Try to upgrade to Java 8. I hope enough people are using it.

core/src/main/java/com/github/games647/fastlogin/core/AuthStorage.java

@@ -18,13 +18,13 @@ public class AuthStorage {
 
     private static final String PREMIUM_TABLE = "premium";
 
-    private final FastLoginCore core;
+    private final FastLoginCore<?> core;
     private final HikariDataSource dataSource;
 
     //a try to fix https://www.spigotmc.org/threads/fastlogin.101192/page-26#post-1874647
     private final Calendar calendar = Calendar.getInstance(Locale.US);
 
-    public AuthStorage(FastLoginCore core, String driver, String host, int port, String databasePath
+    public AuthStorage(FastLoginCore<?> core, String driver, String host, int port, String databasePath
             , String user, String pass) {
         this.core = core;
 

core/src/main/java/com/github/games647/fastlogin/core/BalancedSSLFactory.java

@@ -7,6 +7,7 @@ import java.net.UnknownHostException;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import javax.net.ssl.SSLSocketFactory;
 
@@ -17,9 +18,7 @@ public class BalancedSSLFactory extends SSLSocketFactory {
     //in order to be thread-safe
     private final List<InetAddress> localAddresses;
 
-    private final Object lock = new Object();
-
-    private int id;
+    private AtomicInteger id;
 
     public BalancedSSLFactory(SSLSocketFactory oldFactory, Set<InetAddress> localAddresses) {
         this.oldFactory = oldFactory;
@@ -65,16 +64,7 @@ public class BalancedSSLFactory extends SSLSocketFactory {
     }
 
     private InetAddress getNextLocalAddress() {
-        int next;
-        synchronized (lock) {
-            next = id;
-            id++;
-            if (next == Integer.MAX_VALUE) {
-                id = 0;
-            }
-        }
-
-        int index = next % localAddresses.size();
+        int index = id.incrementAndGet() % localAddresses.size();
         return localAddresses.get(index);
     }
 }

core/src/main/java/com/github/games647/fastlogin/core/CompatibleCacheBuilder.java

@@ -26,10 +26,10 @@ public class CompatibleCacheBuilder<K, V> {
      * @return A new cache builder.
      */
     public static <K, V> CompatibleCacheBuilder<K, V> newBuilder() {
-        return new CompatibleCacheBuilder<K, V>();
+        return new CompatibleCacheBuilder<>();
     }
 
-    private CacheBuilder<K, V> builder;
+    private final CacheBuilder<K, V> builder;
     
     @SuppressWarnings("unchecked")
     private CompatibleCacheBuilder() {

core/src/main/java/com/github/games647/fastlogin/core/hooks/DefaultPasswordGenerator.java

@@ -4,9 +4,9 @@ import java.util.Random;
 
 public class DefaultPasswordGenerator<T> implements PasswordGenerator<T> {
 
-    private final Random random = new Random();
     private static final char[] PASSWORD_CHARACTERS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
             .toCharArray();
+    private final Random random = new Random();
 
     @Override
     public String getRandomPassword(T player) {

core/src/main/java/com/github/games647/fastlogin/core/shared/JoinManagement.java

@@ -8,10 +8,10 @@ import java.util.logging.Level;
 
 public abstract class JoinManagement<T, S extends LoginSource> {
 
-    protected final FastLoginCore core;
+    protected final FastLoginCore<T> core;
     protected final AuthPlugin<T> authHook;
 
-    public JoinManagement(FastLoginCore core, AuthPlugin<T> authHook) {
+    public JoinManagement(FastLoginCore<T> core, AuthPlugin<T> authHook) {
         this.core = core;
         this.authHook = authHook;
     }
@@ -62,8 +62,7 @@ public abstract class JoinManagement<T, S extends LoginSource> {
         }
     }
 
-    private boolean checkPremiumName(String username, S source, PlayerProfile profile)
-            throws Exception {
+    private boolean checkPremiumName(String username, S source, PlayerProfile profile) throws Exception {
         if (core.getSharedConfig().get("autoRegister", false)
                 && (authHook == null || !authHook.isRegistered(username))) {
             core.getLogger().log(Level.FINER, "Player {0} uses a premium username", username);

core/src/main/java/com/github/games647/fastlogin/core/shared/MojangApiConnector.java

@@ -1,6 +1,8 @@
 package com.github.games647.fastlogin.core.shared;
 
 import com.github.games647.fastlogin.core.BalancedSSLFactory;
+import com.google.common.collect.Sets;
+
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStreamReader;
@@ -8,7 +10,6 @@ import java.net.HttpURLConnection;
 import java.net.InetAddress;
 import java.net.URL;
 import java.net.UnknownHostException;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.UUID;
@@ -56,7 +57,7 @@ public abstract class MojangApiConnector {
         if (localAddresses.isEmpty()) {
             this.sslFactory = null;
         } else {
-            Set<InetAddress> addresses = new HashSet<>();
+            Set<InetAddress> addresses = Sets.newHashSet();
             for (String localAddress : localAddresses) {
                 try {
                     InetAddress address = InetAddress.getByName(localAddress);