 
clear(): java.lang.UnsupportedOperationException 
add(): java.lang.UnsupportedOperationException 
addAll(): java.lang.UnsupportedOperationException 
remove(): java.lang.UnsupportedOperationException 
List.set(): java.lang.UnsupportedOperationException

  public static <T> List<T> asList(T... a) {    return new ArrayList<T>(a);
    }

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;
    }    public int size() {       
     return a.length;
    }    public Object[] toArray() {       
     return a.clone();
    }    public <T> T[] toArray(T[] a) {       
     int size = size();        
    if (a.length < size)        
    return Arrays.copyOf(this.a, size,
                     
                     (Class<? extends T[]>) a.getClass());
        System.arraycopy(this.a, 0, a, 0, size);        
        if (a.length > size)
        a[size] = null;        
        return a;
    }    public E get(int index) {        
    return a[index];
    }    public E set(int index, E element) {        
    //该容器支持的操作
        E oldValue = a[index];
        a[index] = element;        
        return oldValue;
    }    public int indexOf(Object o) {        
    if (o==null) {            
    for (int i=0; i<a.length; i++)                
    if (a[i]==null)                    
    return i;
                } else {                    
                for (int i=0; i<a.length; i++)                        
                if (o.equals(a[i]))                            
                return i;
                }        
                return -1;
    }    
    public boolean contains(Object o) 
    {        
    return indexOf(o) != -1;
    }
}

....
其余代码省略
....

// AbstractList 中的方法public boolean add(E e) {
    add(size(), e);    return true;
    }public void add(int index, E element) {    throw new UnsupportedOperationException();
}public boolean addAll(int index, Collection<? extends E> c) {    boolean modified = false;
    Iterator<? extends E> e = c.iterator();    while (e.hasNext()) {
        add(index++, e.next());
        modified = true;
    }    return modified;
}

    //AbstractList 类中方法：
    //该方法继承自 List 接口的：remove(int index) 方法，是 List 特有的方法
    public E remove(int index) {    throw new UnsupportedOperationException();
    }    //AbstractList 类重写了 AbstractCollection 的 clear 方法
     public void clear() {
        removeRange(0, size());
    }   protected void removeRange(int fromIndex, int toIndex) {
        ListIterator<E> it = listIterator(fromIndex);        for (int i=0, n=toIndex-fromIndex; i<n; i++) {
            it.next();
            it.remove();           //直接调用了具体容器的迭代器(由 iterator() 方法返回)的 remove 方法   
        }
    }

    //AbstractCollection 类中方法：
    public boolean remove(Object o) {
    Iterator<E> e = iterator();    if (o==null) {        while (e.hasNext()) {        if (e.next()==null) {
            e.remove();            return true;
        }
        }
    } else {        while (e.hasNext()) {        if (o.equals(e.next())) {
            e.remove();           //直接调用了具体容器的迭代器(由 iterator() 方法返回)的 remove 方法   
            return true;
        }
        }
    }    return false;
    }public boolean removeAll(Collection<?> c) {    boolean modified = false;
    Iterator<?> e = iterator();    while (e.hasNext()) {        if (c.contains(e.next())) {
        e.remove();           //直接调用了具体容器的迭代器(由 iterator() 方法返回)的 remove 方法   
        modified = true;
        }
    }    return modified;
    } public boolean retainAll(Collection<?> c) {    boolean modified = false;
    Iterator<E> e = iterator();    while (e.hasNext()) {        if (!c.contains(e.next())) {
        e.remove();            //直接调用了具体容器的迭代器(由 iterator() 方法返回)的 remove 方法          
        modified = true;
        }
    }    return modified;
    }

   private class Itr implements Iterator<E> {
    /**
     * Index of element to be returned by subsequent call to next.
     */
    int cursor = 0;    /**
     * Index of element returned by most recent call to next or
     * previous.  Reset to -1 if this element is deleted by a call
     * to remove.
     */
    int lastRet = -1;    /**
     * The modCount value that the iterator believes that the backing
     * List should have.  If this expectation is violated, the iterator
     * has detected concurrent modification.
     */
    int expectedModCount = modCount;    
    public boolean hasNext() 
    {            
    return cursor != size();
    }    public E next() 
    {
            checkForComodification();        
            try {
        E next = get(cursor);
        lastRet = cursor++;        
        return next;
        } 
        catch (IndexOutOfBoundsException e) 
        {
        checkForComodification();        
        throw new NoSuchElementException();
        }
    }    public void remove() {        
    if (lastRet == -1)        
    throw new IllegalStateException();
            checkForComodification();        
            try {
        AbstractList.this.remove(lastRet);            
        //直接调用 AbstractList 容器的 remove(int index) 方法，抛出 UnsupportedOperationException      
        if (lastRet < cursor)
            cursor--;
        lastRet = -1;
        expectedModCount = modCount;
        } catch (IndexOutOfBoundsException e) {        
        throw new ConcurrentModificationException();
        }
    }    final void checkForComodification() {        
    if (modCount != expectedModCount)        
    throw new ConcurrentModificationException();
    }
    }