常見集合的迴圈輸出方式
一、List集合的迴圈輸出
List<Object> objList = new ArrayList<Object>();
1) for (int i=0; i<objList.size; i++)
{
// 迴圈輸出集合中的每個物件
Object object = objList.get(i);
System.out.println(object);
}
2) for (Object obj:objList)
{
// 迴圈輸出集合中的每個物件
System.out.println(object);
}
3) 將List集合轉換為迭代器Iterator介面,並且迴圈輸出
List<String> list = new ArrayList<String>();
list.add("cheng");
list.add("zeng");
list.add("zhang");
Iterator it = list.iterator();
while (it.hasNext())
{
String str = (String)it.next();
System.out.println(str);
}
4) 將List集合轉換為Object型別的陣列,迴圈輸出
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.迴圈輸出Set<E>
1)
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) 將Set集合轉換為Object型別的陣列
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.迴圈輸出Map<K,V>
1) 直接迴圈Map物件
Map<String,String> map = new HashMap<String, String>();
map.put("1","cheng");
map.put("2","zeng");
map.put("3","zhang");
// 輸出鍵值
for (String key:map.keySet())
{
System.out.println(key);
}
// 輸出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);
}
輸出結果:
3=zhang
2=zeng
1=cheng