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Wednesday 31 July 2013

Multiple Scenario of try , catch and finally in exception handling in java

Following Below multiple scenario question related to try, catch and finally block in exception handling in java
Scenario #1: try throwing an exception; catch and finally both having return statements


public class TestFinally {

/**
* @param args
*/
public static void main(String[] args) {

System.out.println("Inside main method!");
int iReturned = new TestFinally().testMethod();
System.out.println("Returned value of i = " + iReturned);

}

public int testMethod(){

int i = 0;
try{
System.out.println("Inside try block of testMethod!");
i = 100/0;
return i;
}catch(Exception e){
System.out.println("Inside catch block of testMethod!");
i = 200;
return i;
}
finally{
System.out.println("Inside finally block of testMethod!");
i = 300;
return i;
}
}
}


Output: a return (or any control transfer for that matter) in finally always rules!



Inside main method!
Inside try block of testMethod!
Inside catch block of testMethod!
Inside finally block of testMethod!
Returned value of i = 300


Scenarios #2: try having exception-free code and a return; catch and finally both have return




...
try{
System.out.println("Inside try block of testMethod!");
i = 100;
return i;
}catch(Exception e){
System.out.println("Inside catch block of testMethod!");
i = 200;
return i;
}
finally{
System.out.println("Inside finally block of testMethod!");
i = 300;
return i;
}
...


Output: did you get the first one right? This is a cakewalk then. With the same logic that any control transfer in finally always rules we can easily predict the output to be similar to that of Scenario #1 with the only difference that in this case the catch block won't be executed as no exception thrown... all right? Here is the output:



Inside main method!
Inside try block of testMethod!
Inside finally block of testMethod!
Returned value of i = 300


Scenario #3: try having exception; finally doesn't have a return



...
try{
System.out.println("Inside try block of testMethod!");
i = 100/0;
return i;
}catch(Exception e){
System.out.println("Inside catch block of testMethod!");
i = 200;
return i;
}
finally{
System.out.println("Inside finally block of testMethod!");
i = 300;
//return i;
}
...


Output: no return in finally means whatever executable return encountered on the way to finally will be executed once finally completes its execution, so the output would be:



Inside main method!
Inside try block of testMethod!
Inside catch block of testMethod!
Inside finally block of testMethod!
Returned value of i = 200


Scenario #4: try and catch both having exception; finally having a return



...
try{
System.out.println("Inside try block of testMethod!");
i = 100/0;
return i;
}catch(Exception e){
System.out.println("Inside catch block of testMethod!");
i = 200/0;
return i;
}
finally{
System.out.println("Inside finally block of testMethod!");
i = 300;
return i;
}
...


Output: control transfer in finally overrules the exceptions thrown in try/catch, hence the output would be:



Inside main method!
Inside try block of testMethod!
Inside catch block of testMethod!
Inside finally block of testMethod!
Returned value of i = 300


Scenario #5: try and catch both having exception; finally NOT having any return



...
try{
System.out.println("Inside try block of testMethod!");
i = 100/0;
return i;
}catch(Exception e){
System.out.println("Inside catch block of testMethod!");
i = 200/0;
return i;
}
finally{
System.out.println("Inside finally block of testMethod!");
i = 300;
//return i;
}
...


Output: since no return in finally, hence after the execution of the finally block the sheer need to have an executable return statement (which doesn't exist in this case as catch also has an exception) would throw the exception encountered right before the finally execution started, which would be the exception in catch block in our case...right? So, the output would be:



Exception in thread "main" java.lang.ArithmeticException: / by zero
at TestFinally.testMethod(TestFinally.java:24)
at TestFinally.main(TestFinally.java:10)
Inside main method!
Inside try block of testMethod!
Inside catch block of testMethod!
Inside finally block of testMethod!


Scenario #6: try, catch, and finally all three having exceptions



...
try{
System.out.println("Inside try block of testMethod!");
i = 100/0;
return i;
}catch(Exception e){
System.out.println("Inside catch block of testMethod!");
i = 200/0;
return i;
}
finally{
System.out.println("Inside finally block of testMethod!");
i = 300;
return i/0;
}
...


Output: evidently the exception would be thrown, but which one? The one which was encountered last i.e., the one encountered in the finally block. Output would be:



Inside main method!
Inside try block of testMethod!
Inside catch block of testMethod!
Inside finally block of testMethod!
Exception in thread "main" java.lang.ArithmeticException: / by zero
at TestFinally.testMethod(TestFinally.java:30)
at TestFinally.main(TestFinally.java:10)


Scenario #7: try and catch both fine; finally doesn't have any return



...
try{
System.out.println("Inside try block of testMethod!");
i = 100;
return i;
}catch(Exception e){
System.out.println("Inside catch block of testMethod!");
i = 200;
return i;
}
finally{
System.out.println("Inside finally block of testMethod!");
i = 300;
//return i;
}
...


Output: well... first thing first. If try is fine, do we need to even think about catch? A BIG No... right? Okay, so we have try and finally blocks to focus on. Let me first show you the output and then we would discuss if you have any doubts. Here is it:



Inside main method!
Inside try block of testMethod!
Inside finally block of testMethod!
Returned value of i = 100

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