Hello! I'm creating something sort of like a turn-based battle system to sharpen my Java skills, but I'm getting this error on lines 40 and 44, and I'm not exactly sure why. Here's my code:

import javax.swing.*;
import java.io.*;
import java.util.Random;
class TBBS
{
	public static void main(String[]args)
	{
	    int attackbonus, defensebonus, hpbonus, enemyhp, enemyattack, enemydefense, hp, attack, defense, level, s1;
		String select, s;
		enemyhp=5;
		enemyattack=1;
		enemydefense=0;
		hp=10;
		attack=2;
		defense=0;
		level=1;
 
		JOptionPane.showMessageDialog(null, "Welcome to the battle system!", "Welcome!", JOptionPane.INFORMATION_MESSAGE);
		Options(s);
 
	}	
 
	static void Options(String s)
	{
	  Object[] possibility = {"Attack", "Defend"};
		s = (String)JOptionPane.showInputDialog(null, "What do you want to do?", "Action Commands", JOptionPane.PLAIN_MESSAGE,
		null, possibility, "");
 
	}
   static void levelup(String b, int level)
	{
		int attack, defense, hp, s1;
		level=(level+1);
		Object[] levelup = {"Attack", "Defense", "HP"};
		b = (String)JOptionPane.showInputDialog(null, "You've grown to level " + level + "! Which stat do you want to increase?", "Level Up!", JOptionPane.PLAIN_MESSAGE,
		null, levelup, "");
 
		s1=Integer.parseInt(b);
 
		if (s1=1)
		{
			attack=(attack+1);
		}	
		else if (s1=2)
		{
			defense=(defense+1);
		}
		else
		{
			hp=(hp+5);
		}		
	}
}

Any help would be greatly appreciated!