Collection常用方法說明
代碼示例
運行結果
public static void main(String[] args) {
//Collection介面說明
Collection<String> list = new ArrayList<>();
System.out.println(list.size());
System.out.println(list.isEmpty());
list.add("a");
list.add("b");
list.add("c");
System.out.println(list.size());
System.out.println(list.isEmpty());
Object[] array = list.toArray();//回傳一個裝有所有集合中元素的陣列
System.out.println(Arrays.toString(array));
for (String s:list) {
System.out.println(s);
}
list.remove("b");
for (String s :list) {
System.out.println(s);
}
list.clear();
System.out.println(list.size());
System.out.println(list.isEmpty());
}
Map常用方法說明
代碼示例
public static void main6(String[] args) {
//Map介面說明
Map<String,String> map = new HashMap<>();
System.out.println(map.size());
System.out.println(map.isEmpty());
//get根據指定的k查找對應的v
System.out.println(map.get("s"));
map.put("作者","魯迅");//將指定的 k-v 放入 Map
map.put("標題","狂人日記");
System.out.println(map.size());
System.out.println(map.isEmpty());
System.out.println(map.get("作者"));
System.out.println(map.get("標題"));
//根據指定的k查找對應的v，沒有找到用默認值代替
System.out.println(map.getOrDefault("作者","徐海濤"));
System.out.println(map.getOrDefault("武俠","徐海濤"));
System.out.println(map.containsKey("作者"));//判斷是否包含 key
//將所有鍵值對回傳
for (Map.Entry<String,String>entry: map.entrySet()) {
System.out.println(entry.getKey());
System.out.println(entry.getValue());
}
}
運行結果
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標籤：java