Java -如何验证以下输入格式'operand operator operand‘(例如1.4 * 5)

Question

我在绞尽脑汁想弄清楚我的代码出了什么问题。我要求用户插入以下格式：

LeftOperand operator RightOperand

其中：

可以是任意int或number

• operator -可以是+、-、*或/

• RightOperand -可以是任意int或浮点数

。

我搜索并找到了很少的正则表达式，但它们似乎都不适合我，因为除了以下内容：3 +/-/*// 5返回一个错误。应有效：

• 1 + 3
• 1 / 4
• 1.3 - 4
• 4 -5.3

H 119123*3434H 220H 12112.34*485H 222f 223

但实际上，只有这些内容是有效的，而其余的返回错误：

• 1 +3-更正
• 1/4-更正
• 1.3-4-错误
• 4- 5.3 -错误

<代码>H 133123* 3434 -错误<代码>H 234<代码>H 13512.34* 485 -错误<代码>H 236<代码>F 237

我目前正在代码中使用以下regex：

"[((\\d+\\.?\\d*)|(\\.\\d+))] [+,\\-,*,/] [((\\d+\\.?\\d*)|(\\.\\d+))]"

试过各种方法，但似乎都没有用，我只是不知道我做错了什么：

[[+-]?([0-9]*[.])?[0-9]] [+,\-,*,/] [[+-]?([0-9]*[.])?[0-9]]

这是我的客户代码：

private static final int SERVER_PORT = 8080;
private static final String SERVER_IP = "localhost";
private static final Scanner sc = new Scanner(System.in);
private static final String regex = "[((\\d+\\.?\\d*)|(\\.\\d+))] [+,\\-,*,/] [((\\d+\\.?\\d*)|(\\.\\d+))]";

public static void main(String[] args) throws IOException {
    // Step 1: Open the socket connection
    Socket serverSocket = new Socket(SERVER_IP, SERVER_PORT);

    // Step 2: Communication-get the input and output stream
    DataInputStream dis = new DataInputStream(serverSocket.getInputStream());
    DataOutputStream dos = new DataOutputStream(serverSocket.getOutputStream());

    //Run until Client decide to disconnect using the exit phrase
    while (true) {
        // Step 3: Enter the equation in the form -
        // "operand1 operation operand2"
        System.out.print("Enter the equation in the form: ");
        System.out.println("'operand operator operand'");

        String input = sc.nextLine();
        // Step 4: Checking the condition to stop the client
        if (input.equals("exit"))
            break;

        //Step 4: Check the validity of the input and
        // return error message when needed
        if (input.matches(regex)) {
            System.out.println("Expression is correct: " + input);
        } else {
            System.out.println("Expression is incorrect, please try again: ");
            continue;
        }

        // Step 5: send the equation to server
        dos.writeUTF(input);

        // Step 6: wait till request is processed and sent back to client
        String ans = dis.readUTF();
        // Step 7: print the response to the console
        System.out.println("Answer=" + Double.parseDouble(ans));
    }
}

Answer 1

private static final String NUM = "(-?\\d+(\\.\\d*)?)";
private static final String OP = "([-+*/])"; // Minus at begin to avoid confusion with range like a-z.
private static final String WHITESPACE = "\\s*";
private static final String regex = NUM + WHITESPACE + OP + WHITESPACE + NUM;

注意：

• $1对应于第一个number
• $3对应于第二个number
• (...)对应的是一个组($1，$2，.；$0是all)
• [...]是一个字符集，一个字符match
• X? X optional
• X* X0或更多times
• X+ X1或更多times
• \\s空间，tab
• \\d数字