集合Set、List、Map的遍历方法

 package com.shellway.javase;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.TreeMap;

 import org.junit.Test;

 public class TestCollection {

     public static void print(Collection<? extends Object> c){
         Iterator<? extends Object> it = c.iterator();
         while (it.hasNext()) {
             Object object = (Object) it.next();
             System.out.println(object);
         }
     }

     @Test
     public void demo1(){
         Set<String> set = new HashSet<String>();
         set.add("AAA");
         set.add("BBB");
         set.add("CCC");
         print(set);

         //Set的第一种遍历方式:利用Iterator
         Iterator<String> it1 = set.iterator();
         for (String ss : set) {
             System.out.println(ss);
         }
         //Set的第一种遍历方式:利用foreach
         for (String sss : set) {
             System.out.println(sss);
         }

         List<String> list = new ArrayList<String>();
         list.add("DDDDD");
         list.add("EEEEE");
         list.add("FFFFF");
         print(list);

         //List的第一种遍历方式:因为list有顺序，利用size()和get()方法获取
         for (int i = 0; i < list.size(); i++) {
             System.out.println(list.get(i));
         }
         //List的第二种遍历方式：利用Iterator
         Iterator<String> it = list.iterator();
         while (it.hasNext()) {
             System.out.println(it.next());
         }
         //List的第三种遍历方式:利用foreach
         for (String s2 : list) {
             System.out.println(s2);
         }

         Map<String,String> map = new TreeMap<String, String>();
         map.put("Jerry", "10000");
         map.put("shellway", "20000");
         map.put("Kizi", "30000");
         print(map.entrySet());
         //Map的第一种遍历方式：先获得key,再获得值value
         Set<String> sett = map.keySet();
         for (String s : sett) {
             System.out.println(s+":"+map.get(s));
         }
         //Map的第二种遍历方式：获得键值对
         for (Map.Entry<String, String> entry : map.entrySet()) {
             System.out.println(entry.getKey()+" : "+entry.getValue());
         }
     }
 }

使用泛型对集合对象进行类型安全检查和遍历