o If the superclass method does not declare an exception, subclass overridden method cannot declare the checked exception but it can declare unchecked exception.

• If the superclass method declares an exception

o If the superclass method declares an exception, subclass overridden method can declare same, subclass exception or no exception but cannot declare parent exception.

If the superclass method does not declare an exception

1) Rule: If the superclass method does not declare an exception, subclass overridden method cannot declare the checked exception.

1. import java.io.*; 
2. class Parent{ 
3. void msg(){System.out.println("parent");} 
4. } 
5. 
6. class TestExceptionChild extends Parent{ 
7. void msg()throws IOException{ 
8. System.out.println("TestExceptionChild"); 
9. } 
10. public static void main(String args[]){ 
11. Parent p=new TestExceptionChild(); 
12. p.msg(); 
13. } 
14. }

Output:Compile Time Error

2) Rule: If the superclass method does not declare an exception, subclass overridden method cannot declare the checked exception but can declare unchecked exception.

1. import java.io.*; 
2. class Parent{ 
3. void msg(){System.out.println("parent");} 
4. } 
5. 
6. class TestExceptionChild1 extends Parent{ 
7. void msg()throws ArithmeticException{ 
8. System.out.println("child"); 
9. } 
10. public static void main(String args[]){ 
11. Parent p=new TestExceptionChild1(); 
12. p.msg(); 
13. } 
14. }

Output:child
If the superclass method declares an exception
1) Rule: If the superclass method declares an exception, subclass overridden method can declare same, subclass exception or no exception but cannot declare parent exception.

Example in case subclass overridden method declares parent exception

1. import java.io.*; 
2. class Parent{ 
3. void msg()throws ArithmeticException{System.out.println("parent");} 
4. } 
5. 
6. class TestExceptionChild2 extends Parent{ 
7. void msg()throws Exception{System.out.println("child");} 
8. 
9. public static void main(String args[]){ 
10. Parent p=new TestExceptionChild2(); 
11. try{ 
12. p.msg(); 
13. }catch(Exception e){} 
14. } 
15. }

Output:Compile Time Error

Example in case subclass overridden method declares same exception

1. import java.io.*; 
2. class Parent{ 
3. void msg()throws Exception{System.out.println("parent");} 
4. } 
5. 
6. class TestExceptionChild3 extends Parent{ 
7. void msg()throws Exception{System.out.println("child");} 
8. 
9. public static void main(String args[]){ 
10. Parent p=new TestExceptionChild3(); 
11. try{ 
12. p.msg(); 
13. }catch(Exception e){} 
14. } 
15. }

Output:child

Example in case subclass overridden method declares subclass exception

1. import java.io.*; 
2. class Parent{ 
3. void msg()throws Exception{System.out.println("parent");} 
4. } 
5. 
6. class TestExceptionChild4 extends Parent{ 
7. void msg()throws ArithmeticException{System.out.println("child");} 
8. 
9. public static void main(String args[]){ 
10. Parent p=new TestExceptionChild4(); 
11. try{ 
12. p.msg(); 
13. }catch(Exception e){} 
14. } 
15. }

Output:child

Example in case subclass overridden method declares no exception

1. import java.io.*; 
2. class Parent{ 
3. void msg()throws Exception{System.out.println("parent");} 
4. } 
5. 
6. class TestExceptionChild5 extends Parent{ 
7. void msg(){System.out.println("child");} 
8. 
9. public static void main(String args[]){ 
10. Parent p=new TestExceptionChild5(); 
11. try{ 
12. p.msg(); 
13. }catch(Exception e){} 
14. } 
15. }

Output:child

Difference between throw and throws in Java

There are many differences between throw and throws keywords. A list of differences between throw and throws are given below:

No.	throw	throws
1)	Java throw keyword is used to explicitly throw an exception.	Java throws keyword is used to declare an exception.
2)	Checked exception cannot be propagated using throw only.	Checked exception can be propagated with throws.
3)	Throw is followed by an instance.	Throws is followed by class.
4)	Throw is used within the method.	Throws is used with the method signature.
5)	You cannot throw multiple exceptions.	You can declare multiple exceptions e.g. public void method()throws IOException,SQLException.

Java throw example

1. void m(){ 
2. throw new ArithmeticException("sorry"); 
3. }

Java throws example

1. void m()throws ArithmeticException{ 
2. //method code 
3. }

Java throw and throws example

1. void m()throws ArithmeticException{ 
2. throw new ArithmeticException("sorry"); 
3. }

Difference between final, finally and finalize

No.	final	finally	finalize
1)	Final is used to apply restrictions on class, method and variable. Final class can’t be inherited, final method can’t be overridden and final variable value can’t be changed.	Finally is used to place important code, it will be executed whether exception is handled or not.	Finalize is used to perform clean up processing just before object is garbage collected.
2)	Final is a keyword.	Finally is a block.	Finalize is a method.

Java final example

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

Java finally example

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

Java finalize example

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

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