Java的HashMap，HashSet

HashMap=数组（桶）+链表，同C++中STL中的hashmap

1/遍历方式

第一种:
　　Map map = new HashMap();
　　Iterator iter = map.entrySet().iterator();
　　while (iter.hasNext()) {
　　Map.Entry entry = (Map.Entry) iter.next();
　　Object key = entry.getKey();
　　Object val = entry.getValue();
　　}
　　效率高

第二种:
　　Map map = new HashMap();
　　Iterator iter = map.keySet().iterator();
　　while (iter.hasNext()) {
　　Object key = iter.next();
　　Object val = map.get(key);
　　}
　　效率低

HashSet  插入不重复的元素

 public class myclass
{  
  public static void main(String[] args)
  {
   HashSet hs=new HashSet();
   hs.add(new Emp("1","zhangsan",45));
   hs.add(new Emp("2","lisi",90));
   hs.add(new Emp("3","wangwu",67.5f));
   hs.add(new Emp("6","zhangsanyi",78.8f));
   Iterator it=hs.iterator();
   while(it.hasNext())
   { System.out.println(it.next());
   }
  }

} 

 class Emp {    
   private String name;    
   private float sal;    
   private String num;           
   public Emp(String num,String name,float sal)    
      {  this.num=num;   
         this.name=name;  
         this.sal=sal;    
      }                 
   public String getName() {  return name;   }      
   public void setName(String name) {   this.name = name; }   
   public float getSal() {  return sal;  }       
   public void setSal(float sal) {   this.sal = sal;   }       
   public String getNum() {   return num;  }       
   public void setNum(String num) {  this.num = num;  }
    public String toString() 
      { 
           return getName() + " - " + getSal() +" - "+getNum(); 
     }
    public int hashcode()
    {
     return (int)sal * name.hashCode();
    }
    public boolean equals(Emp s)
    {
     return sal == s.sal && name.equals(s.name) &&  num.equals(s.num);
     }
 }

输出：

lisi - 90.0 - 2
zhangsan - 45.0 - 1
wangwu - 67.5 - 3
zhangsanyi - 78.8 - 6