How to fix this error in my code

Error: Main method not found in class Assignment, please define the main method as: public static void main(String[] args) and allow it to run

import java.lang.Math;

public class Assignment { private String name; private int effort; private int resources; private int difficulty; private double score;

public Assignment(int effort, int resources, int difficulty) { this.effort = effort; this.resources = resources; this.difficulty = difficulty; this.score = 0.1 * (effort * difficulty + (resources * effort)*2 / (Math.PI * difficulty)); }

public String getName() { return name; }

public int getEffort() { return effort; }

public int getResources() { return resources; }

public int getDifficulty() { return difficulty; }

public double getScore() { return score; } }

class AssignPlan { private int numAssignments; private int numComplete; private double totalPoints; private int hoursAvailable; private String highestPriorityItem;

public AssignPlan() { this.numAssignments = 0; this.numComplete = 0; this.totalPoints = 0; this.hoursAvailable = 0; this.highestPriorityItem = ""; }

public AssignPlan(int numAssignments, int numComplete, double totalPoints, int hoursAvailable, String highestPriorityItem) { this.numAssignments = numAssignments; this.numComplete = numComplete; this.totalPoints = totalPoints; this.hoursAvailable = hoursAvailable; this.highestPriorityItem = highestPriorityItem; }

public int getNumAssignments() { return numAssignments; }

public int getNumComplete() { return numComplete; }

public double getTotalPoints() { return totalPoints; }

public int getHoursAvailable() { return hoursAvailable; }

public String getHighestPriorityItem() { return highestPriorityItem; }

public void setHighestPriorityItem(String highestPriorityItem) { this.highestPriorityItem = highestPriorityItem; }

public void getUrgentAssignment(String name, int effort, int resources, int difficulty) { Assignment a = new Assignment(effort, resources, difficulty); this.highestPriorityItem = a.getName(); this.numAssignments++; this.numComplete++; this.hoursAvailable -= a.getEffort(); this.totalPoints += a.getScore(); } }