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Detailed explanation of the three traversal methods of Map in Java

高洛峰
Release: 2017-01-22 16:17:15
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Three traversal methods of map!
A very important operation of collections---traversal. I have learned three traversal methods. Each of the three methods has its own advantages and disadvantages~~

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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 + &#39;}&#39;;
    }
}
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