Java try-catch block

Java try block

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

snippet
try{  
//code that may throw an exception  
}catch(Exception_class_Name ref){}

Syntax of try-finally block

snippet
try{  
//code that may throw an exception  
}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

snippet
public class TryCatchExample1 {

	public static void main(String[] args) {
		
		int data=50/0; //may throw exception 
		
		System.out.println("rest of the code");
		
	}
	
}

Output:

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

snippet
public class TryCatchExample2 {

	public static void main(String[] args) {
		try
		{
		int data=50/0; //may throw exception 
		}
            //handling the exception
		catch(ArithmeticException e)
		{
			System.out.println(e);
		}
		System.out.println("rest of the code");
	}
	
}

Output:

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.

snippet
public class TryCatchExample3 {

	public static void main(String[] args) {
		try
		{
		int data=50/0; //may throw exception 
                         // if exception occurs, the remaining statement will not exceute
		System.out.println("rest of the code");
		}
             // handling the exception 
		catch(ArithmeticException e)
		{
			System.out.println(e);
		}
		
	}
	
}

Output:

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.

snippet
public class TryCatchExample4 {

	public static void main(String[] args) {
		try
		{
		int data=50/0; //may throw exception 
		}
            // handling the exception by using Exception class    
		catch(Exception e)
		{
			System.out.println(e);
		}
		System.out.println("rest of the code");
	}
	
}

Output:

Output
java.lang.ArithmeticException: / by zero rest of the code

Example 5

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

snippet
public class TryCatchExample5 {

	public static void main(String[] args) {
		try
		{
		int data=50/0; //may throw exception 
		}
             // handling the exception
		catch(Exception e)
		{
                  // displaying the custom message
			System.out.println("Can't divided by zero");
		}
	}
	
}

Output:

Output
Can't divided by zero

Example 6

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

snippet
public class TryCatchExample6 {

	public static void main(String[] args) {
		int i=50;
		int j=0;
		int data;
		try
		{
		data=i/j; //may throw exception 
		}
            // handling the exception
		catch(Exception e)
		{
             // resolving the exception in catch block
			System.out.println(i/(j+2));
		}
	}
}

Output:

Output
25

Example 7

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

snippet
public class TryCatchExample7 {

	public static void main(String[] args) {
		
		try
		{
		int data1=50/0; //may throw exception 

		}
             // handling the exception
		catch(Exception e)
		{
            // generating the exception in catch block
		int data2=50/0; //may throw exception 

		}
	System.out.println("rest of the code");
	}
}

Output:

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).

snippet
public class TryCatchExample8 {

	public static void main(String[] args) {
		try
		{
		int data=50/0; //may throw exception 

		}
            // try to handle the ArithmeticException using ArrayIndexOutOfBoundsException
		catch(ArrayIndexOutOfBoundsException e)
		{
			System.out.println(e);
		}
		System.out.println("rest of the code");
	}
	
}

Output:

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

Example 9

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

snippet
public class TryCatchExample9 {

	public static void main(String[] args) {
		try
		{
		int arr[]= {1,3,5,7};
		System.out.println(arr[10]); //may throw exception 
		}
            // handling the array exception
		catch(ArrayIndexOutOfBoundsException e)
		{
			System.out.println(e);
		}
		System.out.println("rest of the code");
	}
	
}

Output:

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

Example 10

Let's see an example to handle checked exception.

snippet
import java.io.FileNotFoundException;
import java.io.PrintWriter;

public class TryCatchExample10 {

	public static void main(String[] args) {
		
		
		PrintWriter pw;
		try {
			pw = new PrintWriter("jtp.txt"); //may throw exception 
			pw.println("saved");
		}
// providing the checked exception handler
 catch (FileNotFoundException e) {
			
			System.out.println(e);
		}		
	System.out.println("File saved successfully");
	}
}

Output:

Output
File saved successfully

Internal working of java try-catch block

internal working of try-catch block

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.

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