What is the output of the given java code?

Problem statement:
Given java code, what will be the output of it?

1. interface Car {
2. public void startEngine();
3. }
4. class MySuzuki implements Car {
5. public void startEngine() {
6. System.out.println("MySuzuki");
7. }
8. }
9. class MyFerrari implements Car {
10. public void startEngine() {
11. System.out.println("MyFerrari");
12. }
13. }
14. public class OOPSExample {
15. public static void main(String[] args) {
16. MyFerrari obj = new MySuzuki();
17. obj.startEngine();
18. }
19. }

Output:

Compile time error at line 16, due to Type mismatch: cannot convert from MySuzuki to MyFerrari

What is the output of the code?

Problem statement:
Given java code, what will be the output of it?

1. interface Car {
2. public void startEngine();
3. }
4. class MySuzuki implements Car {
5. public void startEngine() {
6. System.out.println("MySuzuki");
7. }
8. }
9. class MyFerrari implements Car {
10. public void startEngine() {
11. System.out.println("MyFerrari");
12. }
13. }
14. public class OOPSExample {
15. public static void main(String[] args) {
16. Car obj = new MySuzuki();
17. obj.startEngine();
18. }
19. }

Output:

MySuzuki

what is the output of the program?

Problem statement:
what is the output of the following code?

1. public class A {
2.     public static void showMe() {
3.         System.out.println("A");
4.     }
5. }
6. class B extends A {
7.     public static void showMe() {
8.         System.out.println("B");
9.     }
10. }
11. class C extends B {
12.     public static void showMe() {
13.         System.out.println("C");
14.     }
15. }
16. class Main {
17.     public static void main(String[] args) {
18.         A a = new B();
19.         a.showMe();
20.         A a1 = new A();
21.         a1.showMe();
22.         B b = new C();
23.         b.showMe();
24.         C c = new C();
25.         c.showMe();
26.     }
27. }

Output:

A

A

B

C

Difference between final, finally and finalize()

final:

• final is a keyword
• final is used to apply restrictions on class, method and variable
• final class cannot be inherited
• final method cannot be overriden
• final variable value cannot be changed

1. class FinalExample {
2. public static void main(String[] args) {
3. final int x = 100;
4. x = 200;// Compile Time Error
5. }
6. }

finally:

• finally is a block
• finally block always execute, whether exception is handled or not
• in one scenario finally block doesn't execute is System.exit(0);

1. class FinallyExample {
2. public static void main(String[] args) {
3. try {
4. int x = 300;
5. } catch (Exception e) {
6. System.out.println(e);
7. } finally {
8. System.out.println("finally block is executed");
9. }
10. }
11. }

finalize():

• finalize() is a method
• finalize is used to perform clean up processing just before object is garbage collected

1. class FinalizeExample {
2. public void finalize() {
3. System.out.println("finalize called");
4. }
5. public static void main(String[] args) {
6. FinalizeExample f1 = new FinalizeExample();
7. FinalizeExample f2 = new FinalizeExample();
8. f1 = null;
9. f2 = null;
10. System.gc();
11. }
12. }

Can we override static method in java?

No ! we cannot override the static methods. Since static method belongs to class level not object level.

class StaticExe1 {
public static void run() {
System.out.println("run of StaticExe1");
}
public  void fly() {
System.out.println("fly of non-static Exe1");
}
}

class StaticExe2 extends StaticExe1 {
public static void run() {
System.out.println("run of StaticExe2");
}
public  void fly() {
System.out.println("fly of non-static Exe2");
}
}
class StaticExe3 extends StaticExe2 {
public static void run() {
System.out.println("run of StaticExe3");
}
public  void fly() {
System.out.println("fly of non-static Exe3");
}
}

public class StaticMethod {

public static void main(String[] args) {

StaticExe2 ex = new StaticExe3();
ex.run();
ex.fly();
}


}
Output:
run of StaticExe2

fly of non-static Exe3

What is the output of the program ? [based on method overriding]

1. class SampleExec1 {
2. void run() {
3. System.out.println("SampleExec1 run");
4. }
5. }
6. class SampleExec2 extends SampleExec1 {
7. void run() {
8. System.out.println("SampleExec2 run");
9. }
10. }
11. public class SampleExecution {
12. public static void main(String[] args) {
13. SampleExec2 ex = new SampleExec1();
14. ex.run();
15. }
16. }

Output: compile time error at line 13. Type mismatch: cannot convert from SampleExec1 to SampleExec2

--------------------------------------------------------------------

1. class SampleExec1 {
2. void run() {
3. System.out.println("SampleExec1 run");
4. }
5. }
6. class SampleExec2 extends SampleExec1 {
7. void run() {
8. System.out.println("SampleExec2 run");
9. }
10. }
11. public class SampleExecution {
12. public static void main(String[] args) {
13. SampleExec2 ex = (SampleExec2 )new SampleExec1();
14. ex.run();
15. }
16. }

Output: 

Exception in thread "main" java.lang.ClassCastException: SampleExec1 cannot be cast to SampleExec2 at SampleExecution.main(SampleExecution .java:14)

--------------------------------------------------------------------

1. class SampleExec1 {
2. void run() {
3. System.out.println("SampleExec1 run");
4. }
5. }
6. class SampleExec2 extends SampleExec1 {
7. void run() {
8. System.out.println("SampleExec2 run");
9. }
10. }
11. public class SampleExecution {
12. public static void main(String[] args) {
13. SampleExec1 ex = new SampleExec2();
14. ex.run();
15. }
16. }

Output: SampleExec2 run

what is cyclic inheritance in java ?

Suppose class A extends class B and class B extends class A. then it will be known as cyclic inheritance.
e.g.

[1]
public class A extends B {
// some code
}
class B extends A {
// some code
}
[2]
public class A extends B {
// some code
}
public class B extends C {
// some code
}
public class C extends A {
// some code
}
[3]
public class A extends A {
// some code
}
error: cyclic inheritance involving.