Java try block is used to enclose the code that might throw an exception. It must be used within the method.
If an exception occurs at the particular statement of try block, the rest of the block code will not execute. So, it is recommended not to keeping the code in try block that will not throw an exception.
Java try block must be followed by either catch or finally block.

Syntax of Java try-catch

1. try{ 
2. //code that may throw an exception 
3. }catch(Exception_class_Name ref){}

Syntax of try-finally block

1. try{ 
2. //code that may throw an exception 
3. }finally{}

Java catch block

Java catch block is used to handle the Exception by declaring the type of exception within the parameter. The declared exception must be the parent class exception ( i.e., Exception) or the generated exception type. However, the good approach is to declare the generated type of exception.
The catch block must be used after the try block only. You can use multiple catch block with a single try block.

Problem without exception handling

Let’s try to understand the problem if we don’t use a try-catch block.

Example 1

1. public class TryCatchExample1 { 
2. 
3. public static void main(String[] args) { 
4. 
5. int data=50/0; //may throw exception 
6. 
7. System.out.println("rest of the code"); 
8. 
9. } 
10. 
11. }

Output:

Exception in thread “main” java.lang.ArithmeticException: / by zero
As displayed in the above example, the rest of the code is not executed (in such case, the rest of the code statement is not printed).
There can be 100 lines of code after exception. So all the code after exception will not be executed.

Solution by exception handling

Let’s see the solution of the above problem by a java try-catch block.

Example 2

1. public class TryCatchExample2 { 
2. 
3. public static void main(String[] args) { 
4. try 
5. { 
6. int data=50/0; //may throw exception 
7. } 
8. //handling the exception 
9. catch(ArithmeticException e) 
10. { 
11. System.out.println(e); 
12. } 
13. System.out.println("rest of the code"); 
14. } 
15. 
16. }

Output:
java.lang.ArithmeticException: / by zero

rest of the code
Now, as displayed in the above example, the rest of the code is executed, i.e., the rest of the code statement is printed.

Example 3

In this example, we also kept the code in a try block that will not throw an exception.

1. public class TryCatchExample3 { 
2. 
3. public static void main(String[] args) { 
4. try 
5. { 
6. int data=50/0; //may throw exception 
7. // if exception occurs, the remaining statement will not exceute 
8. System.out.println("rest of the code"); 
9. } 
10. // handling the exception 
11. catch(ArithmeticException e) 
12. { 
13. System.out.println(e); 
14. } 
15. 
16. } 
17. 
18. }

Output:
java.lang.ArithmeticException: / by zero

Here, we can see that if an exception occurs in the try block, the rest of the block code will not execute.

Example 4

Here, we handle the exception using the parent class exception.

1. public class TryCatchExample4 { 
2. 
3. public static void main(String[] args) { 
4. try 
5. { 
6. int data=50/0; //may throw exception 
7. } 
8. // handling the exception by using Exception class 
9. catch(Exception e) 
10. { 
11. System.out.println(e); 
12. } 
13. System.out.println("rest of the code"); 
14. } 
15. 
16. }

Output:
java.lang.ArithmeticException: / by zero

rest of the code

Example 5

Let’s see an example to print a custom message on exception.

1. public class TryCatchExample5 { 
2. 
3. public static void main(String[] args) { 
4. try 
5. { 
6. int data=50/0; //may throw exception 
7. } 
8. // handling the exception 
9. catch(Exception e) 
10. { 
11. // displaying the custom message 
12. System.out.println("Can't divided by zero"); 
13. } 
14. } 
15. 
16. }

Output:
Can’t divided by zero

Example 6

Let’s see an example to resolve the exception in a catch block.

1. public class TryCatchExample6 { 
2. 
3. public static void main(String[] args) { 
4. int i=50; 
5. int j=0; 
6. int data; 
7. try 
8. { 
9. data=i/j; //may throw exception 
10. } 
11. // handling the exception 
12. catch(Exception e) 
13. { 
14. // resolving the exception in catch block 
15. System.out.println(i/(j+2)); 
16. } 
17. } 
18. }

Output:
25

Example 7

In this example, along with try block, we also enclose exception code in a catch block.

1. public class TryCatchExample7 { 
2. 
3. public static void main(String[] args) { 
4. 
5. try 
6. { 
7. int data1=50/0; //may throw exception 
8. 
9. } 
10. // handling the exception 
11. catch(Exception e) 
12. { 
13. // generating the exception in catch block 
14. int data2=50/0; //may throw exception 
15. 
16. } 
17. System.out.println("rest of the code"); 
18. } 
19. }

Output:

Exception in thread “main” java.lang.ArithmeticException: / by zero

Here, we can see that the catch block didn’t contain the exception code. So, enclose exception code within a try block and use catch block only to handle the exceptions.

Example 8

In this example, we handle the generated exception (Arithmetic Exception) with a different type of exception class (ArrayIndexOutOfBoundsException).

