i have a associationmodel class which is pretty easy:  package login;  import java.util.List;  public class AssociationModel {     private String AssociationName;     private List&lt;UserModel&gt; UserList;  public AssociationModel(String name){     this.AssociationName = name; }  public void RegisterUser(UserModel user){     UserList.add(user); } public List&lt;UserModel&gt; getUsers(){     return UserList; } public String getName(){     return AssociationName; } }   Furthemore i have another class which has an java.util.list of AssociationModel´s  If i want to add AssociationModel´s to the AssociationList of the other class i get a stracktrace          while (SearchAssociationsResult.next()){             //AssociationList.add(new AssociationModel(SearchAssociationsResult.getString("ASSOCIATION_NAME")));             AssociationModel l_association = new AssociationModel(SearchAssociationsResult.getString("ASSOCIATION_NAME"));             AssociationList.add(l_association);             System.out.println(l_association.getName());         }     Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException     at login.AssociationController.CreateAssociations(AssociationController.java:35)     at login.AssociationController.&lt;init&gt;(AssociationController.java:16)     at login.LoginController.LoginAttempt(LoginController.java:48)     at login.LoginView$1.actionPerformed(LoginView.java:52)     at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)     at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)     at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)     at javax.swing.DefaultButtonModel.setPressed(Unknown Source)     at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)     at java.awt.Component.processMouseEvent(Unknown Source)     at javax.swing.JComponent.processMouseEvent(Unknown Source)     at java.awt.Component.processEvent(Unknown Source)     at java.awt.Container.processEvent(Unknown Source)     at java.awt.Component.dispatchEventImpl(Unknown Source)     at java.awt.Container.dispatchEventImpl(Unknown Source)     at java.awt.Component.dispatchEvent(Unknown Source)     at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)     at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)     at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)     at java.awt.Container.dispatchEventImpl(Unknown Source)     at java.awt.Window.dispatchEventImpl(Unknown Source)     at java.awt.Component.dispatchEvent(Unknown Source)     at java.awt.EventQueue.dispatchEventImpl(Unknown Source)     at java.awt.EventQueue.access$500(Unknown Source)     at java.awt.EventQueue$3.run(Unknown Source)     at java.awt.EventQueue$3.run(Unknown Source)     at java.security.AccessController.doPrivileged(Native Method)     at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)     at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)     at java.awt.EventQueue$4.run(Unknown Source)     at java.awt.EventQueue$4.run(Unknown Source)     at java.security.AccessController.doPrivileged(Native Method)     at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)     at java.awt.EventQueue.dispatchEvent(Unknown Source)     at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)     at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)     at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)     at java.awt.EventDispatchThread.pumpEvents(Unknown Source)     at java.awt.EventDispatchThread.pumpEvents(Unknown Source)     at java.awt.EventDispatchThread.run(Unknown Source)   I am sure its a pretty stupid mistake...
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