java常见集合的循环输出方式
常见集合的循环输出方式
一、List集合的循环输出
List<Object> objList = new ArrayList<Object>();
1) for (int i=0; i<objList.size(); i++)
{
// 循环输出集合中的每个对象
Object object = objList.get(i);
System.out.println(object);
}
2) for (Object obj:objList)
{
// 循环输出集合中的每个对象
System.out.println(object);
}
3) 将List集合转换为迭代器Iterator接口，并且循环输出
List<String> list = new ArrayList<String>();
list.add("cheng");
list.add("zhang");
Iterator it = list.iterator();
while (it.hasNext())
{
String str = (String)it.next();
System.out.println(str);
}
4) 将List集合转换为Object类型的数组,循环输出
List<String> list = new ArrayList<String>();
list.add("cheng");
list.add("zeng"); list.add("zhang");
Object[] obj = list.toArray();
for (int i=0; i<obj.length; i++)
{
String s = (String)obj[i];
System.out.println(s);
}
二.循环输出Set<E>
1) 将Set集合转换为迭代器Iterator接口，并且循环输出
Set<String> set = new HashSet<String>();
set.add("cheng");
set.add("zeng");
set.add("zhang");
Iterator it = set.iterator();
while (it.hasNext())
{
String str = (String)it.next();
System.out.println(str);
}
2) 将Set集合转换为Object类型的数组
Set<String> set = new HashSet<String>();
set.add("cheng");
set.add("zeng");
set.add("zhang");
Object[] obj = set.toArray();
for (int i=0;i<obj.length;i++)
{
String s = (String)obj[i];
System.out.println(s);
}
三.循环输出Map<K,V> 1) 直接循环Map对象
Map<String,String> map = new HashMap<String, String>();
map.put("1","cheng");
map.put("2","zeng");
map.put("3","zhang");
// 输出键值
for (String key:map.keySet())
{
System.out.println(key);
}
// 输出value
for (String value:map.values())
{
System.out.println(value);
}
2) Map<String,String> map = new HashMap<String, String>();
map.put("1","cheng");
map.put("2","zeng");
map.put("3","zhang");
Iterator it = map.entrySet().iterator();
while (it.hasNext())
{
Map.Entry<String, String> s = (Map.Entry<String, String>)it.next(); System.out.println(s);
}
输出结果： 3=zhang 2=zeng 1=cheng