HashMap

import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;
import java.util.Map.Entry;


public class HashMapTest {

/**
*Map集合需要保证键的唯一性
*HashMap是通过HashSet原理保证键的一列不重复，所以存入键的对象需要正确重写hashCode和equals方法
*/
public static void main(String[] args) {
HashMap<Person, String> hm = new HashMap<Person, String>();
hm.put(new Person("zhangsan", 19), "zhangsan");
hm.put(new Person("wangwu", 21), "wangwu");
hm.put(new Person("lisi", 32), "lisi");
hm.put(new Person("zhangsan", 19), "zhangsan");
hm.put(new Person("zhangsan", 21), "zhangsan");
hm.put(new Person("wangwu", 21), "wangwu");

System.out.println(hm.size());

//遍历Map集合，两种方式，取键再取值，直接取键值对
//1.调用keySet方法取所有的键组成的Set集合，遍历，根据每个键调用get方法取对应的值
Set<Person> keys = hm.keySet(); //获得所有key
Iterator<Person> iter = keys.iterator();
while(iter.hasNext()) {
Person key = iter.next();
//根据键取值
String value = hm.get(key);
System.out.println(key + "---" + value);
}

//2.调用entrySet方法取所有的键值对组成的set集合，遍历，再调用getKey取键，调用getValue取值
Set<Entry<Person, String>> entrys = hm.entrySet();
for(Entry<Person, String> entry : entrys) {
Person key = entry.getKey();
String value = entry.getValue();
System.out.println(key + "~~~" + value);
}
}

}