SpriteBatch Switching textures

/** Flushes the batch. */
    public void flush () {
        flushes++;
        buffer.flip();
        MESH.setVertices(buffer);
        lastTexture.bind();
        MESH.draw();
        buffer.clear();
        RenderUtil.unbindTextures();
    }

    /** Begins the SpriteBatch. */
    public void begin () {
        if (rendering) {
            new IllegalStateException("You have to SpriteBatch.end() before calling begin again!").printStackTrace();
        }
        flushes = 0;
        rendering = true;
        shader.bind();
        shader.setUniformMat4f("projection", camera.getCombined());
        shader.setUniformVec4("color", color);
    }

    /** Ends the SpriteBatch, also flushes it. */
    public void end () {
        if (!rendering) {
            new IllegalStateException("You've to SpriteBatch.begin before ending the spritebatch").printStackTrace();
        }
        rendering = false;
        flush();
        RenderUtil.unbindShaders();
        RenderUtil.unbindTextures();
    }

    /** Switches the textures and flushes the old one.
     * @param t */
    private void switchTextures (Texture t) {
        if (lastTexture != null) {
            flush();
        }
        lastTexture = t;
    }