update applyPrize method.

src/Tank.java

 import javax.imageio.ImageIO;
+import javax.swing.*;
+import java.awt.*;
 import java.awt.image.BufferedImage;
 import java.io.File;
 import java.io.IOException;
 
+/**
+ * this class keeps tank info
+ * @author narges salehi & sepehr tavakoli
+ * @version 1.1
+ * @since July 21 2020
+ */
 public class Tank {
 
+    //x of tank
     int x;
+    //y of tank
     int y;
+    //rotate amount of tank
     double rotateAmount;
+    //icon of tank
     BufferedImage icon;
-    Bullet bullet;
     GameState state;
-    boolean alive;
+    //keep current prize
     String prize;
+    //keep  current health value
     int Health;
+    //Below fields check expiration of each prize
+    int shieldCounter;
+    int laserCounter;
     boolean bulletEffect;
     boolean laser;
     boolean bullet2;
     boolean bullet3;
-    int shieldCounter;
-    int laserCounter;
+    //check if tank is alive or not
+    boolean alive;
+    int prizeExpiration=0;
 
+
+    /**
+     * create a new tank with given value
+     * @param path of icon of tank
+     * @param x of tank
+     * @param y of tank
+     * @param rotateAmount of tank
+     */
     public Tank(String path, int x, int y, double rotateAmount) {
+        //set default value
         prize = "empty";
         Health = Controller.tankHealth;
+        //set Counter of expiration time of each prize
         shieldCounter = 0;
         laserCounter = 0;
         try {
@@ -38,47 +64,78 @@ public class Tank {
 
     }
 
+    /**
+     * @return icon of tank
+     */
     public BufferedImage getIcon() {
         return icon;
     }
 
+    /**
+     * @return  x of tank
+     */
+
     public int getX() {
         return x;
     }
 
+    /**
+     * @return y of tank
+     */
     public int getY() {
         return y;
     }
 
+    /**
+     * @return state of tank - GameState
+     */
     public GameState getState() {
         return state;
     }
 
+    /**
+     * @return Health value of tank
+     */
     public int getHealth() {
         return Health;
     }
 
+    /**
+     *
+     * @param healthDamage to revalue health of tank
+     */
     public void setHealth(int healthDamage) {
         Health -=  healthDamage;
         if (Health <= 0) Health = 0;
     }
 
-    public String getPrize() {
+    /**
+     * @return current prize
+     */
+    public String getPrize() throws IOException {
         return prize;
     }
 
+    /**
+     * @param prize to set for tank
+     */
     public void setPrize(String prize) {
         this.prize = prize;
     }
 
+    /**
+     * method apply each prize features
+     */
     public void applyPrize() {
+        //check if tank has a prize now
         if (!prize.equals("empty")) {
             if (prize.equals("life")) {
                 Health += 10;
-            }
                 if (Health > 100) {
                     Health = 100;
                 }
+                prize="empty";
+            }
             if (prize.equals("shield")) {
                 if (shieldCounter < 150) {
                     bulletEffect = true;
@@ -86,6 +143,7 @@ public class Tank {
                 } else {
                     shieldCounter = 160;
                     bulletEffect = false;
+                    prize="empty";
                 }
             }
             if (prize.equals("bullet2")) {
@@ -104,9 +162,10 @@ public class Tank {
                     Controller.bulletSpeed = 9;
                     laserCounter++;
                 } else {
-                    laserCounter = 130;
+                    laserCounter = 0;
                     Controller.laser = false;
                     Controller.bulletSpeed = 4;
+                    prize="empty";
                 }
             }
         }