[编程语言][java]Map的几种遍历方式(备忘记录)

 

 

　　集合的一个很重要的操作---遍历，学习了三种遍历方法，三种方法各有优缺点~~

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package cn.tsp2c.liubao;

import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

/**
 *
 * @author Administrator
 */
public class TestMap {

    public static void main(String[] args) {
        Map<String, Student> map = new HashMap<String, Student>();
        Student s1 = new Student("宋江", "1001", 38);
        Student s2 = new Student("卢俊义", "1002", 35);
        Student s3 = new Student("吴用", "1003", 34);
       
        map.put("1001", s1);
        map.put("1002", s2);
        map.put("1003", s3);

        Map<String, Student> subMap = new HashMap<String, Student>();
        subMap.put("1008", new Student("tom", "1008", 12));
        subMap.put("1009", new Student("jerry", "1009", 10));
        map.putAll(subMap);

        work(map);
        workByKeySet(map);
        workByEntry(map);
    }

　　//最常规的一种遍历方法，最常规就是最常用的，虽然不复杂，但很重要，这是我们最熟悉的，就不多说了！！

    public static void work(Map<String, Student> map) {
        Collection<Student> c = map.values();
        Iterator it = c.iterator();
        for (; it.hasNext();) {
            System.out.println(it.next());
        }
    }

　　//利用keyset进行遍历，它的优点在于可以根据你所想要的key值得到你想要的 values，更具灵活性！！

    public static void workByKeySet(Map<String, Student> map) {
        Set<String> key = map.keySet();
        for (Iterator it = key.iterator(); it.hasNext();) {
            String s = (String) it.next();
            System.out.println(map.get(s));
        }
    }

　　//比较复杂的一种遍历在这里，呵呵~~他很暴力哦，它的灵活性太强了，想得到什么就能得到什么~~

    public static void workByEntry(Map<String, Student> map) {
        Set<Map.Entry<String, Student>> set = map.entrySet();
        for (Iterator<Map.Entry<String, Student>> it = set.iterator(); it.hasNext();) {
            Map.Entry<String, Student> entry = (Map.Entry<String, Student>) it.next();
            System.out.println(entry.getKey() + "--->" + entry.getValue());
        }
    }
}

class Student {

    private String name;
    private String id;
    private int age;

    public Student(String name, String id, int age) {
        this.name = name;
        this.id = id;
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" + "name=" + name + "id=" + id + "age=" + age + '}';
    }
}

 

 

摘自：http://www.cnblogs.com/christ/archive/2010/10/30/1865134.html

 

//两种遍历map value的方法

public static void main(String[] args){

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

 map.put("id1", "wang");

 map.put("id2", "sheng");

 //方法一

Set<String> set = map.keySet();

 for (String s:set) {

 System.out.println(s+","+map.get(s));

}

//方法二

Set<Map.Entry<String, String>> entryseSet=map.entrySet();

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

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

 }

}

 

 

 

JDK1.4中

Map map = new HashMap();
Iterator it = map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry entry = (Map.Entry) it.next();
Object key = entry.getKey();
Object value = entry.getValue();
}


JDK1.5中,应用新特性For-Each循环

Map m = new HashMap();
for(Object o : map.keySet()){
    map.get(o);
}


返回的 set 中的每个元素都是一个 Map.Entry 类型。

private Hashtable<String, String> emails = new Hashtable<String, String>();

   //方法一: 用entrySet()
   Iterator it = emails.entrySet().iterator();
   while(it.hasNext()){
    Map.Entry m=(Map.Entry)it.next();
    logger.info("email-" + m.getKey() + ":" + m.getValue());
   }
 
   // 方法二：jdk1.5支持，用entrySet()和For-Each循环()
   for (Map.Entry<String, String> m : emails.entrySet()) {
  
    logger.info("email-" + m.getKey() + ":" + m.getValue());
   }
 
   // 方法三：用keySet()
   Iterator it = emails.keySet().iterator();
   while (it.hasNext()){
    String key;
    key=(String)it.next();
    logger.info("email-" + key + ":" + emails.get(key));
   }

// 方法五：jdk1.5支持，用keySEt()和For-Each循环

for(Object m: emails.keySet()){
    logger.info("email-" + m+ ":" + emails.get(m));
   }

另外 我们可以先把hashMap 转为集合Collection，再迭代输出，不过得到的对象

   Map    aa    =    new    HashMap();  
   aa.put("tmp1",    new    Object());      //追加      替换用同样的函数.  
   aa.remove("temp1");                        //删除  
   for    (Iterator    i    =    aa.values().iterator();    i.hasNext();    )    {  
           Object    temp    =    i.next();  
   }          //遍历  


来个完整的，包含TreeSet的元素内部排序的

public static void main(String[] args) {
   ArrayList<String> list = new ArrayList<String>();
   HashMap<Object,Object> hash = new HashMap<Object,Object>();
   TreeMap<Object,Object> treeMap = new TreeMap<Object,Object>();
   list.add("a");
   list.add("b");
   list.add("c");
 
   hash.put(3, 3);
   hash.put(4, 4);
   hash.put(5, 5);
   hash.put(6, 6);
   hash.put(1, 1);
   hash.put(2, 2);
 
   treeMap.put(1, 1);
   treeMap.put(2, 2);
   treeMap.put(3, 3);
   treeMap.put(4, 4);
   treeMap.put(5, 5);
   treeMap.put(6, 6);
 
   //list遍历
   for(String m: list){
    System.out.println(m);
   }
   // hashmap entrySet() 遍历
   for(Map.Entry<Object,Object> m: hash.entrySet()){
    System.out.println(m.getKey()+"---"+m.getValue());
   }
   //hashmap keySet() 遍历
   for(Object m: hash.keySet()){
    System.out.println(m+"---"+hash.get(m));
   }
   // treemap keySet()遍历
   for(Object m: treeMap.keySet()){
    System.out.println(m+"---"+treeMap.get(m));
   }
}