How to Use an Iterator on an ArrayList in Java

The following example code demonstrates How to Use an Iterator on an ArrayList in Java.

Problem Definition

In order to create an ArrayList of Companies, create a Company class that contains the company_id, company_name, and an ArrayList of Emp objects as its attributes. Display the details of companies using an iterator.

Here’s an example of how to create an ArrayList of Company objects and display the details of each company using an Iterator.

import java.util.*;

class Employee {
  private int id;
  private String name;
  private int age;

  public Employee(int id, String name, int age) {
    this.id = id;
    this.name = name;
    this.age = age;
  }

  public String toString() {
    return "Employee [id=" + id + ", name=" + name + ", age=" + age + "]";
  }
}

class Company {
  private int id;
  private String name;
  private List<Employee> employees;

  public Company(int id, String name) {
    this.id = id;
    this.name = name;
    employees = new ArrayList<>();
  }

  public void addEmployee(Employee employee) {
    employees.add(employee);
  }

  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("Company [id=" + id + ", name=" + name + "]\n");
    for (Employee employee : employees) {
      sb.append("  " + employee + "\n");
    }
    return sb.toString();
  }
}

public class Main {
  public static void main(String[] args) {
    List<Company> companies = new ArrayList<>();
    companies.add(new Company(1, "Google"));
    companies.add(new Company(2, "Apple"));
    companies.add(new Company(3, "Microsoft"));

    companies.get(0).addEmployee(new Employee(101, "John Doe", 30));
    companies.get(0).addEmployee(new Employee(102, "Jane Doe", 25));
    companies.get(1).addEmployee(new Employee(103, "Jim Smith", 35));
    companies.get(2).addEmployee(new Employee(104, "John Smith", 40));
    companies.get(2).addEmployee(new Employee(105, "Jane Smith", 45));

    System.out.println("Using Iterator:");
    Iterator<Company> companyIt = companies.iterator();
    while (companyIt.hasNext()) {
      System.out.println(companyIt.next());
    }
  }
}

In this example, the Company class has three attributes: id, name, and an ArrayList of Employee objects. The Company class has a constructor that initializes the id and name attributes and creates a new ArrayList of Employee objects. The addEmployee method is used to add Employee objects to the employees list. The toString method is overridden to display the details of the company and its employees.

The ArrayList of Company objects is created in the main method and Employee objects are added to each company. The Iterator is then used to traverse the companies list and display the details of each company. The hasNext method is used to check if there are more elements in the list

Problem Definition

Further Reading