Java 中数组声明后不可修改 –跟C一样 ，C中往往会增加定义HASHTABLE,链表等结构来实现动态的数组

但在java中,已经有现成的,称为集合

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Collection (interface,有迭代器)

├List (interface)

│├LinkedList (class)

│├ArrayList (class)

│└Vector (class,同步)

│　└Stack (class，栈)

├Set (interface,不重复元素)

│├SortedSet (interface)

│├AbstractSet (abstract class)

││├HashSet(class 类似set,基于hashmap)

││├TreeSet (class类似set, 带自动排序,基于Treemap)

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Map(interface,有迭代器,key,value)
├Hashtable
├HashMap (同步)

|- TreeMap (带自动排序)
└WeakHashMap (自动GC的hashmap)

Map.Entry Map 的每个子元素接口，所有map均可使用

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所有集合均实现迭代器

//迭代器循环

Hashtable<String, String> ffh= new Hashtable<String,String>();

ffh.put("a", "b");

ffh.put("u", "fff");

Iterator<String> ddf=ffh.keySet().iterator();

while (ddf.hasNext()) {

????String k=ddf.next();

????System.out.print("Key"+k);

????String v=ffh.get(k);

????System.out.print("Vlau"+v);

}

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//for

Vector<String> ddfe= new Vector<String>();

ddfe.add("fasdfa");

ddfe.add("");

for(String fefe:ddfe){

????System.out.print(fefe);

}

//for

HashMap<String, String> hm= new HashMap<String,String>();

hm.put("ddd","ccc");

for(Map.Entry<String, String> temp:hm.entrySet()){

????System.out.print(temp.getKey());

????System.out.print(temp.getValue());

}

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//for

TreeMap<String,String> ddff=new TreeMap<String,String>();

ddff.put("c", "d");

ddff.put("a", "b");

for(Map.Entry<String, String> temp:ddff.entrySet()){

????System.out.print(temp.getKey());

????System.out.print(temp.getValue());

}

//for

Vector<String> tset= new Vector<String>();

tset.add("a");

tset.add("b");

for(String temp:tset){

????System.out.print(temp);

}

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//将数组转为集合，不能修改元素

String [] c={"a","b"};

List<String> temp=Arrays.asList(c);

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