Added documentation for wrapper class

src/main/java/de/b00tload/tools/lastfmtospotifyplaylist/util/SpotifyCredentials.java

@@ -5,30 +5,53 @@ import java.io.Serializable;
 import java.time.Clock;
 import java.time.LocalDateTime;
 
+/**
+ * A wrapper class for <code>se.michaelthelin.spotify.model_objects.credentials.AuthorizationCodeCredentials</code>. Implements checking validity of access token.
+ */
 public class SpotifyCredentials implements Serializable {
 
     private final AuthorizationCodeCredentials cred;
     private final LocalDateTime validUntil;
 
+    /**
+     * Initializes the class
+     * @param cred The <code>AuthorizationCodeCredentials</code> to be saved. Recommended for use with recently (last few seconds) generated Credentials
+     */
     public SpotifyCredentials(AuthorizationCodeCredentials cred){
         this.cred = cred;
         this.validUntil = LocalDateTime.now(Clock.systemDefaultZone()).plusSeconds(cred.getExpiresIn());
     }
 
+    /**
+     * Get the access token. It becomes invalid after a certain period of time. Check validity with <code>isValid()</code>.
+     * @return An access token that can be provided in subsequent calls, for example to Spotify Web API services.
+     */
     public String getAccessToken(){
         return cred.getAccessToken();
     }
 
+    /**
+     * Get the refresh token. This token can be sent to the Spotify Accounts service in place of an authorization code to retrieve a new access token.
+     * @return A token that can be sent to the Spotify Accounts service in place of an access token.
+     */
     public String getRefreshToken(){
         return cred.getRefreshToken();
     }
 
+    /**
+     * Returns a <code>LocalDateTime</code> which represents the latest point in time when the access token is still valid.
+     * @return A <code>LocalDateTime</code> representing the latest point in time of access token validity
+     */
     public LocalDateTime getValidUntil(){
         return validUntil;
     }
 
+    /**
+     * Checks whether the saved access token is still valid for use in calls, for example to the Spotify Web API services.
+     * @return true if the access token is still valid for use, false if not.
+     */
     public boolean isValid(){
-        return LocalDateTime.now(Clock.systemDefaultZone()).isBefore(validUntil);
+        return LocalDateTime.now(Clock.systemDefaultZone()).isBefore(getValidUntil());
     }
 
 }