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~~

复制代码 代码如下:

/*

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* and open the template in the editor.

*/

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 + '}';

}

}