EASYTUTORGUIDEJava • Java 26

Sealed Classes

Chapter 22 of 60 • beginner to advanced • code example for every topic

5 topics5 code examples10 Q&A

22.1 Declaring Classes 22.2 Fields and State 22.3 Methods 22.4 Constructors 22.5 Encapsulation

22.1 Declaring Classes

This topic teaches Declaring Classes as part of Sealed Classes. Learn the purpose first, then inspect the syntax and test it with small inputs before using it in production.

Code example

class Person { String name; Person(String name){this.name=name;} }
public class Main { public static void main(String[] args){ Person p=new Person("Ana"); System.out.println(p.name); } }

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 Classes. 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.

22.2 Fields and State

This topic teaches Fields and State as part of Sealed Classes. 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) { // Fields and State
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 Fields and State. 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.

22.3 Methods

This topic teaches Methods as part of Sealed Classes. Learn the purpose first, then inspect the syntax and test it with small inputs before using it in production.

Code example

public class Main { static int add(int a,int b){return a+b;} public static void main(String[] args){System.out.println(add(3,4));} }

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 Methods. 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.

22.4 Constructors

This topic teaches Constructors as part of Sealed Classes. Learn the purpose first, then inspect the syntax and test it with small inputs before using it in production.

Code example

class Person { String name; Person(String name){this.name=name;} }
public class Main { public static void main(String[] args){ Person p=new Person("Ana"); System.out.println(p.name); } }

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 Constructors. 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.

22.5 Encapsulation

This topic teaches Encapsulation as part of Sealed Classes. 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) { // Encapsulation
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 Encapsulation. 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.