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POhow should I solve my NullPointerException?
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  1. POhow should I solve my NullPointerException?
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    copied!<p>I really don not know what else to do,I have searched every where,tried anything but could not solve my problem.I created a neo4j graph database and created an index on name property of nodes through localhost:7474(visually),now I want to get the node numbers by searching their name property index,but I get nullpointerexception error,I know this is because of existing a null value,and I know where is this from,but I can not solve it.</p> <p>this is the code:</p> <pre><code>package graph_traversing; import org.neo4j.graphdb.GraphDatabaseService; import org.neo4j.graphdb.factory.GraphDatabaseFactory; import org.neo4j.graphdb.index.Index; import org.neo4j.graphdb.Node; import org.neo4j.graphdb.Relationship; import org.neo4j.graphdb.RelationshipType; import org.neo4j.graphdb.Transaction; import org.neo4j.graphdb.index.IndexHits; import org.neo4j.graphdb.index.IndexManager; public class search_string extends javax.swing.JFrame { public search_string() {initComponents(); } @SuppressWarnings("unchecked") private static enum RelTypes implements RelationshipType { INCLUDES } private static final String DB_PATH = "C:\\Users\\fereshteh\\Downloads\\Compressed\\neo4j-community-1.9.4\\DB"; GraphDatabaseService db = new GraphDatabaseFactory().newEmbeddedDatabase( DB_PATH ); IndexManager nodeindex = db.index(); Index&lt;Node&gt; names = nodeindex.forNodes( "name" ); String [] str; Node [] nodes;Relationship rel; IndexHits&lt;Node&gt; hits; String find; // &lt;editor-fold defaultstate="collapsed" desc="Generated Code"&gt; private void initComponents() { jLabel1 = new javax.swing.JLabel(); search_txb = new javax.swing.JTextField(); search_btn = new javax.swing.JButton(); setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); jLabel1.setText(" Enter The Word Please"); search_btn.setText("Search"); search_btn.addActionListener(new java.awt.event.ActionListener() { public void actionPerformed(java.awt.event.ActionEvent evt) { search_btnActionPerformed(evt); } }); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); getContentPane().setLayout(layout); layout.setHorizontalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGap(46, 46, 46) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addComponent(search_btn) .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 147, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(search_txb, javax.swing.GroupLayout.PREFERRED_SIZE, 289, javax.swing.GroupLayout.PREFERRED_SIZE)) .addContainerGap(65, Short.MAX_VALUE)) ); layout.setVerticalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGap(38, 38, 38) .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 36, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(39, 39, 39) .addComponent(search_txb, javax.swing.GroupLayout.PREFERRED_SIZE, 43, javax.swing.GroupLayout.PREFERRED_SIZE) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 71, Short.MAX_VALUE) .addComponent(search_btn) .addGap(50, 50, 50)) ); pack(); }// &lt;/editor-fold&gt; private void search_btnActionPerformed(java.awt.event.ActionEvent evt) { str=search_txb.getText().split(" "); for(int i=0;i&lt;str.length;++i) { find=str[i]; hits = names.get("name", find); System.out.println(hits); nodes [i] = hits.getSingle(); // nodes [i]= nodeIndex.get( "name", find ).getSingle(); System.out.println(nodes[i]); } String s ="hi"; for(int i=0;i&lt;nodes.length;++i) { rel= (Relationship) nodes[i].getRelationships(); for(int j=i+1;j&lt;nodes.length;++j) { s=rel.toString(); } } System.out.println(s); } public static void main(String args[]) { java.awt.EventQueue.invokeLater(new Runnable() {public void run() {new search_string().setVisible(true);} }); } // Variables declaration - do not modify private javax.swing.JLabel jLabel1; private javax.swing.JButton search_btn; private javax.swing.JTextField search_txb; // End of variables declaration } </code></pre> <p>the error firstly belongs to this line: <code>nodes [i] = hits.getSingle();</code></p> <p>I have changed it and <code>hits = names.get("name", find);</code> to so many other codes,but always get the error.</p> <p>and this is the error:</p> <pre><code>Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at graph_traversing.search_string.search_btnActionPerformed(search_string.java:90) at graph_traversing.search_string.access$000(search_string.java:14) at graph_traversing.search_string$1.actionPerformed(search_string.java:50) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252) at java.awt.Component.processMouseEvent(Component.java:6505) at javax.swing.JComponent.processMouseEvent(JComponent.java:3320) at java.awt.Component.processEvent(Component.java:6270) at java.awt.Container.processEvent(Container.java:2229) at java.awt.Component.dispatchEventImpl(Component.java:4861) at java.awt.Container.dispatchEventImpl(Container.java:2287) at java.awt.Component.dispatchEvent(Component.java:4687) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422) at java.awt.Container.dispatchEventImpl(Container.java:2273) at java.awt.Window.dispatchEventImpl(Window.java:2719) at java.awt.Component.dispatchEvent(Component.java:4687) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735) at java.awt.EventQueue.access$200(EventQueue.java:103) at java.awt.EventQueue$3.run(EventQueue.java:694) at java.awt.EventQueue$3.run(EventQueue.java:692) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87) at java.awt.EventQueue$4.run(EventQueue.java:708) at java.awt.EventQueue$4.run(EventQueue.java:706) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) at java.awt.EventQueue.dispatchEvent(EventQueue.java:705) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138) at java.awt.EventDispatchThread.run(EventDispatchThread.java:91) </code></pre> <p>I have put <code>System.out.println(hits);</code> to understand whether hits is null or not,but I see in output hits have <code>org.neo4j.index.impl.lucene.LuceneIndex$1@481f3834</code> value(is this the right output?I expected to get the nodes).</p> <p>this is java api,and this will be really really kind of you if you help me,please,I have got dizziness.</p>
 

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