Tidied up a little.

- (Mostly) automatically reformatted code using IntelliJ IDEA to match the Google Style Guide (as documented in CONTRIBUTING.md).
  - 2 space indent, where it wasn't already.
  - Line wrap at 100 characters, where it wasn't already.
  - Wildcard imports were replaced with explicit imports.
  - Unused imports were removed.
  - Annotations were put onto their own line, and additional lines added for readability where necessary.
  - Braces were added to if-statements that didn't already have them.
- Also made some minor edits, e.g. as suggested by IntelliJ IDEA (e.g. public --> private).

This will help with getting the code into shape before style conformance is required as per issue sendgrid#472 and pull request sendgrid#496.

See also:
- https://github.com/google/google-java-format
- https://plugins.jetbrains.com/plugin/8527-google-java-format
- https://github.com/google/styleguide/blob/gh-pages/intellij-java-google-style.xml

src/main/java/com/sendgrid/APICallback.java

@@ -1,19 +1,22 @@
 package com.sendgrid;
 
 /**
- * An interface describing a callback mechanism for the
- * asynchronous, rate limit aware API connection.
+ * An interface describing a callback mechanism for the asynchronous, rate limit aware API
+ * connection.
  */
 public interface APICallback {
-    /**
-     * Callback method in case of an error.
-     * @param ex the error that was thrown.
-     */
-    void error(Exception ex);
 
-    /**
-     * Callback method in case of a valid response.
-     * @param response the valid response.
-     */
-    void response(Response response);
+  /**
+   * Callback method in case of an error.
+   *
+   * @param ex the error that was thrown.
+   */
+  void error(Exception ex);
+
+  /**
+   * Callback method in case of a valid response.
+   *
+   * @param response the valid response.
+   */
+  void response(Response response);
 }

src/main/java/com/sendgrid/RateLimitException.java

@@ -1,36 +1,40 @@
 package com.sendgrid;
 
 /**
- * An exception thrown when the maximum number of retries
- * have occurred, and the API calls are still rate limited.
+ * An exception thrown when the maximum number of retries have occurred, and the API calls are still
+ * rate limited.
  */
 public class RateLimitException extends Exception {
-    private final Request request;
-    private final int retryCount;
 
-    /**
-     * Construct a new exception.
-     * @param request the originating request object.
-     * @param retryCount the number of times a retry was attempted.
-     */
-    public RateLimitException(Request request, int retryCount) {
-        this.request = request;
-        this.retryCount = retryCount;
-    }
+  private final Request request;
+  private final int retryCount;
 
-    /**
-     * Get the originating request object.
-     * @return the request object.
-     */
-    public Request getRequest() {
-        return this.request;
-    }
+  /**
+   * Construct a new exception.
+   *
+   * @param request the originating request object.
+   * @param retryCount the number of times a retry was attempted.
+   */
+  public RateLimitException(Request request, int retryCount) {
+    this.request = request;
+    this.retryCount = retryCount;
+  }
 
-    /**
-     * Get the number of times the action was attemted.
-     * @return the retry count.
-     */
-    public int getRetryCount() {
-        return this.retryCount;
-    }
+  /**
+   * Get the originating request object.
+   *
+   * @return the request object.
+   */
+  public Request getRequest() {
+    return this.request;
+  }
+
+  /**
+   * Get the number of times the action was attemted.
+   *
+   * @return the retry count.
+   */
+  public int getRetryCount() {
+    return this.retryCount;
+  }
 }

src/main/java/com/sendgrid/SendGrid.java

@@ -3,12 +3,12 @@
 import java.io.IOException;
 import java.util.HashMap;
 import java.util.Map;
-import java.util.concurrent.Executors;
 import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 
 /**
-  * Class Twilio SendGrid allows for quick and easy access to the Twilio SendGrid API.
-  */
+ * The Twilio SendGrid class allows for quick and easy access to the Twilio SendGrid API.
+ */
 public class SendGrid implements SendGridAPI {
 
   private static final String VERSION = "3.0.0";
@@ -43,6 +43,7 @@ public class SendGrid implements SendGridAPI {
 
   /**
    * Construct a new Twilio SendGrid API wrapper.
+   *
    * @param apiKey is your Twilio SendGrid API Key: https://app.sendgrid.com/settings/api_keys
    */
   public SendGrid(String apiKey) {
@@ -52,6 +53,7 @@ public SendGrid(String apiKey) {
 
   /**
    * Construct a new Twilio SendGrid API wrapper.
+   *
    * @param apiKey is your Twilio SendGrid API Key: https://app.sendgrid.com/settings/api_keys
    * @param test is true if you are unit testing
    */
@@ -62,6 +64,7 @@ public SendGrid(String apiKey, Boolean test) {
 
   /**
    * Construct a new Twilio SendGrid API wrapper.
+   *
    * @param apiKey is your Twilio SendGrid API Key: https://app.sendgrid.com/settings/api_keys
    * @param client the Client to use (allows to customize its configuration)
    */
@@ -72,6 +75,7 @@ public SendGrid(String apiKey, Client client) {
 
   /**
    * Initialize the client.
+   *
    * @param apiKey the user's API key.
    */
   public void initializeSendGrid(String apiKey) {
@@ -89,14 +93,16 @@ public void initializeSendGrid(String apiKey) {
 
