help manually roting vertices

hi there guys, firstly id like to say hello to all as this is my first post here Cheesy

so i have just recently gotten into 3d development in java and so far i have picked up pretty fast, the hardest part was probably setting up my environment, but as i have programed in ruby for a while i picked up java pretty fast as it is object orientated, any way enough of that to the issue!

so i am currently trying to rotate vertices manually, i know i can use the glRotate method to achieve rotation, but this is so i can use logical functions later to detect collision etc, in this case i am constructing a box,i have managed to sort of apply the rotation manually, but it seems to go a little crazy, it rotates, but doesnt rotate to the right angle, so here is my code that manages the box and drawing of it:

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package com.game.base.uncatogorized.Graphics;

import static org.lwjgl.opengl.GL11.*;

public class Cube {

   public float xScale, yScale, zScale;
   
   public Cube(float xScale, float yScale, float zScale) {
      
      this.xScale = xScale;
      this.yScale = yScale;
      this.zScale = zScale;
      
   }
   
   public void draw(float x, float y, float z, float rotation) {
      float x1, y1, z1, rx, rz;
      
      glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
      glPushMatrix(); 
      {
         glTranslatef(0, 0, 0);
         glColor3f(1,0,0);  
         glBegin(GL_QUADS);
         {
            
            //FRONT FACE
            //BOTTOM LEFT
            x1 = x - ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //BOTTOM RIGHT
            x1 = x + ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP RIGHT
            x1 = x + ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP LEFT
            x1 = x - ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            
            //RIGHT FACE
            //BOTTOM LEFT
            x1 = x - ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //BOTTOM RIGHT
            x1 = x - ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP RIGHT
            x1 = x - ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP LEFT
            x1 = x - ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            
            //BACK FACE
            //BOTTOM LEFT
            x1 = x - ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //BOTTOM RIGHT
            x1 = x + ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP RIGHT
            x1 = x + ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP LEFT
            x1 = x - ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            
            //LEFT FACE
            //BOTTOM LEFT
            x1 = x + ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //BOTTOM RIGHT
            x1 = x + ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP RIGHT
            x1 = x + ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP LEFT
            x1 = x + ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            
            //TOP FACE
            //BOTTOM LEFT
            x1 = x - ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //BOTTOM RIGHT
            x1 = x + ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP RIGHT
            x1 = x + ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP LEFT
            x1 = x - ((1 * xScale) / 2);
            y1 = y + ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            
            //BOTTOM FACE
            //BOTTOM LEFT
            x1 = x - ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //BOTTOM RIGHT
            x1 = x + ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z - ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP RIGHT
            x1 = x + ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
            //TOP LEFT
            x1 = x - ((1 * xScale) / 2);
            y1 = y - ((1 * yScale) / 2);
            z1 = z + ((1 * zScale) / 2);
            rx = (float) ((z1 * Math.sin(rotation)) + (x1 * Math.cos(rotation)));
            rz = (float) ((z1 * Math.cos(rotation)) - (x1 * Math.sin(rotation)));
            glVertex3f(rx, y1, rz);
         }
         glEnd();
         
      }
      glPopMatrix();
      glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
      glColor3f(1,1,1);     
   }
   
}

i am currently only trying to rotate on the x and z, as you can see i am drawing the boxes in line mode, as that space will just represent impassable space, the reason i need it to rotate is so it rotates correctly with the object that it is bound around, ie. a character, then this box will act as the characters collider

also on the matter is this a good way to go about generating a collision area? i know about the physics library jbullet but that is a bit of an overhaul for what i require, anyway let me know if anyone knows how i can solve this