JAVA EE: Java Tutorial : Java Exception handling (Unreachable catch block)

Tuesday, 21 June 2016

Java Tutorial : Java Exception handling (Unreachable catch block)

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Java Tutorial : Java Exception handling (Unreachable catch block)

ExceptionDemo1.java

public class ExceptionDemo1
{
    public static void main(String[] args)
    {

        String firstName = null;

        try
        {
            // It will throw NullPointerException
            System.out.println(firstName.length());
        }
        catch (NullPointerException nullPointerException)
        {
            System.out.println("String value is null.");
        }
        catch (Exception exception)
        {
            exception.printStackTrace();
        }

        String lastName = "Peter";
        String fullName = firstName + lastName;
        System.out.println("fullName = " + fullName);

    }

}

Output

String value is null.
fullName = nullPeter

ExceptionDemo2.java

public class ExceptionDemo2
{
    public static void main(String[] args)
    {
        String firstName = null;

        try
        {
            // It will throw NullPointerException
            System.out.println(firstName.length());
        }
        catch (Exception exception)
        {
            exception.printStackTrace();
        }

        String lastName = "Peter";
        String fullName = firstName + lastName;
        System.out.println("fullName = " + fullName);
    }
}

Output

java.lang.NullPointerException
    at ExceptionDemo2.main(ExceptionDemo2.java:10)
fullName = nullPeter

ExceptionDemo3.java

public class ExceptionDemo3
{
    public static void main(String[] args)
    {

        String firstName = null;

        try
        {
            // It will throw NullPointerException
            System.out.println(firstName.length());
        }

        catch (Exception exception)
        {
            exception.printStackTrace();
        }

        catch (NullPointerException nullPointerException)
        {
            System.out.println("String value is null.");
        }

        String lastName = "Peter";
        String fullName = firstName + lastName;
        System.out.println("fullName = " + fullName);

    }
}

Output

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
    Unreachable catch block for NullPointerException. It is already handled by the catch block for Exception

    at ExceptionDemo3.main(ExceptionDemo3.java:19)