字符串、数组、集合
类型 长度获取的方法 示例 字符串String length() String str = "abc"
int length = str.length();
System.out.println(length);//3
数组Array length
int[] arr = new int[]{1,2,3,4,5};
int length = arr.length;
System.out.println(length);//5
ArrayList<Integer> list = new ArrayList<>();
int size = list.size();
System.out.println(size);//0
HashSet、HashMap集合 size()
HashSet<String> hashSet = new HashSet<>();
int size = hashSet.size();