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
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