1. public class TryCatchExample8 {
2.
3. public static void main(String[] args) {
4. try
5. {
6. int data=50/0; //may throw exception
7.
8. }
9. // try to handle the ArithmeticException using ArrayIndexOutOfBoundsException
10. catch(ArrayIndexOutOfBoundsException e)
11. {
12. System.out.println(e);
13. }
14. System.out.println("rest of the code");
15. }
16.
17. }

Output:
Exception in thread “main” java.lang.ArithmeticException: / by zero

Example 9

Let’s see an example to handle another unchecked exception.

1. public class TryCatchExample9 {
2.
3. public static void main(String[] args) {
4. try
5. {
6. int arr[]= {1,3,5,7};
7. System.out.println(arr[10]); //may throw exception
8. }
9. // handling the array exception
10. catch(ArrayIndexOutOfBoundsException e)
11. {
12. System.out.println(e);
13. }
14. System.out.println("rest of the code");
15. }
16.
17. }

Output:
java.lang.ArrayIndexOutOfBoundsException: 10
rest of the code

Example 10

Let’s see an example to handle checked exception.

1. import java.io.FileNotFoundException;
2. import java.io.PrintWriter;
3.
4. public class TryCatchExample10 {
5.
6. public static void main(String[] args) {
7.
8.
9. PrintWriter pw;
10. try {
11. pw = new PrintWriter("jtp.txt"); //may throw exception
12. pw.println("saved");
13. }
14. // providing the checked exception handler
15. catch (FileNotFoundException e) {
16.
17. System.out.println(e);
18. }
19. System.out.println("File saved successfully");
20. }
21. }

Output:
File saved successfully

Internal working of java try-catch block

java 88

The JVM firstly checks whether the exception is handled or not. If exception is not handled, JVM provides a default exception handler that performs the following tasks:
• Prints out exception description.
• Prints the stack trace (Hierarchy of methods where the exception occurred).
• Causes the program to terminate.
But if exception is handled by the application programmer, normal flow of the application is maintained i.e. rest of the code is executed.

Java catch multiple exceptions

Java Multi-catch block

A try block can be followed by one or more catch blocks. Each catch block must contain a different exception handler. So, if you have to perform different tasks at the occurrence of different exceptions, use java multi-catch block.

Points to remember

• At a time only one exception occurs and at a time only one catch block is executed.
• All catch blocks must be ordered from most specific to most general, i.e. catch for ArithmeticException must come before catch for Exception.

Example 1

Let’s see a simple example of java multi-catch block.

1. public class MultipleCatchBlock1 { 
2. 
3. public static void main(String[] args) { 
4. 
5. try{ 
6. int a[]=new int[5]; 
7. a[5]=30/0; 
8. } 
9. catch(ArithmeticException e) 
10. { 
11. System.out.println("Arithmetic Exception occurs"); 
12. } 
13. catch(ArrayIndexOutOfBoundsException e) 
14. { 
15. System.out.println("ArrayIndexOutOfBounds Exception occurs"); 
16. } 
17. catch(Exception e) 
18. { 
19. System.out.println("Parent Exception occurs"); 
20. } 
21. System.out.println("rest of the code"); 
22. } 
23. }

Output:
Arithmetic Exception occurs
rest of the code

Example 2

1. public class MultipleCatchBlock2 { 
2. 
3. public static void main(String[] args) { 
4. 
5. try{ 
6. int a[]=new int[5]; 
7. 
8. System.out.println(a[10]); 
9. } 
10. catch(ArithmeticException e) 
11. { 
12. System.out.println("Arithmetic Exception occurs"); 
13. } 
14. catch(ArrayIndexOutOfBoundsException e) 
15. { 
16. System.out.println("ArrayIndexOutOfBounds Exception occurs"); 
17. } 
18. catch(Exception e) 
19. { 
20. System.out.println("Parent Exception occurs"); 
21. } 
22. System.out.println("rest of the code"); 
23. } 
24. }

Output:
ArrayIndexOutOfBounds Exception occurs
rest of the code

Example 3

In this example, try block contains two exceptions. But at a time only one exception occurs and its corresponding catch block is invoked.

1. public class MultipleCatchBlock3 { 
2. 
3. public static void main(String[] args) { 
4. 
5. try{ 
6. int a[]=new int[5]; 
7. a[5]=30/0; 
8. System.out.println(a[10]); 
9. } 
10. catch(ArithmeticException e) 
11. { 
12. System.out.println("Arithmetic Exception occurs"); 
13. } 
14. catch(ArrayIndexOutOfBoundsException e) 
15. { 
16. System.out.println("ArrayIndexOutOfBounds Exception occurs"); 
17. } 
18. catch(Exception e) 
19. { 
20. System.out.println("Parent Exception occurs"); 
21. } 
22. System.out.println("rest of the code"); 
23. } 
24. }

Output:
Arithmetic Exception occurs
rest of the code

Example 4

In this example, we generate NullPointerException, but didn’t provide the corresponding exception type. In such case, the catch block containing the parent exception class Exception will invoked.

