map的三种遍历方法

　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 + '}';
     }
}