How to mimic fork and pipes in Java?

Question

I am working on an assignment where I have to implement a basic CPU and memory module using Process as "fork" and InputStream/OutputStream as the "pipes". I am having trouble getting the basic communication back and forth working correctly.

My code for CPU is:

public static void main(String[] args) {
    try {
        Runtime rt = Runtime.getRuntime();
        Process proc = rt.exec("java Memory.java " + "testInput.txt"); 

        InputStream is = proc.getInputStream();
        OutputStream os = proc.getOutputStream();

        Scanner fromMem = new Scanner(is);
        PrintWriter toMem = new PrintWriter(os);

        //Now the main loop
        IR = 0;
        PC = 0;
        while(IR != 50){       //END command
            System.out.println("PC: " + PC);
            //Get the next instruction
            toMem.println("READU");
            toMem.println(PC);
            toMem.flush();
            String temp = fromMem.nextLine();
            System.out.println(temp);

            PC++;
        }
    }catch (Throwable t){
        t.printStackTrace();
    }
}

And my code for Memory.java is:

static int[] mem = new int[2000];

public static void main(String[] args) {
    initMemory(args[0]);    //Fills the mem array with values from input file
    Scanner fromCPU = new Scanner(System.in);
    String input = "";
    while(input != "END"){
        int toSend;
        input = fromCPU.nextLine();
        switch (input){
            case "READU":   toSend = read(Integer.parseInt(fromCPU.nextLine()),true);       //returns value at given address in memory
                            System.out.println(toSend); //Send the value returned from memory
                            break;
            default:        break;

        }
    }
}

static int read(int address,Boolean userMode){
    if(userMode && address > 999){
        System.out.println("Memory Violation. Accessing system address " + address + " in user mode.");
        return -999999999;
    }
    return mem[address];

}

My input file has the following text:

1 2 3

If I just run Memory.java it works just fine with reading "READU", then an address, then it prints out the value at that address in the memory array. However, when I run CPU, I get java.util.NoSuchElementException: No line found from the String temp = fromMem.nextLine(); line in CPU.

Hopefully my question is clear. I have taken out any code that doesn't affect this problem I am having. Please let me know if you need to see any other code.

Thank you.