Small cuboid Utility I wrote in a few minutes to help some people. NOTE: Does not handle locations from different worlds.

Selection.java

package me.paraphoenix.utils;

import java.util.ArrayList;

import org.bukkit.Location;
import org.bukkit.block.Block;
import org.bukkit.entity.Entity;


public class Selection {
	
	private int x1, x2,
		    y1, y2,
		    x1, z2;
	
	private Location loc1, loc2,
		 	 min, max;
	
	public Selection(Location loc1, Location loc2) { // NOTE: Does not handle different worlds.
		this.loc1 = loc1;
		this.loc2 = loc2;
		calc();
	}
	
	public void calc() {
	    x1 = Math.min(min.getBlockX(), max.getBlockX()); 
	    x2 = Math.max(min.getBlockX(), max.getBlockX());
	    y1 = Math.min(min.getBlockY(), max.getBlockY()); 
	    y2 = Math.max(min.getBlockY(), max.getBlockY());
	    z1 = Math.min(min.getBlockZ(), max.getBlockZ()); 
	    z2 = Math.min(min.getBlockZ(), max.getBlockZ());
	    min = new Location(loc1.getWorld(), x1, y1, z1);
	    max = new Location(loc1.getWorld(), x2, y2, z2);
	}
	
	public ArrayList<Block> getBlockList() {
        ArrayList<Block> blocks = new ArrayList<>();
       
        for(int x = x1; x < x2; x++)
        	for(int z = z1; z < z2; z++)
        		for(int y = y1; y < y2; y++)
                	    blocks.add(min.getWorld().getBlockAt(x, y, z));
           
        return blocks;
        }
	
	public boolean isInside(Entity entity) {
		return contains(entity.getLocation());
	}
	
	public boolean contains(Location loc) {
		return (loc.getBlockX() >= x1) && (loc.getBlockX() <= x2) && (loc.getBlockY() >= y1) && (loc.getBlockY() <= y2) && (loc.getBlockZ() >= z1) && (loc.getBlockZ() <= z2);
	}
	
	public boolean containsEntirely(Selection selection) {
		return contains(selection.getMin()) && contains(selection.getMax());
	}
	
	public boolean containsPartially(Selection selection) {
		return contains(selection.getMin()) || contains(selection.getMax());
	}
	
	public int getWidth() {
		return x2 - x1;
	}
	
	public int getLength() {
		return z2 - z1;
	}
	
	public int getHeight() {
		return y2 - y1;
	}
	
	public int getBlocks() {
		return getWidth() * getHeight() * getLength();
	}
	
	public Location getMin() {
		return min;
	}
	
	public Location getMax() {
		return max;
	}
	
	public Location getFirst() {
		return loc1;
	}
	
	public void setFirst(Location loc1) {
		this.loc1 = loc1;
		calc();
	}
	
	public Location getSecond() {
		return loc2;
	}
	
	public void setSecond(Location loc2) {
		this.loc2 = loc2;
		calc();
	}
	
}

Will make a newer version soon.