Things to Know Part 6

Exception:

                java.lang.Object

                        ↑

                java.lang.Throwable

                ↗                ↖

java.lang.Exception                java.lang.Error

        ↑

java.lang.RuntimeException

        Checked:

                -checked exceptions come from the Exception class and all subclasses that DO NOT extend from the RuntimeException class.

                -programs are required to handle checked exceptions

                FileNotFoundException - thrown programmatically

                        subclass of IOException

IOException - thrown programmatically        

        Unchecked:

                -unchecked exceptions come from the RuntimeException class and all of its subclasses.

                -programs are not required to handle unchecked exceptions

                -can be thrown by programmer or JVM

                ArithmeticException - thrown by JVM

                ArrayIndexOutOfBoundsException - thrown by JVM

                ClassCastException - thrown by JVM

                IllegalArgumentException - thrown by JVM

                NullPointerException - thrown by JVM

                NumberFormatException - thrown by programmer

Errors:

        -extend from Error class

        ExceptionInInitializerError - thrown by JVM

        StackOverflowError - thrown by JVM

        NoClassDefFoundError - thrown by JVM

Try Statements:

        try{ /*must have one or more of the following */}

catch(RuntimeException e) { /* can be any subclass of Exception */}

catch(Exception e) { /* can have multiple catches but only one will run. */

/*Must be higher or equal class level of previous catch. */ }

finally { /*optional. runs after try or catch. */

/* can only have one */ }

Throwing Exceptions:

        -use throw keyword and then but an Exception object.

throw new Exception();

                        or

                Exception e = new Exception();

                throw e;

                        takes optional parameter of string in constructor

                throw new Exception("Main Class, runStuff(int) method");

Methods Declaring Exceptions

        -use throws keyword to indicate that anyone calling this method may potentially need to handle exception.

                public void someMethod() throws IllegalArgumentException {

                        //code for method goes here

                        //method DOES NOT have to throw an IllegalArgumentException

                        //but it would do so like this:

                        throw new IllegalArgumentException();

                }

                //anywhere this method gets called, it must either be surrounded by a try/catch

//block, or the method it gets called from

//must also throw an IllegalArgumentException.

                        EXAMPLE:

                        try {

                                someMethod();

                        }catch(IllegalArgumentException e){

                                //can also take any superclass of IllegalArgumentException

                        }

source:

Boyarsky, Jeanne, and Scott Selikoff. OCA Oracle Certified Associate. Study Guide. John Wiley & Sons, 2015.