Java忽略布尔值评估

Question

if (!(portField.getText().equals(""))) {                
    String p = portField.getText();
    CharSequence numbers = "0123456789";

    if (p.contains(numbers)) {

        listener = new ServerSocket(Integer.parseInt(p));

        while (true) {
            Socket socket = listener.accept();
            try {
                PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
                out.println("Hi there, human.");    
            } finally {
                socket.close(); 
            }
    }} else {
        JOptionPane.showMessageDialog(null, "Only numbers are allowed.");
    }
} else {
    JOptionPane.showMessageDialog(null, "Please input a port.");
}

The problem is: The JOptionPane pops up saying "Only numbers are allowed" even when I put numbers in the portField . The CharSequence and the way I've tested it to allow only numbers to be input, as far as I know, is correct, and Java ignores the whole block and jumps to the else clause.

Why is this happening? Should I not use else and use else if instead?

Answer 1

contains means contains the whole 0123456789 . For example: "a0123456789b"

Use p.matches("[0-9]*"); instead.