Java.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 + '}';

    }

}