import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;
class People {
private String name;
private int age;
public People(String name, int age) {
super();
this.name = name;
this.age = age;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + age;
result = prime * result + ((name == null) ? 0 : name.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
People other = (People) obj;
if (age != other.age)
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "People [name=" + name + ", age=" + age + "]";
}
}
class HashMapDemo {
public static void main(String[] args) {
HashMap hm = new HashMap();
hm.put(new People("lishuai", 22), 22);
hm.put(new People("liqian", 22), 21);
hm.put(new People("mahongmei", 22), 51);
hm.put(new People("lishuai", 22), 22);
Set s = hm.keySet();
for (Iterator iterator = s.iterator(); iterator.hasNext();) {
Object key = iterator.next();
Object value = hm.get(key);
System.out.println(key + "======" + value);
}
}
}
HashMap的底层也是哈希表,由于是哈希表所以不保证存取有序,也是不同步的。HashMap中的哈希值是作用在key上的。为避免重复元素也就要求复写hashcode,equals方法。