Notes

• Notes
  • Exceptions
    • Checked Exception
      • LBYL and EAFP
    • Unchecked Exception
    • finally
    • Try-with-resources

Exceptions

---
title: Java Exceptions Hirarchy
---
graph TD
    0(Object)
    1(Throwable)
    2(Error)
    3(OutOfMerory)
    4(StachOverflowError)
    5(LinkageError)
    6(Exception)
    7(IOException)
    8(SocketException)
    9(FileNoteFoundException)
    10(RuntimeException)
    11(IllegalArgumentException)
    12(NumberFormatException)
    13(IndexOutOfBoundsException)
    14(ArrayIndexOutOfBoundsException)
    15(ArithmeticException)
    
    0 --- 1
    1 --- 6
    1 --- 2
    2 --- 3
    2 --- 4
    2 --- 5
    6 --- 7
    7 --- 8
    7 --- 9
    6 --- 10
    10 --- 11
    11 --- 12
    10 --- 13
    13 --- 14
    10 --- 15
    
    classDef Red fill:#FF0000;
    classDef Amber	fill:#FFA500;
    classDef Green fill:#008000;
    classDef Blue fill:#0000FF;

    class 1 Blue;
    class 2,3,4,5 Red;
    class 10,11,12,13,14,15 Green;
    class 6,7,8,9 Amber;

    linkStyle default fill: none, stroke: grey;

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• The Error class indicates serious problems, that a reasonable application shouldn't try to catch or recover from
• There are two types of Exceptions, those that subclass from RuntimeException, and those that don't

Checked Exception

A checked exception represents an anticipated or common problem, that might occur

We have two ways to handle checked exceptions:

• We can wrap the statement that throws a checked exception, in a try catch block, and then handle the situation in the catch block
• We can change the method signature, declaring a throws clause, and specifying this exception type

LBYL and EAFP

• "Look Before You Leap" or LBYL - style of coding involves checking for errors, before you perform an operation
• EAFP stands for, "Easier to Ask Forgiveness than Permission" assumes an operation will usually succeed, and then handles any errors that occur, if they do occur

Feature	LBYL	EAFP
Approach	Check for errors before performing an operation	Assume that the operation will succeed and handle any errors that occur
Advantages	Can be more efficient if errors are rare	Can be more concise and easier to read
Disadvantages	Can be more verbose if errors are common	Can be more difficult to debug if errors are unexpected

Unchecked Exception

• A checked exception means it's NOT an unchecked exception :)
• An Unchecked Exception is an instance of a RuntimeException, or one if its subclasses

finally

The original purpose for the finally clause, was to have a single block of code to perform cleanup operations

• Is used in conjunction with a try statement
• A traditional try statement requires either a catch or a finally clause, or can include both
• It is always declared after the catch block if one is declared
• Its code is always executed, regardless of what happens in the try or catch blocks
• Does not have access to either the try or catch block's local variables

Disadvantages:

• It can be difficult to read and understand code, that uses this clause
• It can be used to hide errors, which can make debugging more difficult
• If We execute code that's not related to clean up tasks, this will make it harder to maintain our code

Try-with-resources

try-with-resources examples	traditional try clause

• The try-with-resources takes a colon delimited list of resource variables
• The resources in this list must implement the AutoCloseable or the Closeable interface
• The try-with-resources statement can be used without a fnally block, because all resources are automatically closed when this type of try block completes, or if it gets an exception