Java的Map集合的三种遍历方法

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

1.

package com.myTest.MapText; import java.util.Collection; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Set; public class TestMap { //1. 最常规的一种遍历方法，最常规就是最经常使用的，虽然不复杂，但很重要，这是咱们最熟悉的，就很少说了！！ public static void work(Map<String, Student> map) { Collection<Student> c = map.values(); Iterator<Student> it = c.iterator(); for (; it.hasNext();) { System.out.println(it.next()); } // 当for循环只有一个判断语句的时候，就等同于while循环了 // while(it.hasNext()) // { // System.out.println(it.next()); // } } // 2.利用keyset进行遍历，它的优势在于能够根据你所想要的key值获得你想要的 values，更具灵活性！！ public static void workByKeySet(Map<String, Student> map) { Set<String> key = map.keySet(); Iterator<String> it = key.iterator(); for (; it.hasNext();) { String s = (String) it.next(); System.out.println(map.get(s)); } //用加强型for循环也可 // for(Object o : map.keySet()) // { // System.out.println(map.get(o)); // } } // 3.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，想获得什么就能获得什么~ public static void workByEntry(Map<String, Student> map) { Set<Map.Entry<String, Student>> set = map.entrySet(); Iterator<Map.Entry<String, Student>> it = set.iterator(); for (; it.hasNext();) { Map.Entry<String, Student> entry = (Map.Entry<String, Student>) it.next(); // System.out.println(entry.getKey() + "--->" + entry.getValue()); System.out.println(entry.getValue()); } } 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); } } 

2.

package com.myTest.MapText; public 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 + '}'; } } 

可直接复制代码到Myeclipse工具中运行看结果。