4.9.1 Writing a Custom PGX Algorithm

A PGX algorithm is a regular .java file with a single class definition that is annotated with @GraphAlgorithm. For example:

import oracle.pgx.algorithm.annotations.GraphAlgorithm;

@GraphAlgorithm
public class MyAlgorithm {
    ...
}

A PGX algorithm class must contain exactly one public method which will be used as entry point. The class may contain any number of private methods.

For example:

import oracle.pgx.algorithm.PgxGraph;
import oracle.pgx.algorithm.VertexProperty;
import oracle.pgx.algorithm.annotations.GraphAlgorithm;
import oracle.pgx.algorithm.annotations.Out;

@GraphAlgorithm
public class MyAlgorithm {
    public int myAlgorithm(PgxGraph g, @Out VertexProperty<Integer> distance) {
        System.out.println("My first PGX Algorithm program!");

        return 42;
    }
}

As with normal Java methods, a PGX algorithm method only supports primitive data types as return values (an integer in this example). More interesting is the @Out annotation, which marks the vertex property distance as output parameter. The caller passes output parameters by reference. This way, the caller has a reference to the modified property after the algorithm terminates.

• Collections
  
• Iteration
  
• Reductions