使用PrintWriter打印字符串

Question

Facing problem while trying to print using PrintWriter.

Problem Description:

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.

Note: if i use System.out.println then it works as expected.

Tried it like below

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();
    }
}

Input:

*

Output:

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

Multiply

Answer 1

Do:

out.flush();

Before you read in, and then before you close the out .

Or you can do:

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

What the true does is sets it to auto flush every time you print.

Suggest reviewing the Javadoc for the PrintWriter .