Please read the instruction from these pictures.
You can use these codes below.
game.java (The codes of the picture below) :
https://drive.google.com/file/d/1vggE2dDlb9d7PdE1vB6_AIa2bxytc3Um/view?usp=sharing
Game.java :
https://drive.google.com/file/d/1Ax_n-lW65wCPXgelFctKGnx93i1KNFdc/view?usp=sharing
GameObject.java :
https://drive.google.com/file/d/1M3nbQUVt9FjY_aco5YtAN_g-moXgfYhk/view?usp=sharing
Enemy.java :
https://drive.google.com/file/d/12ZmBwbsH5ltgSI18gWcZJX5DHwgEqYoi/view?usp=sharing
Player.java
https://drive.google.com/file/d/1Kn1PAXE3NONPyYPaeHBBH3gCdjcwaN6l/view?usp=sharing