package scheduler;

import os.OperatingSystem;
import readinstruction.ReadInstruction;

import java.util.LinkedList;
import java.util.Queue;

/**
 * Created by Karol on 2017-04-20.
 */
public class FcfsScheduler implements Scheduler {
    private Queue<ReadInstruction> waitingQueue;
    private OperatingSystem parentOs;

    public FcfsScheduler(){
        this.waitingQueue = new LinkedList<>();
    }

    @Override
    public void setOs(OperatingSystem parentOs) {
        this.parentOs = parentOs;
    }

    @Override
    public void push(ReadInstruction instruction) {
        this.waitingQueue.add(instruction);
    }

    @Override
    public String getName() {
        return null;
    }

    @Override
    public void update(int time) {

    }
}

package scheduler;

import os.OperatingSystem;
import readinstruction.ReadInstruction;

import java.util.LinkedList;
import java.util.Queue;

/**
 * Created by Karol on 2017-04-20.
 */
public class FcfsScheduler implements Scheduler {
    private Queue<ReadInstruction> waitingQueue;
    private OperatingSystem parentOs;
    private int headPosition;

    public FcfsScheduler(){
        this.waitingQueue = new LinkedList<>();
        this.headPosition = 0;
    }

    @Override
    public void setOs(OperatingSystem parentOs) {
        this.parentOs = parentOs;
    }

    @Override
    public void push(ReadInstruction instruction) {
        this.waitingQueue.add(instruction);
    }

    @Override
    public String getName() {
        return null;
    }

    @Override
    public void update(int time) {
        if (this.waitingQueue.peek().getReadAddress() > this.headPosition) this.headPosition++;
        if (this.waitingQueue.peek().getReadAddress() < this.headPosition) this.headPosition--;
        if (this.waitingQueue.peek().getReadAddress() == this.headPosition){
            this.waitingQueue.peek().read(time);
            this.parentOs.push(this.waitingQueue.remove());
        }
    }
}

Implement update method in FcfsScheduler