How to Create Generators in Java

Sheeraz Gul Feb 02, 2024

Java Java Generator

Generators are simple ways to create iterators. It can be described as an object or data which can be iterated over one value at a time.

Java does not provide any built-in functionality for generators like Python, but we can use an iterator to create one.

This tutorial will demonstrate how to create generators in Java.

Use Iterator to Create Generators in Java

Iterators are used to iterate through multidimensional arrays, which means they can perform the functionality of multi-layer loops.

package delftstack;
import java.util.Arrays;
import java.util.Iterator;
public class Java_Generator {
  public static void main(String args[]) {
    Integer[][][] Demo_Array =
        new Integer[][][] {{{1, 2, null, 3}, null, {4}}, null, {{5}, {6}, null, {7}}};

    Iterator<Integer> demo_iterator =
        Arrays.stream(Demo_Array)
            .filter(ab -> ab != null)
            .flatMap(ab
                -> Arrays.stream(ab)
                       .filter(ac -> ac != null)
                       .flatMap(ac -> Arrays.stream(ac).filter(ae -> ae != null)))
            .iterator();

    while (demo_iterator.hasNext()) {
      System.out.println(demo_iterator.next());
    }
  }
}

The code above iterates through a three-dimensional array and prints the values neglecting the null values.

Output:

We can also use the Stream directly and set logic to iterate according to a particular pattern.

package delftstack;
import java.util.Iterator;
import java.util.stream.*;
public class Java_Generator {
  public static void main(String args[]) {
    Iterator<Integer> Demo_Generator =
        Stream.iterate(new Integer[] {1, 2}, demo -> new Integer[] {demo[1], demo[0] + demo[1]})
            .map(demo -> demo[0])
            .iterator();

    // Print the first 10 elements according to the given iterator logic
    for (int x = 0; x < 10; x++) {
      System.out.println(Demo_Generator.next());
    }

    System.out.println("First Iteration for 10 elements is finished here, Now the next 10");

    // Print the first 10 elements according to the given iterator logic
    for (int x = 0; x < 10; x++) {
      System.out.println(Demo_Generator.next());
    }
  }
}

The code above creates a stream with logic to iterate through numbers with only two numbers given in the array.

It generates more numbers according to the logic in the new integer array and map() function, creating a sequence with the following number sum of the previous two numbers.

Output:

1
2
3
5
8
13
21
34
55
89
First Iteration for 10 elements is finished here, Now the next 10
144
233
377
610
987
1597
2584
4181
6765
10946

Author: Sheeraz Gul

Sheeraz is a Doctorate fellow in Computer Science at Northwestern Polytechnical University, Xian, China. He has 7 years of Software Development experience in AI, Web, Database, and Desktop technologies. He writes tutorials in Java, PHP, Python, GoLang, R, etc., to help beginners learn the field of Computer Science.

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