Is there any way to create the instance of an abstract class ?

1. public class MyMain{
2. public static void main(String[] args) { // start
3. MyAbstractClass exe = new MyAbstractClass() {
4. @Override
5. void run() {
6. System.out.println("run of abstract class");
7. }
8. };
9. System.out.println(exe.x);
10. exe.run();
11. } // end
12. }
13. 
    
14. abstract class MyAbstractClass {
15. int x = 10;
16. abstract void run();
17. }

Output: 

10

run of abstract class

Note: Yes ! using anonymous class we can create the instance of an abstract class.

Can we create the object of an abstract class ?

1. abstract public class MyAbstractExe {
2. MyAbstractExe exe = new MyAbstractExe();
3. }

No ! we can not create the object / instance of an abstract class. Compiler will give an error at line 2 saying cannot instantiate the type MyAbstractExe 

Can a class inherit from one abstract class ?

1. public class MyAbstractExe2 extends MyAbstractExe1
2. {
3. @Override
4. void run() {
5. System.out.println("run");
6. }
7. }
8. 
   
9. abstract class MyAbstractExe3 {
10. abstract void run();
11. void test() {
12. System.out.println("test of MyAbstractExe3 !!");
13. }
14. }
15. 
    
16. abstract class MyAbstractExe1 {
17. abstract void run();
18. void test() {
19. System.out.println("test of MyAbstractExe1 !!");
20. }
21. }

Yes! we can inherit a class from one abstract class. compiler will not give error.

Can a class inherit from multiple abstract class ?

1. public class MyAbstractExe2 extends MyAbstractExe1, MyAbstractExe3
2. {
3. @Override
4. void run() {
5. System.out.println("run");
6. }
7. }
8. 
   
9. abstract class MyAbstractExe3 {
10. abstract void run();
11. void test() {
12. System.out.println("test of MyAbstractExe3 !!");
13. }
14. }
15. 
    
16. abstract class MyAbstractExe1 {
17. abstract void run();
18. void test() {
19. System.out.println("test of MyAbstractExe1 !!");
20. }
21. }

No ! we can not inherit a class from multiple abstract class. Syntax error by compiler at line 1

Can we have an abstract class with both abstract and concrete method ?

1. abstract class MyAbstractExe {
2. int x = 10;
3. abstract void run();
4. void test() {
5. System.out.println("yes we can have an abstract class with concrete method !!");
6. }
7. }

Yes ! we can have an abstract class with both abstract & concrete method. there is no error.

Can we have an abstract class with concrete method ?

1. abstract class MyAbstractExe {
2. int x = 10;
3. void test() {
4. System.out.println("yes we can have an abstract class with concrete method !!");
5. }
6. }

Yes ! we can have an abstract class with concrete method !! There is no error.

Ca we have an abstract class without abstract method ?

1. abstract class MyAbstractExe {
2. int x = 10;
3. }

Yes ! we can have an abstract class without abstract method. There will not be any error.

Can we have a constructor in an abstract class ?

1. abstract class MyAbstractExe {
2. MyAbstractExe() {
3. System.out.println("yes we can have constructor in abstract class");
4. }
5. }

Yes ! we can have a constructor and there is no error.