depend.yml

name: MyPlugin
version: 1.0
depend: [WorldEdit]

selection.java

import com.sk89q.worldedit.bukkit.*;
import com.sk89q.worldedit.bukkit.selections.*;

WorldEditPlugin worldEdit = (WorldEditPlugin) Bukkit.getServer().getPluginManager().getPlugin("WorldEdit");
Selection selection = worldEditPlugin.getSelection(player);

if (selection != null) {
    World world = selection.getWorld();
    Location min = selection.getMinimumPoint();
    Location max = selection.getMaximumPoint();
    
    // Do something with min/max
} else {
    // No selection available
}

shape.java

import com.sk89q.worldedit.BlockVector2D; // Required for polygon points

if (selection instanceof CuboidSelection) { // Is it a cuboid?
    CuboidSelection cuboid = (CuboidSelection) selection;

} else if (selection instanceof Polygonal2DSelection) { // Is it a polygon?
    Polygonal2DSelection polygon = (Polygonal2DSelection) selection;
    List<BlockVector2D> points = getNativePoints();
    
    // Points are BlockVector2Ds, which are immutable
    // (you can't change their X, Y, Z without getting a new object)
    
    for (BlockVector2D point : points) {
        double x = point.getX();
        double z = point.getZ();
        
        // Or as an int
        getBlockX(), getBlockZ()
    }
    
} else {
    // It's a different shape
}

soft_depend.yml

name: MyPlugin
version: 1.0
softdepend: [WorldEdit]