Use a simple method to directly judge the sum of the @ symbol. The symbol should be a possible input string. index of(' @ ')= =- 1； It means no, the same judgment point. To be more precise, you can judge that there is an @ after it. In this way, you can use the input string. Index of ("@") to determine whether there are numbers after test.indexof ("."), 5, 2). Here, 5 starts with the fifth, which can be replaced by the input string. Indexof('@') and then the second is to find a few. Here you can write 100.