Read my own printed line in console

Question

Is there a way in which, from a function, I print a String in with System.out.print() and then read it from another function?

something like:

void printC(String foo){
    System.out.print(foo);
}

void read(){
    String c;
    while(something){
        printC(somethingElse);
        c = System.console.readLine();
        JOptionPane.showMessageDialog(c);
    }
}

is there a reason that you must print your string to console instead of, say, having `printC` return it? Or just passing it to `showMessageDialog` directly? — Dan O, May 04 '14 at 22:42
Even if someone answers this question, you should definitely not do this. This sounds like the sort of design decision that we would end up reading about on theDailyWTF.com — allTwentyQuestions, May 04 '14 at 22:53
I want to do this because I'm overriding MouseCLick function in MouseAdapter, and this function is void, is there a way to change this? — StAx, May 04 '14 at 23:09

score 2 · Answer 1 · answered May 04 '14 at 23:52

No, you can't. As other people have commented, you probably just want an internal data structure to connect different components.

In command-line programs, the standard input and standard output (plus standard error) are completely independent streams. It's typical for all three to be connected to a single virtual terminal, but they can be redirected independently from the shell, such as by using a pipeline or files.

Think about what if the input of your program is coming from a file and the output is being piped to another program; trying to "get back" the output doesn't make any sense.

Syam S · Accepted Answer · 2014-05-05T00:09:18.610

1

Try PipedOutputStream.

import java.io.IOException;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
import java.io.PrintStream;
import java.util.Scanner;

import javax.swing.JFrame;
import javax.swing.JOptionPane;


public class Test extends JFrame {

    void printC(String foo){
        System.out.print(foo);
    }

    void read() throws IOException{
        String c = "";
        PipedOutputStream pipeOut = new PipedOutputStream();
        PipedInputStream pipeIn = new PipedInputStream(pipeOut);
        System.setOut(new PrintStream(pipeOut));
        Scanner sc = new Scanner(pipeIn);
        while(!c.equalsIgnoreCase("Quit")){
        printC("Test\n");
        c = sc.nextLine();
        JOptionPane.showMessageDialog(this, c);
        }
    }

    public static void main(String[] args) throws IOException {
        Test t = new Test();
        t.read();
    }

}

edited May 05 '14 at 00:09

answered May 04 '14 at 23:07

Syam S

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How? didnt get the output? – Syam S May 04 '14 at 23:40
this works, but it isn't what I'm looking for, I want to read something that other function prints, not an keyboard input – StAx May 05 '14 at 00:17
The last edit worked perfectly, Thaaaaaaaaaaaaaanks <3 – StAx May 05 '14 at 00:25

score 1 · Answer 3 · answered May 04 '14 at 23:20

Why do you want to do this? Is it so that you can print something to the screen or so that you can create events?

If you particularly want to pass messages to the screen AND also another part of your application; a simple solution could involve creating your own PrintStream class. You can deal with the object in the same way as you would otherwise deal with System.out (as that's a PrintStream too).

Something along the lines of this:

public class FancyStream extends PrintStream
{
    LinkedList<String> messageQueue = new LinkedList<>();

    @Override
    public void println(String line)
    {
        System.out.println(line);
        messageQueue.add(line);
    }

    public String getLine()
    {
        return messageQueue.pop();
    }
}

However, if you want events (as you've suggested in the comments), this is not the way to do it! You should take a look at the Observer pattern for dealing with events. The wikipedia article about this is here.

There's plenty of other resources to learn about the Observer pattern if you do a Google search. Java even has a built in Observable class and Observer interface that may solve your problem.

Read my own printed line in console

3 Answers3