How to take two inputs one after another and have the second one not output the same as the first one?

I am making a minigame plugin and I want to have the player define a region for the game by right-clicking two opposite corners. My idea was to have the code tell you to click one block and once you select a block it would tell you to pick a second one. After that, it would continue and open a GUI to finish creating the minigame. My first attempt made it so after you select the first block it switch a variable saying that the first corner was selected and then have another if statement waiting for you to select the next corner. But when it would switch the variable it would instantly run the next if statement and set both blocks at the same time.

@EventHandler
public void onRightClick(PlayerInteractEvent event) {
    Player player = event.getPlayer();
    Integer pos = 0;

    if (event.getAction().equals(Action.RIGHT_CLICK_BLOCK)) {
        if (event.getHand() == EquipmentSlot.OFF_HAND) {
            return;
        }
        if (player.getItemInHand().equals(MapSelectorTool.MapSelector)) {

            Block block = event.getClickedBlock();
            String world = block.getWorld().getName();
            Integer X = block.getX();
            Integer Y = block.getY();
            Integer Z = block.getZ();

            if (pos.equals(0)) {
                String[] pos1 = {
                    X.toString(),
                    Y.toString(),
                    Z.toString(),
                    world
                };
                player.sendMessage(ChatColor.GOLD + "First position at " + ChatColor.WHITE + ChatColor.BOLD + X + " " + Y + " " + Z + " " + ChatColor.GOLD + "now right click second position");
                pos = 1;


            }
        }
    }
}

The issue is that you are using a local variable inside the onRightClick method, for example Integer pos = 0; will always be reset with every right click. You need to store the variable outside of the method so that it is persistent for the second click, otherwise you can never do two separate clicks and link them.

//Place the key variables outside of the method/event (They may need to be static depending on how you wrote the code)
Player player;
Integer pos = 0;
String[] pos1;
String[] pos2;
public void onRightClick(PlayerInteractEvent event) {
player = event.getPlayer();
if (event.getAction().equals(Action.RIGHT_CLICK_BLOCK)) {
if (event.getHand() == EquipmentSlot.OFF_HAND) {
return;
}
if (player.getItemInHand().equals(MapSelectorTool.MapSelector)) {
Block block = event.getClickedBlock();
String world = block.getWorld().getName();
Integer X = block.getX();
Integer Y = block.getY();
Integer Z = block.getZ();
if (pos.equals(0)) {
pos1 = {X.toString(), Y.toString(), Z.toString(), world};
player.sendMessage(ChatColor.GOLD + "First position at " + ChatColor.WHITE + ChatColor.BOLD + X + " " + Y + " " + Z + " " + ChatColor.GOLD + "now right click second position");
pos = 1;
}
else if (pos.equals(1)) {
pos2 = {X.toString(), Y.toString(), Z.toString(), world};
player.sendMessage(ChatColor.GOLD + "Second position at " + ChatColor.WHITE + ChatColor.BOLD + X + " " + Y + " " + Z);
pos = 0;
//Now do your other code to process the positions and create the region?, and/or pass the variables to your game method to get it all setup?
//-----------------------
//yourGameMethod(pos1, pos2, player)
//-----------------------
player.sendMessage(ChatColor.GOLD + "Region created, have fun");
}
}
}
}

Caution: This code may only work for one player at a time depending on how you setup the plugin or trigger the events. If two players are using it at the same time then their clicks may get mixed up. To solve this you need to associate the clicks with a player, and store them in a list so that you can easily match them up when lots of players are using the plugin, and you could include a timeout function to reset the pos to 0 if the second click is not made within several minutes.

Integer pos = 0;
...
if (pos.equals(0)) {...}

Your static Integer object pos never changes?!

EDIT: Take a look at: https://javatutorialhq.com/java/lang/integer-class-tutorial/