1. public class MultipleCatchBlock4 { 
2. 
3. public static void main(String[] args) { 
4. 
5. try{ 
6. String s=null; 
7. System.out.println(s.length()); 
8. } 
9. catch(ArithmeticException e) 
10. { 
11. System.out.println("Arithmetic Exception occurs"); 
12. } 
13. catch(ArrayIndexOutOfBoundsException e) 
14. { 
15. System.out.println("ArrayIndexOutOfBounds Exception occurs"); 
16. } 
17. catch(Exception e) 
18. { 
19. System.out.println("Parent Exception occurs"); 
20. } 
21. System.out.println("rest of the code"); 
22. } 
23. }

Output:
Parent Exception occurs
rest of the code

Example 5

Let’s see an example, to handle the exception without maintaining the order of exceptions (i.e. from most specific to most general).

1. class MultipleCatchBlock5{ 
2. public static void main(String args[]){ 
3. try{ 
4. int a[]=new int[5]; 
5. a[5]=30/0; 
6. } 
7. catch(Exception e){System.out.println("common task completed");} 
8. catch(ArithmeticException e){System.out.println("task1 is completed");} 
9. catch(ArrayIndexOutOfBoundsException e){System.out.println("task 2 completed");} 
10. System.out.println("rest of the code..."); 
11. } 
12. }

Output:
Compile-time error
The try block within a try block is known as nested try block in java.

Why use nested try block

Sometimes a situation may arise where a part of a block may cause one error and the entire block itself may cause another error. In such cases, exception handlers have to be nested.

Syntax:

1. ….
2. try
3. {
4. statement 1;
5. statement 2;
6. try
7. {
8. statement 1;
9. statement 2;
10. }
11. catch(Exception e)
12. {
13. }
14. }
15. catch(Exception e)
16. {
17. }
18. ….

Java nested try example

Let’s see a simple example of java nested try block.

1. class Excep6{ 
2. public static void main(String args[]){ 
3. try{ 
4. try{ 
5. System.out.println("going to divide"); 
6. int b =39/0; 
7. }catch(ArithmeticException e){System.out.println(e);} 
8. 
9. try{ 
10. int a[]=new int[5]; 
11. a[5]=4; 
12. }catch(ArrayIndexOutOfBoundsException e){System.out.println(e);} 
13. 
14. System.out.println("other statement); 
15. }catch(Exception e){System.out.println("handeled");} 
16. 
17. System.out.println("normal flow.."); 
18. } 
19. }

Java finally block is a block that is used to execute important code such as closing connection, stream etc.
Java finally block is always executed whether exception is handled or not.
Java finally block follows try or catch block.

java 89

Note: If you don’t handle exception, before terminating the program, JVM executes finally block(if any).

Why use java finally

• Finally block in java can be used to put “cleanup” code such as closing a file, closing connection etc.

Usage of Java finally

Let’s see the different cases where java finally block can be used.
Case 1
Let’s see the java finally example where exception doesn’t occur.

1. class TestFinallyBlock{ 
2. public static void main(String args[]){ 
3. try{ 
4. int data=25/5; 
5. System.out.println(data); 
6. } 
7. catch(NullPointerException e){System.out.println(e);} 
8. finally{System.out.println("finally block is always executed");} 
9. System.out.println("rest of the code..."); 
10. } 
11. }

Output:5
finally block is always executed
rest of the code…

Case 2

Let’s see the java finally example where exception occurs and not handled.

1. class TestFinallyBlock1{ 
2. public static void main(String args[]){ 
3. try{ 
4. int data=25/0; 
5. System.out.println(data); 
6. } 
7. catch(NullPointerException e){System.out.println(e);} 
8. finally{System.out.println("finally block is always executed");} 
9. System.out.println("rest of the code..."); 
10. } 
11. }

Output:finally block is always executed
Exception in thread main java.lang.ArithmeticException:/ by zero

Case 3

Let’s see the java finally example where exception occurs and handled.

1. public class TestFinallyBlock2{ 
2. public static void main(String args[]){ 
3. try{ 
4. int data=25/0; 
5. System.out.println(data); 
6. } 
7. catch(ArithmeticException e){System.out.println(e);} 
8. finally{System.out.println("finally block is always executed");} 
9. System.out.println("rest of the code..."); 
10. } 
11. }

Output:Exception in thread main java.lang.ArithmeticException:/ by zero
finally block is always executed
rest of the code…

Rule: For each try block there can be zero or more catch blocks, but only one finally block.
Note: The finally block will not be executed if program exits(either by calling System.exit() or by causing a fatal error that causes the process to abort).

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