java - 使用 PrintWriter 打印字符串

Question

尝试使用 PrintWriter 打印时遇到问题。

问题描述:

I am expecting to print the Press options first then take the user input but using out.println i can't do that. It's not printing the options while i run the program. It just waits for an input while i give the input it then prints the Press options.

注意: 如果我使用 System.out.println 那么它会按预期工作。

尝试如下

public class Calculator {
    public static void main(String[] args) throws IOException {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out =  new PrintWriter(new OutputStreamWriter(System.out));
        StringTokenizer took = new StringTokenizer(" ");
        String operator;
//            System.out.println("Press '+' for Additon");
//            System.out.println("Press '-' for Subtraction");
//            System.out.println("Press '*' for multiplication");
        out.println("Press '+' for Additon");
        out.println("Press '-' for Subtraction");
        out.println("Press '*' for multiplication");
        out.println("Press '/' for Division");

        operator=in.readLine();
        switch (operator) {
            case "+":
                out.println("Add");
                break;
            case "-":
                out.println("Subtract");
                break;
            case "*":
                out.println("Multiply");;
                break;
            case "/":
                out.println("Division");
                break;
        }
        in.close();
        out.close();
    }
}

输入:

*

输出:

Press '+' for Additon
Press '-' for Subtraction
Press '*' for multiplication
Press '/' for Division

Multiply

Answer 1

做:

out.flush();

在读入之前，然后在关闭输出之前。

或者你可以这样做:

PrintWriter out =  new PrintWriter(new OutputStreamWriter(System.out), true);

true 的作用是将其设置为每次打印时自动刷新。

建议查看 PrintWriter 的 Javadoc .