java集合之Map_keySet

java集合之Map_keySet_entrySet

keySet()的使用:该方法返回的是一个key对象的Set<E>集合，通过该set集合的对象调用iterator方法返回一个迭代器，通过该迭代器可访问到set集合里面的key

　　　　　　　　再调用HashMap集合里面的get(Object key);方法即可得到key值

package collection;

import java.util.*;

public class MyMap2 {

    public static void main(String[] args) {
        Map<Person2,Contact2> m1 = new HashMap<Person2,Contact2>();
        Person2 p1 = new Person2(123,"张三");
        Person2 p2 = new Person2(12,"李四");
        Contact2 c1 = new Contact2(13199898778l,"河南");
        Contact2 c2 = new Contact2(15999898778l,"北京");
        m1.put(p1, c1);
        m1.put(p2, c2);
        Set<Person2> set1  = m1.keySet(); 
        Iterator<Person2> it1 = set1.iterator();
        while(it1.hasNext()){
            Person2    key = it1.next();
            Contact2 value = m1.get(key);
            System.out.println("key键："+key);
            System.out.println("value值："+value);
        }
        
    }

}
class Person2 {
    int id ;
    String name;
    public Person2(int id, String name) {
        //super();
        this.id = id;
        this.name = name;
    }
    @Override
    public String toString() {
        return "Person2 [id=" + id + ", name=" + name + "]";
    }
    
}
class Contact2{
    long telephont;
    String address;
    public Contact2(long telephont, String address) {
        //super();
        this.telephont = telephont;
        this.address = address;
    }
    @Override
    public String toString() {
        return "Contact2 [telephont=" + telephont + ", address=" + address + "]";
    }
}

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key键：Person2 [id=123, name=张三]
value值：Contact2 [telephont=13199898778, address=河南]
key键：Person2 [id=12, name=李四]
value值：Contact2 [telephont=15999898778, address=北京]

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entrySet()的使用：返回此映射中包含的映射关系的set试图——jdk1.6

　　　　　　　　　　理解为返回Map.Entry<K,V>类的一个对象，K，V都是Map键值对中对应的属性，在Map.Entry中K又是该Map.Entry的一个属性，V也是Map.Entry的一个

　　　　　　　　　　属性.通过返回的对象调用迭代器，才能访问到Map.Entry<K,V>里面的元素。

　　代码如下：

 1 package collection;
 2 
 3 import java.util.*;
 4 
 5 
 6 public class MyMap_entrySet2 {
 7 
 8     public static void main(String[] args) {
 9         Map  m1 = new TreeMap(); 
10         Person5 p1 = new Person5(1332,"xiaoming");
11         Person5 p2 = new Person5(8332,"ahangsan");
12         Contact5 c1 = new Contact5(13172673363l,"广州");
13         Contact5 c2 = new Contact5(15172673363l,"杭州");
14         m1.put(p1, c1);
15         m1.put(p2, c2);
16         //System.out.println(m1);
17         Set<Map.Entry<Person5, Contact5>> map_entry = m1.entrySet();//获取Map.Entry的对象
18         Iterator<Map.Entry<Person5, Contact5>> it = map_entry.iterator();//获取迭代器
19         while(it.hasNext()){
20         Person5 p =it.next().getKey();//通过迭代器访问Map.Entry里面的元素
21         Contact5 c =(Contact5) m1.get(p);//key得到他的value
22             System.out.println(p);
23             System.out.println(c);
24         }
25     }
26 
27 }
28 class Person5 implements Comparable {
29     int id ;
30     String name;
31     public Person5(int id, String name) {
32         //super();
33         this.id = id;
34         this.name = name;
35     }
36     public int compareTo(Object obj){
37         Person5 p4 = (Person5)obj ;
38             return this.name.compareTo(p4.name);//根据返回值，按照二叉树结构，进行存储。
39     }                                            //P84《数据结构与算法分析java语言描述》佛罗里达国际大学    
40     @Override
41     public String toString() {
42         return "Person5 [id=" + id + ", name=" + name + "]";
43     }
44     
45 }
46 class Contact5{
47     long telephont;
48     String address;
49     public Contact5(long telephont, String address) {
50         //super();
51         this.telephont = telephont;
52         this.address = address;
53     }
54     @Override
55     public String toString() {
56         return "Contact5 [telephont=" + telephont + ", address=" + address + "]";
57     }
58     
59 }

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