java循环遍历数组，List，Map

1  遍历数组

     ①循环遍历数组有2中方式，遍历一维数组只需要一个for循环，遍历二维数组需要2个for循环。

     publicstaticvoidmain(String[] args) {

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

           for ( inti = 0; i < arr.length;i++) {

                for ( intj = 0; j < arr[i].length;j++) {

                     System.out.print(arr[i][j]);

                }

                System.out.println();

           }

     }

     ②for-each语句遍历

     publicstaticvoidmain(String[] args) {

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

           for (String[] i : arr) {//外层遍历得到一维数组

                for (String j : i) {//内层遍历得到数组元素

                     System.out.print(j);

                }

                System.out.println();

           }

     }

2  遍历List

     ①for循环：

     publicstaticvoidmain(String[] args) {

           List<String>list=new ArrayList<String>();

           list.add("a");

           list.add("b");

           list.add("c");

           for(int i=0; i< list.size(); i++){

                System.out.println(list.get(i));

           }

     }

     ②for-each语句遍历

           for(Stringtmp : list){

                System.out.println(tmp);

           }

     ③迭代器遍历

           Iterator<String>tmp=list.iterator();

           while(tmp.hasNext()){

                System.out.println(tmp.next());

           }

           ------------------------------------------------------------

           for(Iterator<String>tmp=list.iterator();tmp.hasNext();){

                System.out.println(tmp.next());

           }

3  遍历Map     

     ①键和值都需要（for-each循环）

     publicstaticvoidmain(String[] args) {

           Map<String,String>map=new HashMap<String, String>();

           map.put("a","b");

           map.put("c","d");

           map.put("e","f");

           for(Map.Entry<String,String>entry:map.entrySet()){

                System.out.println("key="+entry.getKey()+",value="+entry.getValue());

           }

     }

     ②只需要键或者值（可以通过keySet或values来实现遍历，而不是entrySet）

           for(Stringkey:map.keySet()){

                System.out.println("key="+key);

           }

               -------------------------------------------------------------------

           for(Stringvalue:map.values()){

                System.out.println("value="+value);

           }

     ③Itreator遍历

           Iterator<Map.Entry<String, String>>tmp=map.entrySet().iterator();

           while(tmp.hasNext()){//使用泛型

                Map.Entry<String, String>tm=tmp.next();

                System.out.println("key="+tm.getKey()+",value="+tm.getValue());

           }

               -----------------------------------------------------------

           Iterator tmp=map.entrySet().iterator();

           while(tmp.hasNext()){//不使用泛型

                Map.Entry tm= ( Map.Entry) tmp .next();

                Stringkey = (String) tm.getKey();

                Stringvalue = (String) tm.getValue();

                System.out.println("Key = " + key + ", Value = "+ value);

           }

           你也可以在keySet和values上应用同样的方法

     ④通过键找值遍历（效率低）

           for(Stringkey:map.keySet()){

                Stringvalue=map.get(key);

                System.out.println("key="+key+",value="+value);

           }