how to run TraversalExample.java example

[Tingting Cui]

when i try to run TraversalExample.java example and create the graph like this 

it give me error like this

Exception in thread "main" java.lang.NullPointerException

at setupneo4j.TraversalExample.<init>(TraversalExample.java:23)

at setupneo4j.TraversalExample.main(TraversalExample.java:33)

what is the problems here.

public static void main( String[] args )

    {

        

    TraversalExample op = new TraversalExample( db );

        op.shutdownGraph();

    }

    public void shutdownGraph()

    {

        try

        {

            if ( db != null )

            {

                db.shutdown();

            }

        }

        finally

        {

            db = null;

        }

    }

    public Node createTheGraph()

    {

        try ( Transaction tx = db.beginTx() )

        {

            // START SNIPPET: createGraph

            Node A = db.createNode();

            Node B = db.createNode();

            Node C = db.createNode();

            Node D = db.createNode();

    

            A.createRelationshipTo( C, Rels.KNOWS );

            C.createRelationshipTo( D, Rels.KNOWS );

            A.createRelationshipTo( B, Rels.KNOWS);

            B.createRelationshipTo( C, Rels.KNOWS );

            // END SNIPPET: createGraph

            A.setProperty( "name", "A" );

            B.setProperty( "name", "B" );

            C.setProperty( "name", "C" );

            D.setProperty( "name", "D" );

            tx.success();

            return A;

        }

    }

[Anders Nawroth]

Hi!

Did you initialize the db field?

Something like 

db  = new GraphDatabaseFactory().newEmbeddedDatabase( "path/to/db" );

/anders

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[TC]

why cannot i use this way to create node use int array

                int[] newnode=new int[10];

        for(int i=0; i<newnode.length; i++){

        Node newnode[i]=db.createNode();

        }

       

        newnode[1].createRelationshipTo(newnode[2], Rels.KNOWS );

[Michael Hunger]

You should use a Node[] array

Perhaps you want to rather use cypher from another language than writing Java code?

Sent from mobile device

[TC]

hi, i use node array. i think it is fine now. but i have another question here.

public static void main( String[] args )

    {

    final String DB_PATH = "target/neo4j-hello-db";

    GraphDatabaseService db = new GraphDatabaseFactory().newEmbeddedDatabase(DB_PATH);

    TraversalExample op = new TraversalExample( db );

    op.createTheGraph();

        op.shutdownGraph();

    }

    public void shutdownGraph()

    {

        try

        {

            if ( db != null )

            {

                db.shutdown();

            }

        }

        finally

        {

            db = null;

        }

    }

    public Node createTheGraph()

    {

        try ( Transaction tx = db.beginTx() )

        {

            // START SNIPPET: createGraph

       

        Node[] newno=new Node[5];

        for(int i=0; i<newno.length; i++){

        newno[i]=db.createNode();

        }

       

        newno[1].createRelationshipTo(newno[2], Rels.KNOWS );

        newno[1].createRelationshipTo(newno[4], Rels.KNOWS );

        newno[4].createRelationshipTo(newno[2], Rels.KNOWS );

        newno[2].createRelationshipTo(newno[3], Rels.KNOWS );

        System.out.println(knowsLikesTraverser(newno[1]));

       

            return newno[1];

        }

    }

    public String knowsLikesTraverser( Node node )

    {

        String output = "";

        // START SNIPPET: knowslikestraverser

        for ( Path position : db.traversalDescription()

                .depthFirst()

                .relationships( Rels.KNOWS )

                

                .evaluator( Evaluators.toDepth( 5 ) )

                .traverse( node ) )

        {

            output += position + "\n";

        }

        // END SNIPPET: knowslikestraverser

        return output;

    }

while it give me output like this.

(4350)

(4350)--[KNOWS,8328]-->(4351)

(4350)--[KNOWS,8328]-->(4351)--[KNOWS,8331]-->(4352)

(4350)--[KNOWS,8328]-->(4351)<--[KNOWS,8330]--(4353)

why it give the number like 4350 and 8328? this big number. it supposed to be just 0-4. Thanks.

if i just want to node to traversal forward and backward separately.  Right now the traversal is mixed together.

Thanks.