hasSet,TreeSet,ArrayList,LinkedList,Vector,HashMap,HashTable,TreeMap利用Iterator进行输出-白红宇

hasSet,TreeSet,ArrayList,LinkedList,Vector,HashMap,HashTable,TreeMap利用Iterator进行输出

阅读量：6240 次

发布时间：2019-06-22

本文共 9573 字，大约阅读时间需要 31 分钟。

基础类，没有重写hashCode()和equals()方法：

package niukewang;import java.util.Objects;public class setClass {    String a;    String b;    public setClass(String a, String b)    {        this.a=a;        this.b=b;        }    }

测试类：

package niukewang;import java.util.ArrayList;import java.util.HashMap;import java.util.HashSet;import java.util.Hashtable;import java.util.Iterator;import java.util.LinkedList;import java.util.List;import java.util.Map;import java.util.Map.Entry;import java.util.Set;import java.util.TreeMap;import java.util.TreeSet;import java.util.Vector;public class test1 {    public static void main(String args[])     {         setClass s1=new setClass("http://www.yjbys.com/", "");        setClass s2=new setClass("http://www.yjbys.com1/", "");        setClass s3=new setClass("http://www.yjbys.com2/", "");        setClass s4=new setClass("http://www.yjbys.com2/", "");                //hasSet        System.out.println("hasSet......");        Set
     
       set=new HashSet
      
       ();        set.add(s1);        set.add(s2);        set.add(s3);        set.add(s4);        Iterator it= set.iterator();        while(it.hasNext())        {            setClass ob=(setClass)it.next();            System.out.println(ob.a);        }        /*        //TreeSet        System.out.println("\nTreeSet........");        Set
       
         tree=new TreeSet
        
         ();        tree.add(s1);        tree.add(s2);        tree.add(s3);        tree.add(s4);        Iterator treeit=tree.iterator();        while(treeit.hasNext())        {            setClass ob=(setClass) treeit.next();            System.out.println(ob.a);        }        */        //TreeMap/*        System.out.println("\nTreeMap.........");        Map
         
           treemap=new TreeMap
          
           (); treemap.put(s1, "TreeMap one"); treemap.put(s2, "TreeMap two"); treemap.put(s3, "TreeMap three"); treemap.put(s4, "TreeMap four"); for(Map.Entry
           
             entry: treemap.entrySet()) { System.out.println("The treemap key is "+entry.getKey().a+" The value is "+ entry.getValue()); }*/ //HasMap System.out.println("\nHashMap......"); Map
            
              hashmap=new HashMap
             
              (); hashmap.put(s1, "HashMap one"); hashmap.put(s2, "HashMap two"); hashmap.put(s3, "HashMap three"); hashmap.put(s4, "HashMap four"); for(Map.Entry
              
                entry : hashmap.entrySet()) { System.out.println("The key is "+entry.getKey().a+" The value is "+entry.getValue()); } //HasTable System.out.println("\nHashTable......"); Map
               
                 hashtable=new Hashtable
                
                 (); hashtable.put(s1, "HashTable one"); hashtable.put(s2, "HashTable two"); hashtable.put(s3, "HashTable three"); hashtable.put(s4, "HashTable four"); for(Map.Entry
                 
                   entry: hashtable.entrySet()) { System.out.println("The HashTable key is "+entry.getKey().a+" The HashTable value is "+entry.getValue()); } //LinkedList System.out.println("\nLinkedList....."); List list=new LinkedList(); list.add(s1); list.add(s2); list.add(s3); list.add(s4); Iterator listit=list.iterator(); while(listit.hasNext()) { setClass ob=(setClass)listit.next(); System.out.println(ob.a); } //ArrayList System.out.println("\nArrayList....."); List array=new ArrayList(); array.add(s1); array.add(s2); array.add(s3); array.add(s4); Iterator arrayit=array.iterator(); while(arrayit.hasNext()) { setClass ob=(setClass)arrayit.next(); System.out.println(ob.a); } //vector System.out.println("\nvector....."); Vector v=new Vector(); v.add(s1); v.add(s2); v.add(s3); v.add(s4); Iterator vit=v.iterator(); while(vit.hasNext()) { setClass ob=(setClass)vit.next(); System.out.println(ob.a); } }}

输出结果：

由于没有重写hasCode和equals方法，所以s3和s4对象认为是不相同的，因此在set中被看成了不同的对象；同理，在hashMap和hashTable中，其根据hashCode的值对数据进行存储的，所以，hashcode的值不一样，因此也存储了4个数。

hasSet......http://www.yjbys.com1/http://www.yjbys.com2/http://www.yjbys.com/http://www.yjbys.com2/HashMap......The key is http://www.yjbys.com1/ The value is HashMap twoThe key is http://www.yjbys.com2/ The value is HashMap fourThe key is http://www.yjbys.com/ The value is HashMap oneThe key is http://www.yjbys.com2/ The value is HashMap threeHashTable......The HashTable key is http://www.yjbys.com2/ The HashTable value is HashTable fourThe HashTable key is http://www.yjbys.com2/ The HashTable value is HashTable threeThe HashTable key is http://www.yjbys.com1/ The HashTable value is HashTable twoThe HashTable key is http://www.yjbys.com/ The HashTable value is HashTable oneLinkedList.....http://www.yjbys.com/http://www.yjbys.com1/http://www.yjbys.com2/http://www.yjbys.com2/ArrayList.....http://www.yjbys.com/http://www.yjbys.com1/http://www.yjbys.com2/http://www.yjbys.com2/vector.....http://www.yjbys.com/http://www.yjbys.com1/http://www.yjbys.com2/http://www.yjbys.com2/

