Java周遊Map和周遊Set
Java周遊Map
public static void main(String[] args) {
Map<String,String> map = new HashMap<String,String>();
map.put("1", "value1");
map.put("2", "value2");
map.put("3", "value3");
//第一種:普遍使用,二次取值
System.out.println("通過Map.keySet周遊key和value:");
for (String key : map.keySet()) {
System.out.println("key= "+ key + " and value= " + map.get(key));
}
//第二種
System.out.println("通過Map.entrySet使用iterator周遊key和value:");
Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<String, String> entry = it.next();
System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
}
//第三種:推薦,尤其是容量大時
System.out.println("通過Map.entrySet周遊key和value");
for (Map.Entry<String, String> entry : map.entrySet()) {
System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
}
//第四種
System.out.println("通過Map.values()周遊所有的value,但不能周遊key");
for (String v : map.values()) {
System.out.println("value= " + v);
}
}
Java周遊Set
對 set 的周遊 1.疊代周遊: Set<String> set = new HashSet<String>(); Iterator<String> it = set.iterator(); while (it.hasNext()) { String str = it.next(); System.out.println(str); } 2.for循環周遊: for (String str : set) { System.out.println(str); } 優點還展現在泛型 假如 set中存放的是Object Set<Object> set = new HashSet<Object>(); for循環周遊: for (Object obj: set) { if(obj instanceof Integer){ int aa= (Integer)obj; }else if(obj instanceof String){ String aa = (String)obj } ........ }