30.1 Declaring Interfaces
This topic teaches Declaring Interfaces as part of Method References and Functional Interfaces. Learn the purpose first, then inspect the syntax and test it with small inputs before using it in production.
Code example
public class Main { public static void main(String[] args) { // Declaring Interfaces
System.out.println("Java example"); } }Step-by-step explanation
- Identify the values, objects, tables, or resources used by the example.
- Read each statement in execution order.
- Predict what the program or query should produce.
- Run it in a safe local/test environment.
- Change one input and explain the new result.
Expected output/result
You should see a small result that demonstrates Declaring Interfaces. Exact formatting can differ by runtime, client, database state, operating system, or tool version.
Common mistakes
Watch for invalid input, unchecked errors, incorrect type assumptions, missing cleanup, unsafe permissions, injection risks, or code/query logic that handles only the happy path.
Practice exercise
Rebuild this example with your own data. Add one edge case, predict the result before running it, and explain why the final result is correct.
30.2 Implementing Interfaces
This topic teaches Implementing Interfaces as part of Method References and Functional Interfaces. Learn the purpose first, then inspect the syntax and test it with small inputs before using it in production.
Code example
public class Main { public static void main(String[] args) { // Implementing Interfaces
System.out.println("Java example"); } }Step-by-step explanation
- Identify the values, objects, tables, or resources used by the example.
- Read each statement in execution order.
- Predict what the program or query should produce.
- Run it in a safe local/test environment.
- Change one input and explain the new result.
Expected output/result
You should see a small result that demonstrates Implementing Interfaces. Exact formatting can differ by runtime, client, database state, operating system, or tool version.
Common mistakes
Watch for invalid input, unchecked errors, incorrect type assumptions, missing cleanup, unsafe permissions, injection risks, or code/query logic that handles only the happy path.
Practice exercise
Rebuild this example with your own data. Add one edge case, predict the result before running it, and explain why the final result is correct.
30.3 Multiple Contracts
This topic teaches Multiple Contracts as part of Method References and Functional Interfaces. Learn the purpose first, then inspect the syntax and test it with small inputs before using it in production.
Code example
public class Main { public static void main(String[] args) { // Multiple Contracts
System.out.println("Java example"); } }Step-by-step explanation
- Identify the values, objects, tables, or resources used by the example.
- Read each statement in execution order.
- Predict what the program or query should produce.
- Run it in a safe local/test environment.
- Change one input and explain the new result.
Expected output/result
You should see a small result that demonstrates Multiple Contracts. Exact formatting can differ by runtime, client, database state, operating system, or tool version.
Common mistakes
Watch for invalid input, unchecked errors, incorrect type assumptions, missing cleanup, unsafe permissions, injection risks, or code/query logic that handles only the happy path.
Practice exercise
Rebuild this example with your own data. Add one edge case, predict the result before running it, and explain why the final result is correct.
30.4 Default/Static Members
This topic teaches Default/Static Members as part of Method References and Functional Interfaces. Learn the purpose first, then inspect the syntax and test it with small inputs before using it in production.
Code example
public class Main { public static void main(String[] args) { // Default/Static Members
System.out.println("Java example"); } }Step-by-step explanation
- Identify the values, objects, tables, or resources used by the example.
- Read each statement in execution order.
- Predict what the program or query should produce.
- Run it in a safe local/test environment.
- Change one input and explain the new result.
Expected output/result
You should see a small result that demonstrates Default/Static Members. Exact formatting can differ by runtime, client, database state, operating system, or tool version.
Common mistakes
Watch for invalid input, unchecked errors, incorrect type assumptions, missing cleanup, unsafe permissions, injection risks, or code/query logic that handles only the happy path.
Practice exercise
Rebuild this example with your own data. Add one edge case, predict the result before running it, and explain why the final result is correct.
30.5 Interface Design
This topic teaches Interface Design as part of Method References and Functional Interfaces. Learn the purpose first, then inspect the syntax and test it with small inputs before using it in production.
Code example
public class Main { public static void main(String[] args) { // Interface Design
System.out.println("Java example"); } }Step-by-step explanation
- Identify the values, objects, tables, or resources used by the example.
- Read each statement in execution order.
- Predict what the program or query should produce.
- Run it in a safe local/test environment.
- Change one input and explain the new result.
Expected output/result
You should see a small result that demonstrates Interface Design. Exact formatting can differ by runtime, client, database state, operating system, or tool version.
Common mistakes
Watch for invalid input, unchecked errors, incorrect type assumptions, missing cleanup, unsafe permissions, injection risks, or code/query logic that handles only the happy path.
Practice exercise
Rebuild this example with your own data. Add one edge case, predict the result before running it, and explain why the final result is correct.
10 Questions & Answers
1. What should you know about Declaring Interfaces?
Know the purpose, syntax, inputs, result, edge cases, common errors, and the security or performance concern where applicable.
2. What should you know about Implementing Interfaces?
Know the purpose, syntax, inputs, result, edge cases, common errors, and the security or performance concern where applicable.
3. What should you know about Multiple Contracts?
Know the purpose, syntax, inputs, result, edge cases, common errors, and the security or performance concern where applicable.
4. What should you know about Default/Static Members?
Know the purpose, syntax, inputs, result, edge cases, common errors, and the security or performance concern where applicable.
5. What should you know about Interface Design?
Know the purpose, syntax, inputs, result, edge cases, common errors, and the security or performance concern where applicable.
6. What should you know about Declaring Interfaces?
Know the purpose, syntax, inputs, result, edge cases, common errors, and the security or performance concern where applicable.
7. What should you know about Implementing Interfaces?
Know the purpose, syntax, inputs, result, edge cases, common errors, and the security or performance concern where applicable.
8. What should you know about Multiple Contracts?
Know the purpose, syntax, inputs, result, edge cases, common errors, and the security or performance concern where applicable.
9. What should you know about Default/Static Members?
Know the purpose, syntax, inputs, result, edge cases, common errors, and the security or performance concern where applicable.
10. What should you know about Interface Design?
Know the purpose, syntax, inputs, result, edge cases, common errors, and the security or performance concern where applicable.