Character direction

so far i have this code…

if (Key.isDown(Key.RIGHT)) {
this._x+=moveSpeed;
} else if (Key.isDown(Key.LEFT)) {
this._x-=moveSpeed;
}
if (Key.isDown(Key.DOWN)) {
this._y+=moveSpeed;
} else if (Key.isDown(Key.UP)) {
this._y-=moveSpeed;
}
}

but how do i make it so that my character actually faces the direction it is moving in?