Catch Multiple Exceptions Before & After Java 7 (examples)

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• Java Exceptions & Errors
  • Error vs Exception
  • throw vs throws vs throwable
  • OOM Error
  • Checked vs Unchecked Exception
  • try with resources & AutoCloseable
  • Handle Multiple exceptions
  • Custom unchecked exception
  • User Defined Runtime Exception

What is exception (background)?

• Exception occurs in an application mostly due to programming mistakes.
• e.g. NullPointerException occurs, when we try to access uninitialized objects
• e.g. ArrayIndexOutOfBoundsException occurs, when we try to access the array index beyond its bounds.
• We catch the exceptions using catch blocks and recover from them.
  • e.g. If ArrayIndexOutOfBoundsException occurs, in catch block we can introspect the error condition, correct the exception condition and resume the normal flow of application.
• If we are expecting multiple exceptions, we can catch exceptions using catch blocks.
• We will catch multiple exceptions with & without using java 7 feature.
  • Java 7 has introduced the multi catch block feature.
• Catch multiple exceptions without using Java 7 feature (prior to java 7)

Catch multiple exceptions in java (prior to java7)

try { /* Code can throw NullPointerException or IOException exception, we are catching individual exceptions. */ } catch (FileNotFoundException e) { System.out.println("1.1. Exception FileNotFoundException, message: " + e.getMessage()); } catch (IOException e) { System.out.println("1.2. Exception IOException, message: " + e.getMessage()); }

Catch multiple exceptions in single catch block using Java 7

• We will catch multiple exceptions using single catch block.
• Each exceptions should be separated by pipe or vertical bar (|).
• If catch block handling more than one exception then exception parameter implicitly becomes final parameter.
• The exception types in multiple catch block must be disjoint, one exception cannot be a subclass of another exception.

try { /* Code can throw NullPointerException or IOException exception, catching exceptions in single block.*/ } /* Catching multiple exceptions in same block. */ catch (NullPointerException | IOException e) { System.out.println("3.3. Exception NullPointerException, message: " + e.getMessage()); }

Program – catch multiple exceptions before & after java 7

package org.learn.client; import java.io.BufferedReader; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.IOException; public class CatchMultiExceptionsDemo { public static void main(String[] args) { System.out.println("1. Catching multiple exception prior to java 7:"); catchMultipleExceptionsPriorJava7(); System.out.println("\n2. Catching multiple exception after java 7:"); catchMultipleExceptionsAfterJava7(); } private static void catchMultipleExceptionsPriorJava7() { BufferedReader in = null; try { in = new BufferedReader(new FileReader("NonExistedFilePath.txt")); in.read(); } catch (FileNotFoundException e) { System.out.println("1.1. FileNotFoundException,message: " + e.getMessage()); } catch (IOException e) { System.out.println("1.2. IOException, message: " + e.getMessage()); } finally { try { in.close(); } catch (NullPointerException e) { System.out.println("1.3 NullPointerException,message: " + e.getMessage()); } catch (IOException e) { System.out.println("1.4. IOException,message: " + e.getMessage()); } } } private static void catchMultipleExceptionsAfterJava7() { BufferedReader in = null; try { in = new BufferedReader(new FileReader("NonExistedFilePath.txt")); in.read(); } /* * Exceptions should be disjoint, FileNotFoundException is sub class of * IOException so, we can not catch FileNotFountException & IOException * in same catch block. */ catch (FileNotFoundException e) { System.out.println("2.1 FileNotFoundException,message: " + e.getMessage()); } catch (IOException e) { System.out.println("2.2 IOException,message: " + e.getMessage()); } finally { try { in.close(); } /* Catching multiple exceptions in same block. */ catch (NullPointerException | IOException e) { System.out.println("2.3 Exception occurred,message: " + e.getMessage()); } } } }

Output – catch multiple exceptions before & after java 7

1. Catching multiple exception prior to java 7: 1.1. FileNotFoundException,message: NonExistedFilePath.txt (The system cannot find the file specified) 1.3 NullPointerException,message: null 2. Catching multiple exception after java 7: 2.1 FileNotFoundException,message: NonExistedFilePath.txt (The system cannot find the file specified) 2.3 Exception occurred,message: null

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