Fix checkstyle errors

src/Server/src/main/java/greenify/server/data/model/User.java

@@ -7,16 +7,11 @@ import lombok.Data;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Objects;
+import java.util.ArrayList;
+import java.util.Collection;
 
-import javax.persistence.ElementCollection;
-import javax.persistence.Entity;
-import javax.persistence.GeneratedValue;
-import javax.persistence.GenerationType;
-import javax.persistence.Id;
-import javax.persistence.Table;
-import java.util.*;
-import java.util.logging.Logger;
 import javax.persistence.*;
+
 import javax.validation.constraints.NotNull;
 
 @Entity
@@ -27,7 +22,6 @@ public class User {
     @Id
     @NotNull
     @GeneratedValue(strategy = GenerationType.AUTO)
-//    @Column(name = "id")
     private Long id;
 
     @NotNull
@@ -118,6 +112,10 @@ public class User {
         return (ArrayList<User>)this.friends;
     }
 
+    /**
+     * Adds a friend to the friendslist of the user.
+     * @param user the friend you want to add.
+     */
     public void addFriend(User user) {
         if (user.equals(this)) {
             throw new ApplicationException("Cannot add yourself as a friend");
@@ -143,6 +141,10 @@ public class User {
                 + this.password + ")";
     }
 
+    /**
+     * Returns the name and score of the friends in JSON. Needed for the leaderboard.
+     * @return a JSON object of the friendlist with only names and scores.
+     */
     public String friendsToString(){
         String result = "friends=[";
         for (User u : friends) {

src/Server/src/test/java/greenify/server/service/UserServiceTest.java

@@ -49,7 +49,8 @@ public class UserServiceTest {
                 .thenReturn(alex);
         User lola = new User(2L, "lola", "password");
         when(userRepository.findByName(lola.getName()))
-                .thenReturn(lola);    }
+                .thenReturn(lola);
+    }
 
     @Test
     public void validLoginTest() {