   /**
    * Retrieve the current library version.
+   *
    * @return the current version.
    */
   public String getLibraryVersion() {
-    return this.VERSION;
+    return VERSION;
   }
 
   /**
    * Get the API version.
+   *
    * @return the current API versioin (v3 by default).
    */
   public String getVersion() {
@@ -105,6 +111,7 @@ public String getVersion() {
 
   /**
    * Set the API version.
+   *
    * @param version the new version.
    */
   public void setVersion(String version) {
@@ -113,6 +120,7 @@ public void setVersion(String version) {
 
   /**
    * Obtain the request headers.
+   *
    * @return the request headers.
    */
   public Map<String, String> getRequestHeaders() {
@@ -121,6 +129,7 @@ public Map<String, String> getRequestHeaders() {
 
   /**
    * Add a new request header.
+   *
    * @param key the header key.
    * @param value the header value.
    * @return the new set of request headers.
@@ -132,6 +141,7 @@ public Map<String, String> addRequestHeader(String key, String value) {
 
   /**
    * Remove a request header.
+   *
    * @param key the header key to remove.
    * @return the new set of request headers.
    */
@@ -142,6 +152,7 @@ public Map<String, String> removeRequestHeader(String key) {
 
   /**
    * Get the Twilio SendGrid host (api.sendgrid.com by default).
+   *
    * @return the Twilio SendGrid host.
    */
   public String getHost() {
@@ -150,15 +161,16 @@ public String getHost() {
 
   /**
    * Set the Twilio SendGrid host.
+   *
    * @param host the new Twilio SendGrid host.
    */
   public void setHost(String host) {
     this.host = host;
   }
 
   /**
-   * Get the maximum number of retries on a rate limit response. 
-   * The default is 5.
+   * Get the maximum number of retries on a rate limit response. The default is 5.
+   *
    * @return the number of retries on a rate limit.
    */
   public int getRateLimitRetry() {
@@ -167,25 +179,26 @@ public int getRateLimitRetry() {
 
   /**
    * Set the maximum number of retries on a rate limit response.
+   *
    * @param rateLimitRetry the maximum retry count.
    */
   public void setRateLimitRetry(int rateLimitRetry) {
     this.rateLimitRetry = rateLimitRetry;
   }
 
   /**
-   * Get the duration of time (in milliseconds) to sleep between
-   * consecutive rate limit retries. The Twilio SendGrid API enforces
-   * the rate limit to the second. The default value is 1.1 seconds.
+   * Get the duration of time (in milliseconds) to sleep between consecutive rate limit retries. The
+   * Twilio SendGrid API enforces the rate limit to the second. The default value is 1.1 seconds.
+   *
    * @return the sleep duration.
    */
   public int getRateLimitSleep() {
     return this.rateLimitSleep;
   }
 
   /**
-   * Set the duration of time (in milliseconds) to sleep between
-   * consecutive rate limit retries.
+   * Set the duration of time (in milliseconds) to sleep between consecutive rate limit retries.
+   *
    * @param rateLimitSleep the sleep duration.
    */
   public void setRateLimitSleep(int rateLimitSleep) {
@@ -194,6 +207,7 @@ public void setRateLimitSleep(int rateLimitSleep) {
 
   /**
    * Impersonate subuser for subsequent requests
+   *
    * @param subuser the subuser to be impersonated
    */
   public void addImpersonateSubuser(String subuser) {
@@ -211,14 +225,16 @@ public void removeImpersonateSubuser() {
 
   /**
    * Get the impersonated subuser or null if empty
+   *
    * @return the impersonated subuser
    */
   public String getImpersonateSubuser() {
-    return this.subuser; 
+    return this.subuser;
   }
 
   /**
    * Makes the call to the Twilio SendGrid API, override this method for testing.
+   *
    * @param request the request to make.
    * @return the response object.
    * @throws IOException in case of a network error.
@@ -229,6 +245,7 @@ public Response makeCall(Request request) throws IOException {
 
   /**
    * Class api sets up the request to the Twilio SendGrid API, this is main interface.
+   *
    * @param request the request object.
    * @return the response object.
    * @throws IOException in case of a network error.
@@ -250,9 +267,9 @@ public Response api(Request request) throws IOException {
   }
 
   /**
-   * Attempt an API call. This method executes the API call asynchronously
-   * on an internal thread pool. If the call is rate limited, the thread
-   * will retry up to the maximum configured time.
+   * Attempt an API call. This method executes the API call asynchronously on an internal thread
+   * pool. If the call is rate limited, the thread will retry up to the maximum configured time.
+   *
    * @param request the API request.
    */
   public void attempt(Request request) {
@@ -267,10 +284,10 @@ public void response(Response r) {
   }
 
   /**
-   * Attempt an API call. This method executes the API call asynchronously
-   * on an internal thread pool. If the call is rate limited, the thread
-   * will retry up to the maximum configured time. The supplied callback
-   * will be called in the event of an error, or a successful response.
+   * Attempt an API call. This method executes the API call asynchronously on an internal thread
+   * pool. If the call is rate limited, the thread will retry up to the maximum configured time. The
+   * supplied callback will be called in the event of an error, or a successful response.
+   *
    * @param request the API request.
    * @param callback the callback.
    */