Return in try catch finally in java

Java finally block when return statement is encountered

In my last tutorial, we discussed about finally block, which is used with a try block and always execute whether exception occurs or not. Here we will see few examples to understand the behaviour of finally block when a return statement is encountered in try block.

Lets see this code snippet, What do you think? Will finally would execute even if there is a return statement in try block as well as in catch block?

try < //try block . return success; >catch (Exception ex) < //catch block . return failure; >finally

The answer is yes. finally block will execute. The only case where it will not execute is when it encounters System.exit().

Finally: Example with return statement

class FinallyDemo < public static int myMethod() < try < //try block return 0; >finally < //finally System.out.println("Inside Finally block"); >> public static void main(String args[]) < System.out.println(FinallyDemo.myMethod()); >>

Does finally block Override the values returned by try-catch block?

Yes. Finally block overrides the value returned by try and catch blocks, lets take an example to understand this:

public static int myTestingFuncn() < try< . return 5; >finally < . return 19; >>

This program would return value 19 since the value returned by try has been overridden by finally.

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4. Valid Cases with correct return statements :

4.1 Write return statement after completion of try-catch-finally blocks; that is just before end of method

Reason:

• This is valid case because after try-catch-finally block execution, method returns value
• Also, it can be seen as 2 independent entities with,
• 1 st being try-catch-finally block
• 2 nd is return statement after try-catch-finally block

4.2 Write return statement inside finally-block only; but there shouldn’t be any statement after finally-block

Reason:

• whether any exception is raised or NOT from try-block
• and its corresponding exception is being handled or NOT in the catch-block
• finally-block will always be executed irrespective of the program’s outcome
• except in one scenario when System.exit(0); is invoked explicitly
• Error-scenario : any statement after finally block will result in compile-time error stating “Unreachable code”

4.3 Write return statement inside both try-block & catch-block; there is no compulsion to write return inside finally-block and this completely optional (Case 6)

Reason:

• Whenever try-block executes successfully, then it can return value for this method
• Also, if any exception is raised from try-block then its corresponding exception will be caught in the catch-block
• And from catch-block also, it can return value for this method
• Error-scenario : any statement after finally block in this example, will result in compile-time error stating “Unreachable code”

4.4.1 Write return statement inside try-block & at the end of method; that is just before end of method

Reason:

• Whenever try-block executes successfully, then it can always return value for this method
• But if any exception is raised & it is handled in the corresponding catch-block –> return statement at the end of method will be executed and returns the value for this method after executing finally-block
• Error-scenario : any statement after return statement at the end of method, will result in compile-time error stating “Unreachable code”

4.4.2 Write return statement inside both try-block & finally-block; but no statement after finally block

Reason:

• Whenever try-block executes successfully, then it can always return value for this method
• But if any exception is raised & it is handled in the corresponding catch-block –> return statement inside finally-block will return value for this method (after executing any statement inside finally-block before encountering return statement)
• Error-scenario : any statement after return statement (i.e.; finally-block in this case) will result in compile-time error stating “Unreachable code”

4.4.3 Write return statement inside both try-block & finally-block; but no statement after finally block (no catch block for this case)

Reason:

• This case is very similar to Case 4.B but it has got no catch block in try-catch-finally blocks sequence
• So, whenever try-block executes successfully, then it can always return value for this method from try-block
• But if any exception is raised then it is NOT handled as there is no catch-block for this case
• So, whenever exception is raised then JVM checks for handler-code up in the runtime stack & finally-block gets executed to return value (after executing any statement inside finally-block before encountering return statement)
• Error-scenario : any statement after return statement (i.e.; finally-block in this case) will result in compile-time error stating “Unreachable code”

4.5.1 Write return statement inside catch-block & at the end of method; that is just before end of method

Reason:

• Whenever try-block executes successfully, then it can always return value from end of method
• If any exception is raised from try-block then it get caught in the corresponding catch-block and catch-block can also return value
• But if any exception is raised & it is handled in the corresponding catch-block –> return statement at the end of method will be executed and returns value for this method after executing finally-block
• Error-scenario : any statement after return statement at the end of method, will result in compile-time error stating “Unreachable code”

