如何解决线程中的异常；AWT-EventQueue-0“；java.lang.NullPointerException

我得到这个错误：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at graph_traversing.search_string.search_btnActionPerformed(search_string.java:84)
    at graph_traversing.search_string.access$000(search_string.java:12)
    at graph_traversing.search_string$1.actionPerformed(search_string.java:45)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
    at javax.swing.AbstractButton$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)

尝试运行此代码时：

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;


public class search_string extends javax.swing.JFrame
{
    public search_string() { initComponents(); }
    @SuppressWarnings("unchecked")

    private static enum RelTypes implements RelationshipType
    {
        INCLUDES
    }

    GraphDatabaseService db;  
    private static final String DB_PATH = "C:\\Users\\fereshteh\\Downloads\\Compressed\\neo4j-community-1.9.4\\DB";
    private static Index<Node> nodeIndex;
    String [] str;
    Node [] nodes;
    Relationship rel;    
    String find;

    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    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();
    }// </editor-fold>                        

    private void search_btnActionPerformed(java.awt.event.ActionEvent evt) {                                           

        str=search_txb.toString().split(" ");
        db = new GraphDatabaseFactory().newEmbeddedDatabase( DB_PATH );
        for(int i=0;i<str.length;++i)
        {
            find=str[i];
            nodes [i]= nodeIndex.get( "name", find ).getSingle();
        }
        String s = "hi";
        for(int i=0; i<nodes.length; ++i)
        {
            rel= (Relationship) nodes[i].getRelationships();
            for(int j=i+1;j<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                   
}

我试图解决它，通过改变它几次，但无法解决

---

如果您能帮助我正确运行代码，我将不胜感激。

有四个变量/值可以是

null

：

节点

，

节点索引

，

查找

，

节点索引.get（“name”，find）

。其中一个导致错误。请尝试通过调试应用程序来找出错误的原因。顺便说一下，您的代码片段没有显示

节点的初始化

和

节点索引

您忘记了吗？我不知道如何初始化它们，这会导致错误吗？如果

节点索引

在尝试调用

get

方法时为

null

，这将导致

null点异常

。由于我不知道

neo4j

库，很遗憾，我无法帮助您创建对象。请您帮助我查找空值，我应该如何查找？例如，您可以添加

System.out.println（nodeIndex）

在相关行之前检查

nodeIndex

的值（对于其他变量和值，反之亦然）。

nodes [i]= nodeIndex.get( "name", find ).getSingle();