✅ Using HashMap and ArrayList to Store Test Data in Java
You can combine HashMap and ArrayList in several ways depending on your test design:
1️⃣ A List of Maps (Most Common for Data-Driven Testing)
Each test dataset is a Map, and you store multiple Maps in an ArrayList.
Example Structure
ArrayList<HashMap<String, String>>
✔ Use Case
You have several user records (username, password, role, etc.) and want to iterate through them as separate datasets.
🔹 Example: Storing Multiple Users
import java.util.ArrayList;
import java.util.HashMap;
public class TestDataExample {
public static ArrayList<HashMap<String, String>> getLoginData() {
ArrayList<HashMap<String, String>> dataList = new ArrayList<>();
HashMap<String, String> user1 = new HashMap<>();
user1.put("username", "john123");
user1.put("password", "pass123");
user1.put("role", "admin");
HashMap<String, String> user2 = new HashMap<>();
user2.put("username", "mary007");
user2.put("password", "pass789");
user2.put("role", "user");
dataList.add(user1);
dataList.add(user2);
return dataList;
}
public static void main(String[] args) {
for (HashMap<String, String> user : getLoginData()) {
System.out.println("User Data: " + user);
System.out.println("Username: " + user.get("username"));
System.out.println("Password: " + user.get("password"));
}
}
}
Output
User Data: {username=john123, password=pass123, role=admin}
User Data: {username=mary007, password=pass789, role=user}
Perfect for plugging into TestNG @DataProvider.
🔹 Example: Using This Data in TestNG
@DataProvider(name = "loginData")
public Object[][] loginData() {
ArrayList<HashMap<String, String>> data = TestDataExample.getLoginData();
return new Object[][] {
{ data.get(0) },
{ data.get(1) }
};
}
@Test(dataProvider = "loginData")
public void testLogin(HashMap<String, String> userData) {
System.out.println("Testing login: " + userData.get("username"));
}
2️⃣ A HashMap of Lists (When One Key Has Multiple Values)
Example Structure
HashMap<String, ArrayList<String>>
✔ Use Case
Storing grouped test values like:
multiple email IDs
lists of invalid inputs
dropdown menu options
🔹 Example: Storing Invalid Inputs
import java.util.ArrayList;
import java.util.HashMap;
public class DataBank {
public static HashMap<String, ArrayList<String>> getInvalidData() {
HashMap<String, ArrayList<String>> invalidData = new HashMap<>();
ArrayList<String> badEmails = new ArrayList<>();
badEmails.add("abc");
badEmails.add("test@");
badEmails.add("@domain.com");
ArrayList<String> badPhones = new ArrayList<>();
badPhones.add("1234");
badPhones.add("999999999999");
badPhones.add("phone123");
invalidData.put("emails", badEmails);
invalidData.put("phones", badPhones);
return invalidData;
}
public static void main(String[] args) {
HashMap<String, ArrayList<String>> data = getInvalidData();
System.out.println(data.get("emails"));
System.out.println(data.get("phones"));
}
}
3️⃣ A Map Inside a Map (Nested Structure)
Example Structure
HashMap<String, HashMap<String, String>>
✔ Use Case
Grouping large structured test sets like:
form fields
product details
test environment configs
🔹 Example: Environment Configuration
HashMap<String, HashMap<String, String>> env = new HashMap<>();
HashMap<String, String> dev = new HashMap<>();
dev.put("url", "https://dev.example.com");
dev.put("db", "dev_db");
HashMap<String, String> qa = new HashMap<>();
qa.put("url", "https://qa.example.com");
qa.put("db", "qa_db");
env.put("DEV", dev);
env.put("QA", qa);
System.out.println(env.get("QA").get("url")); // Prints QA URL
4️⃣ ArrayList of Custom Objects (Cleaner Alternative)
Sometimes instead of maps, it’s cleaner to use a POJO class.
Example
class User {
String username;
String password;
String role;
public User(String username, String password, String role) {
this.username = username;
this.password = password;
this.role = role;
}
}
ArrayList<User> users = new ArrayList<>();
users.add(new User("john", "123", "admin"));
✔ Best for large, structured data
✔ More readable than maps
✔ Works beautifully with TestNG
🎯 When to Use What?
Use Case Data Structure Best For
Multiple test records ArrayList<HashMap<...>> Data-driven tests
One key → many values HashMap<String, ArrayList<...>> Invalid data, dropdown items
Nested structured data HashMap<String, HashMap<...>> Environments, configs
Clean, typed objects ArrayList<POJO> Large structured test data
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