Flow control in try catch finally in Java

In this article, we’ll explore all the possible combinations of try-catch-finally which may happen whenever an exception is raised and how the control flow occurs in each of the given cases. 

1. Control flow in try-catch clause OR try-catch-finally clause
   • Case 1: Exception occurs in try block and handled in catch block
   • Case 2: Exception occurs in try-block is not handled in catch block
   • Case 3: Exception doesn’t occur in try-block
2. try-finally clause
   • Case 1: Exception occurs in try block
   • Case 2: Exception doesn’t occur in try-block

Control flow in try-catch OR try-catch-finally

1. Exception occurs in try block and handled in catch block: If a statement in try block raised an exception, then the rest of the try block doesn’t execute and control passes to the corresponding catch block. After executing the catch block, the control will be transferred to finally block(if present) and then the rest program will be executed. 

• Control flow in try-catch:

Java

// Java program to demonstrate
// control flow of try-catch clause
// when exception occur in try block
// and handled in catch block
class GFG
{
    public static void main (String[] args)
    {

        // array of size 4.
        int[] arr = new int[4];
        try
        {
            int i = arr[4];

            // this statement will never execute
            // as exception is raised by above statement
            System.out.println("Inside try block");
        }
        catch(ArrayIndexOutOfBoundsException ex)
        {
            System.out.println("Exception caught in Catch block");
        }

        // rest program will be executed
        System.out.println("Outside try-catch clause");
    }
}

Output

Exception caught in Catch block
Outside try-catch clause

• Control flow in try-catch-finally clause :

Java

// Java program to demonstrate
// control flow of try-catch-finally clause
// when exception occur in try block
// and handled in catch block
class GFG
{
    public static void main (String[] args)
    {

        // array of size 4.
        int[] arr = new int[4];

        try
        {
            int i = arr[4];

            // this statement will never execute
            // as exception is raised by above statement
            System.out.println("Inside try block");
        }

        catch(ArrayIndexOutOfBoundsException ex)
        {
            System.out.println("Exception caught in catch block");
        }

        finally
        {
            System.out.println("finally block executed");
        }

        // rest program will be executed
        System.out.println("Outside try-catch-finally clause");
    }
}

Output

Exception caught in catch block
finally block executed
Outside try-catch-finally clause

2. Exception occurred in try-block is not handled in catch block: In this case, the default handling mechanism is followed. If finally block is present, it will be executed followed by the default handling mechanism. 

• try-catch clause :

Java

// Java program to demonstrate
// control flow of try-catch clause
// when exception occurs in try block
// but not handled in catch block
class GFG
{
    public static void main (String[] args)
    {

        // array of size 4.
        int[] arr = new int[4];
        try
        {
            int i = arr[4];

            // this statement will never execute
            // as exception is raised by above statement
            System.out.println("Inside try block");
        }

        // not a appropriate handler
        catch(NullPointerException ex)
        {
            System.out.println("Exception has been caught");
        }

        // rest program will not execute
        System.out.println("Outside try-catch clause");
    }
}

Run Time Error: 

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
    at GFG.main(GFG.java:12)

• try-catch-finally clause :

Java

// Java program to demonstrate
// control flow of try-catch-finally clause
// when exception occur in try block
// but not handled in catch block
class GFG
{
    public static void main (String[] args)
    {

        // array of size 4.
        int[] arr = new int[4];

        try
        {
            int i = arr[4];

            // this statement will never execute
            // as exception is raised by above statement
            System.out.println("Inside try block");
        }

        // not a appropriate handler
        catch(NullPointerException ex)
        {
            System.out.println("Exception has been caught");
        }

        finally
        {
            System.out.println("finally block executed");
        }

        // rest program will not execute
        System.out.println("Outside try-catch-finally clause");
    }
}

Output : 

finally block executed

Run Time error: 

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
    at GFG.main(GFG.java:12)

3. Exception doesn’t occur in try-block: In this case catch block never runs as they are only meant to be run when an exception occurs. finally block(if present) will be executed followed by rest of the program. 

• try-catch clause :

Java

// Java program to demonstrate try-catch
// when an exception doesn't occurred in try block
class GFG
{
    public static void main (String[] args)
    {

        try
        {

            String str = "123";

            int num = Integer.parseInt(str);

            // this statement will execute
            // as no any exception is raised by above statement
            System.out.println("Inside try block");

        }

        catch(NumberFormatException ex)
        {

            System.out.println("catch block executed...");

        }

        System.out.println("Outside try-catch clause");
    }
}

Output

Inside try block
Outside try-catch clause

• try-catch-finally clause 

Java

// Java program to demonstrate try-catch-finally
// when exception doesn't occurred in try block
class GFG
{
    public static void main (String[] args)
    {

    try
    {

        String str = "123";

        int num = Integer.parseInt(str);

        // this statement will execute
        // as no any exception is raised by above statement
        System.out.println("try block fully executed");

    }

    catch(NumberFormatException ex)
    {

        System.out.println("catch block executed...");

    }

    finally
    {
        System.out.println("finally block executed");
    }

    System.out.println("Outside try-catch-finally clause");
    }
}

Output

try block fully executed
finally block executed
Outside try-catch-finally clause

Control flow in try-finally

In this case, no matter whether an exception occurs in try-block or not finally will always be executed. But control flow will depend on whether an exception has occurred in the try block or not. 

1. Exception raised: If an exception has occurred in the try block then the control flow will be finally block followed by the default exception handling mechanism.

Java

// Java program to demonstrate
// control flow of try-finally clause
// when exception occur in try block
class GFG
{
    public static void main (String[] args)
    {

        // array of size 4.
        int[] arr = new int[4];
        try
        {
            int i = arr[4];

            // this statement will never execute
            // as exception is raised by above statement
            System.out.println("Inside try block");
        }

        finally
        {
            System.out.println("finally block executed");
        }

        // rest program will not execute
        System.out.println("Outside try-finally clause");
    }
}

Output : 

finally block executed
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
    at GFG.main(GFG.java:11)

2. Exception not raised: If an exception does not occur in the try block then the control flow will be finally block followed by the rest of the program

Java

// Java program to demonstrate
// control flow of try-finally clause
// when exception doesn't occur in try block
class GFG
{
    public static void main (String[] args)
    {

        try
        {
            String str = "123";

            int num = Integer.parseInt(str);

            // this statement will execute
            // as no any exception is raised by above statement
            System.out.println("Inside try block");
        }

        finally
        {
            System.out.println("finally block executed");
        }

        // rest program will be executed
        System.out.println("Outside try-finally clause");
    }
}

Output

Inside try block
finally block executed
Outside try-finally clause

This article is contributed by Gaurav Miglani. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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