SJFScheduling.java

package algorithms;

import java.util.Arrays;
import java.util.Comparator;

public class SJFScheduling {

	public void schedule(Process[] processes) {
		// Sort processes by arrival time first
		Arrays.sort(processes, Comparator.comparingInt(p -> p.arrivalTime));

		int currentTime = 0;
		int completedProcesses = 0;
		int totalProcesses = processes.length;
		boolean[] completed = new boolean[totalProcesses];

		while (completedProcesses < totalProcesses) {
			int shortestJobIndex = -1;
			int shortestBurstTime = Integer.MAX_VALUE;

			// Find the process with shortest burst time that has arrived
			for (int i = 0; i < totalProcesses; i++) {
				if (!completed[i] && processes[i].arrivalTime <= currentTime
						&& processes[i].burstTime < shortestBurstTime) {
					shortestBurstTime = processes[i].burstTime;
					shortestJobIndex = i;
				}
			}

			// If no process is available at current time
			if (shortestJobIndex == -1) {
				currentTime++;
				continue;
			}

			// Process the selected process
			Process selectedProcess = processes[shortestJobIndex];
			selectedProcess.startTime = currentTime;
			currentTime += selectedProcess.burstTime;
			selectedProcess.completionTime = currentTime;
			selectedProcess.turnAroundTime = selectedProcess.completionTime
					- selectedProcess.arrivalTime;
			selectedProcess.waitingTime = selectedProcess.turnAroundTime
					- selectedProcess.burstTime;

			completed[shortestJobIndex] = true;
			completedProcesses++;
		}
	}

	// Calculate and return average waiting time
	public double getAverageWaitingTime(Process[] processes) {
		double totalWaitingTime = 0;
		for (Process p : processes) {
			totalWaitingTime += p.waitingTime;
		}
		return totalWaitingTime / processes.length;
	}

	// Calculate and return average turnaround time
	public double getAverageTurnaroundTime(Process[] processes) {
		double totalTurnaroundTime = 0;
		for (Process p : processes) {
			totalTurnaroundTime += p.turnAroundTime;
		}
		return totalTurnaroundTime / processes.length;
	}
}