How to write getch() in NACHOS (Java)?

Question

So I am learning to create my own SerialConsole in nachos (Java). I learned using Semaphore.P() and Semaphore.V() to wait for user input. Everything is going well until I tried to make a function like getch() in C's conio.h.

The problem is, whenever I called Semaphore.P(), even though the Semaphore.V() is called, it will always wait for Enter key to be pressed before it resume the program. I wanted the program to resume whenever I press a key.

Below is some code I tried.

Console.java

public class Console {
    private SerialConsole console;
    private Semaphore sem = new Semaphore(0);
    private Runnable send, recv;
    private char tempChar;

    public Console() {
        console = Machine.console();
        send = new Runnable() {

            @Override
            public void run() {
                sem.V();
            }
        };
        recv = new Runnable() {

            @Override
            public void run() {
                tempChar = (char) console.readByte();
                sem.V();
            }
        };
        console.setInterruptHandlers(recv, send);
    }

    public String nextLine() {
        String result = "";

        do {
            sem.P();
            if (tempChar != '\n') result += tempChar;
        } while(tempChar != '\n');

        return result;
    }

    public char getch() {
        sem.P();
        return tempChar;
    }
}

Main.java

public class Main {
    private Console console;

    public Main() {
        console = new Console();
        char c = console.getch();
        System.out.println(c);
    }
}

Is there anything I have missed or is there any way to programmatically press Enter key or something?

PS: java.awt.Robot can't be used inside a nachos project.

Any help would be appreciated.