java中关于Map的三种遍历方法详解

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 + '}';
    }
}