4.5.2 Write return statement inside both catch-block & finally-block; but no statement after finally-block

Reason:

• Whenever try-block executes successfully, then it can always return value from finally-block
• If any exception is raised from try-block then it is get caught in the corresponding catch-block and catch-block can also returns value
• But if any exception is raised & it is handled in the corresponding catch-block –> return statement inside finally-block will return value for this method (after executing any statement inside finally-block before encountering return statement)
• Error-scenario : any statement after return statement (i.e.; finally-block) will result in compile-time error stating “Unreachable code”

4.6 Write return statement inside try-block & catch-block & finally-block; but return value from try-block or catch-block will be overridden by return statement in the finally-block

Reason:

• Whenever try-block executes successfully, then it can return value for this method from try-block
• Similarly, if any exception is raised then exception gets caught in the catch-block & it can also return value (from catch-block)
• Since, we have finally-block returning value therefore returning value from try-blockorcatch-block will be overridden by return statement in the finally-block
• Because, on all cases finally-block gets executed irrespective of exception is raised or NOT from try-block and it is handled or NOT inside catch-block.
• Therefore, overrides any return value from try-block or catch-block
• This is called overridden case
• Error-scenario : any statement after finally block in this example, will result in compile-time error stating “Unreachable code”

4.7 Conclusion for Valid case:

• Above 9 examples are valid cases to write return statement;
• except these 9 example mentioned in the above cases, all other cases results in compile-time error
• following examples depicts few of those cases

Let us see some compile-time error for invalid cases

5. Invalid Cases with incorrect return statements :

1. returns value from try-block only
2. returns value from catch-block only
3. returns value from try-catch-finally blocks; but contains some statements after finally-block
4. returns value from finally-block only; but contains some statements after finally block

5.1 returns value from try-block only

• Compile-time error: This method must return a result of type int

5.2 returns value from catch-block only

• Compile-time error: This method must return a result of type int

5.3 returns value from try-catch-finally blocks; but contains some statements after finally-block

5.4 returns value from finally-block only; but contains some statements after finally block

5.5 Conclusion for Invalid cases:

• Any code present after finally-block will results compile-time error stating “Unreachable code“
• Similarly, any code after return statement will results compile-time error stating “Unreachable code“

6. Final Conclusion:

Out of all possible valid cases,

• If a method contains a finally-block
• then finally-block will always gets executed
• irrespective of any valid combination used in the program

In the next article, we will see detail example on return statement with finally block

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• Java – Exception Handling
• Java – Exception Hierarchy
• Java – 5 important keywords in Java Exception handling
• Java – Runtime mechanism, what happens when exception is thrown ?
• Java – Checked Exception v/s Unchecked Exception
• Java – Exception propagation
• Java – try-catch block
• Java – finally block
• Java – try with multiple catch blocks
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• Java – Returning value from method having try-catch-finally blocks
• Java – return statement with finally block
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• Java 7 – try with resources
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References:

• https://docs.oracle.com/javase/tutorial/essential/exceptions/finally.html
• https://docs.oracle.com/javase/tutorial/essential/exceptions/try.html
• https://docs.oracle.com/javase/tutorial/essential/exceptions/catch.html
• https://docs.oracle.com/javase/tutorial/essential/exceptions/
• https://docs.oracle.com/javase/7/docs/api/java/lang/Exception.html
• https://docs.oracle.com/javase/7/docs/api/java/lang/Error.html
• https://docs.oracle.com/javase/specs/jls/se7/html/jls-11.html
• https://docs.oracle.com/javase/7/docs/api/java/lang/ArithmeticException.html
• https://docs.oracle.com/javase/7/docs/api/java/lang/NullPointerException.html
• http://docs.oracle.com/javase/7/docs/api/java/lang/ArrayIndexOutOfBoundsException.html
• http://www.oracle.com/technetwork/java/effective-exceptions-092345.html
• http://otfried.org/courses/cs206/slides/slides-stackframes.pdf

Happy Coding !!
Happy Learning !!

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