Throws in exception handling in java
Throws keyword in java is used to declare exceptions that can be thrown by the method. Throws keyword can be used to throw multiple exception.
syntax:
1. Throws single exception
1 | methodName(methodParams ..) throws exceptionNames |
example:
1 | public readFile(String fileName) throws IOException |
2. Throws multiple exception
1 | methodName(methodParams ..) throws exceptionName1,exceptionName2,... |
example:
1 | public readFile(String fileName) throws IOException,FileNotFoundException |
When a method throws an exception, the code that uses this method needs to handle this exception.
Handling of exception can be of 2 types
1. Use a Try-Catch block
2. Use throws method to again throw the same or new exception.
Lets see an example where we have a method convertListToString that throws exception.
In main method we call the convertListToString and also handle the exception that was thrown.
Example : Throws in exception handling
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 | package com.kscodes.sampleproject; import java.io.IOException; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class ExecptionHandling { public static void main(String[] args) { List<String> arrList1 = new ArrayList<>(Arrays.asList("Java", "JSP", "JavaScript", "JQuery")); try { System.out.println("Converting ArrayList 1"); String convertedList = convertListToString(arrList1); System.out.println(convertedList); } catch (IOException e) { System.out .println("Exception while converting ArrayList 1. Exception Message is " + e.getMessage()); } System.out.println("**********************************************"); List<String> arrList2 = null; try { System.out.println("Converting ArrayList 2 which was null"); String convertedList = convertListToString(arrList2); System.out.println(convertedList); } catch (IOException e) { System.out.println("Exception while converting ArrayList 2."); e.printStackTrace(); } } public static String convertListToString(List<String> list) throws IOException { /* * Check if list is null and then throw IOException */ if (list == null) { throw new IOException(); } String convertedString = ""; for (String str : list) { convertedString = convertedString + str; } return convertedString; } } |
Output
1 2 3 4 5 6 7 8 | Converting ArrayList 1 JavaJSPJavaScriptJQuery ********************************************** Converting ArrayList 2 which was null Exception while converting ArrayList 2. java.io.IOException at com.kscodes.sampleproject.ExecptionHandling.convertListToString(ExecptionHandling.java:44) at com.kscodes.sampleproject.ExecptionHandling.main(ExecptionHandling.java:29) |
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