Java program to demonstrate the use of try and catch blocks

NullPointerException

Codeaft.java

class Codeaft
{
    public static void main(String args[])
    {
        String s=null;
        System.out.println("Length: "+s.length());
    }
}

Output

codeaft@codeaft:~$ javac Codeaft.java
codeaft@codeaft:~$ java Codeaft
Exception in thread "main" java.lang.NullPointerException
    at Codeaft.main(Codeaft.java:6)
codeaft@codeaft:~$

Java program to demonstrate the use of try and catch blocks

Codeaft.java

class Codeaft
{
    public static void main(String args[])
    {
        String s=null;
        try
        {
            System.out.println("Length: "+s.length());
        }
        catch(Exception e)
        {
            System.out.println("String is null, hence, Unable to find the length.");
        }
    }
}

Output

codeaft@codeaft:~$ javac Codeaft.java
codeaft@codeaft:~$ java Codeaft
String is null, hence, Unable to find the length.
codeaft@codeaft:~$

Java program to demonstrate the use of try with multiple catch blocks

Codeaft.java

class Codeaft
{
    public static void main(String args[])
    {
        String s=null;
        try
        {
            System.out.println("Length: "+s.length());
        }
        catch(ArithmeticException e)
        {
            System.out.println("Exception caught in the first catch block");
        }
        catch(NullPointerException e)
        {
            System.out.println("Exception caught in the second catch block");
        }
        catch(Exception e)
        {
            System.out.println("Exception caught in the third catch block");
        }
    }
}

Output

codeaft@codeaft:~$ javac Codeaft.java
codeaft@codeaft:~$ java Codeaft
Exception caught in the second catch block
codeaft@codeaft:~$

Java program to handle the NullPointerException using Exception class

Codeaft.java

class Codeaft
{
    public static void main(String args[])
    {
        String s=null;
        try
        {
            System.out.println("Length: "+s.length());
        }
        catch(ArithmeticException e)
        {
            System.out.println("Exception caught in the first catch block");
        }
        catch(StringIndexOutOfBoundsException e)
        {
            System.out.println("Exception caught in the second catch block");
        }
        catch(Exception e)
        {
            System.out.println("Exception caught in the third catch block");
        }
    }
}

Output

codeaft@codeaft:~$ javac Codeaft.java
codeaft@codeaft:~$ java Codeaft
Exception caught in the third catch block
codeaft@codeaft:~$

Java program to handle the NullPointerException using RuntimeException class

Codeaft.java

class Codeaft
{
    public static void main(String args[])
    {
        String s=null;
        try
        {
            System.out.println("Length: "+s.length());
        }
        catch(ArithmeticException e)
        {
            System.out.println("Exception caught in the first catch block");
        }
        catch(RuntimeException e)
        {
            System.out.println("Exception caught in the second catch block");
        }
        catch(Exception e)
        {
            System.out.println("Exception caught in the third catch block");
        }
    }
}

Output

codeaft@codeaft:~$ javac Codeaft.java
codeaft@codeaft:~$ java Codeaft
Exception caught in the second catch block
codeaft@codeaft:~$

The following sequence of multiple catch blocks are not allowed

Codeaft.java

class Codeaft
{
    public static void main(String args[])
    {
        String s=null;
        try
        {
            System.out.println("Length: "+s.length());
        }
        catch(Exception e)
        {
            System.out.println("Exception caught in the third catch block");
        }
        catch(RuntimeException e)
        {
            System.out.println("Exception caught in the second catch block");
        }
        catch(ArithmeticException e)
        {
            System.out.println("Exception caught in the first catch block");
        }
    }
}

Output

codeaft@codeaft:~$ javac Codeaft.java
codeaft@codeaft:~$ java Codeaft
Codeaft.java:14: error: exception RuntimeException has already been caught
        catch(RuntimeException e)
        ^
Codeaft.java:18: error: exception ArithmeticException has already been caught
        catch(ArithmeticException e)
        ^
2 errors
codeaft@codeaft:~$

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