改变之后的。

基础类：

package niukewang;import java.util.Objects;public class setClass {    String a;    String b;    public setClass(String a, String b)    {        this.a=a;        this.b=b;        }        public int hashCode() {        return a.hashCode();    }        public boolean equals(Object obj)    {        if(obj==null) return false;                if(getClass() != obj.getClass()) return false;                final setClass s=(setClass)obj;                return Objects.equals(this.a, s.a);    }}

测试类：

package niukewang;import java.util.ArrayList;import java.util.HashMap;import java.util.HashSet;import java.util.Hashtable;import java.util.Iterator;import java.util.LinkedList;import java.util.List;import java.util.Map;import java.util.Map.Entry;import java.util.Set;import java.util.TreeMap;import java.util.TreeSet;import java.util.Vector;public class test1 {    public static void main(String args[])     {         setClass s1=new setClass("http://www.yjbys.com/", "");        setClass s2=new setClass("http://www.yjbys.com1/", "");        setClass s3=new setClass("http://www.yjbys.com2/", "");        setClass s4=new setClass("http://www.yjbys.com2/", "");                //hasSet        System.out.println("hasSet......");        Set
     
       set=new HashSet
      
       ();        set.add(s1);        set.add(s2);        set.add(s3);        set.add(s4);        Iterator it= set.iterator();        while(it.hasNext())        {            setClass ob=(setClass)it.next();            System.out.println(ob.a);        }        /*        //TreeSet        System.out.println("\nTreeSet........");        Set
       
         tree=new TreeSet
        
         ();        tree.add(s1);        tree.add(s2);        tree.add(s3);        tree.add(s4);        Iterator treeit=tree.iterator();        while(treeit.hasNext())        {            setClass ob=(setClass) treeit.next();            System.out.println(ob.a);        }        */        //TreeMap/*        System.out.println("\nTreeMap.........");        Map
         
           treemap=new TreeMap
          
           (); treemap.put(s1, "TreeMap one"); treemap.put(s2, "TreeMap two"); treemap.put(s3, "TreeMap three"); treemap.put(s4, "TreeMap four"); for(Map.Entry
           
             entry: treemap.entrySet()) { System.out.println("The treemap key is "+entry.getKey().a+" The value is "+ entry.getValue()); }*/ //HasMap System.out.println("\nHashMap......"); Map
            
              hashmap=new HashMap
             
              (); hashmap.put(s1, "HashMap one"); hashmap.put(s2, "HashMap two"); hashmap.put(s3, "HashMap three"); hashmap.put(s4, "HashMap four"); for(Map.Entry
              
                entry : hashmap.entrySet()) { System.out.println("The key is "+entry.getKey().a+" The value is "+entry.getValue()); } //HasTable System.out.println("\nHashTable......"); Map
               
                 hashtable=new Hashtable
                
                 (); hashtable.put(s1, "HashTable one"); hashtable.put(s2, "HashTable two"); hashtable.put(s3, "HashTable three"); hashtable.put(s4, "HashTable four"); for(Map.Entry
                 
                   entry: hashtable.entrySet()) { System.out.println("The HashTable key is "+entry.getKey().a+" The HashTable value is "+entry.getValue()); } //LinkedList System.out.println("\nLinkedList....."); List list=new LinkedList(); list.add(s1); list.add(s2); list.add(s3); list.add(s4); Iterator listit=list.iterator(); while(listit.hasNext()) { setClass ob=(setClass)listit.next(); System.out.println(ob.a); } //ArrayList System.out.println("\nArrayList....."); List array=new ArrayList(); array.add(s1); array.add(s2); array.add(s3); array.add(s4); Iterator arrayit=array.iterator(); while(arrayit.hasNext()) { setClass ob=(setClass)arrayit.next(); System.out.println(ob.a); } //vector System.out.println("\nvector....."); Vector v=new Vector(); v.add(s1); v.add(s2); v.add(s3); v.add(s4); Iterator vit=v.iterator(); while(vit.hasNext()) { setClass ob=(setClass)vit.next(); System.out.println(ob.a); } }}

输出结果：

由于覆盖了hashCode和equals方法，因此s3和s4被认为是相同的对象。

hasSet......http://www.yjbys.com1/http://www.yjbys.com/http://www.yjbys.com2/HashMap......The key is http://www.yjbys.com1/ The value is HashMap twoThe key is http://www.yjbys.com/ The value is HashMap oneThe key is http://www.yjbys.com2/ The value is HashMap fourHashTable......The HashTable key is http://www.yjbys.com1/ The HashTable value is HashTable twoThe HashTable key is http://www.yjbys.com/ The HashTable value is HashTable oneThe HashTable key is http://www.yjbys.com2/ The HashTable value is HashTable fourLinkedList.....http://www.yjbys.com/http://www.yjbys.com1/http://www.yjbys.com2/http://www.yjbys.com2/ArrayList.....http://www.yjbys.com/http://www.yjbys.com1/http://www.yjbys.com2/http://www.yjbys.com2/vector.....http://www.yjbys.com/http://www.yjbys.com1/http://www.yjbys.com2/http://www.yjbys.com2/

但是TreeSet和TreeMap还是不能这么输出，因为要实现Comparable接口。因为TreesSet和TreeMap是一个有序的集合，必须知道你想怎么排列。你可以换成LinkedList或ArrayList就不用了。

下一篇文章是对TreeSet和TreeMap的输出。

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