In this tutorial, we will learn to use throw and throws keyword for exception handling with the help of examples.<\/p>\n\n\n\n
In Java, exceptions can be categorized into two types:<\/p>\n\n\n\n
ArithmeticException<\/code>, NullPointerException<\/code>, ArrayIndexOutOfBoundsException<\/code>, exceptions under Error<\/code> class, etc.<\/li>- Checked Exceptions:<\/strong> They are checked at compile-time. For example,
IOException<\/code>, InterruptedException<\/code>, etc.<\/li><\/ul>\n\n\n\nRefer to\u00a0Java Exceptions\u00a0to learn in detail about checked and unchecked exceptions.<\/p>\n\n\n\n
Usually, we don’t need to handle unchecked exceptions. It’s because unchecked exceptions occur due to programming errors. And, it is a good practice to correct them instead of handling them.<\/p>\n\n\n\n
This tutorial will now focus on how to handle checked exceptions using throw<\/code> and throws<\/code>.<\/p>\n\n\n\n
\n\n\n\nJava throws keyword<\/h2>\n\n\n\n
We use the throws<\/code> keyword in the method declaration to declare the type of exceptions that might occur within it.<\/p>\n\n\n\nIts syntax is:<\/p>\n\n\n\n
accessModifier returnType methodName() throws ExceptionType1, ExceptionType2 \u2026 {\n \/\/ code\n}\n<\/code><\/pre>\n\n\n\nAs you can see from the above syntax, we can use throws<\/code> to declare multiple exceptions.<\/p>\n\n\n\n
\n\n\n\nExample 1: Java throws Keyword<\/h3>\n\n\n\nimport java.io.*;\nclass Main {\n public static void findFile() throws IOException {\n \/\/ code that may produce IOException\n File newFile=new File(\"test.txt\");\n FileInputStream stream=new FileInputStream(newFile);\n }\n\n public static void main(String[] args) {\n try{\n findFile();\n } catch(IOException e){\n System.out.println(e);\n }\n }\n}\n<\/code><\/pre>\n\n\n\nOutput<\/strong><\/p>\n\n\n\njava.io.FileNotFoundException: test.txt (No such file or directory)\n<\/samp><\/code><\/pre>\n\n\n\nWhen we run this program, if the file test.txt<\/code> does not exist, FileInputStream<\/code> throws a FileNotFoundException<\/code> which extends the IOException<\/code> class.<\/p>\n\n\n\nIf a method does not handle exceptions, the type of exceptions that may occur within it must be specified in the throws<\/code> clause so that methods further up in the call stack can handle them or specify them using throws<\/code> keyword themselves.<\/p>\n\n\n\nThe findFile()<\/code> method specifies that an IOException<\/code> can be thrown. The main()<\/code> method calls this method and handles the exception if it is thrown.<\/p>\n\n\n\n
\n\n\n\nThrowing multiple exceptions<\/h3>\n\n\n\n
Here’s how we can throw multiple exceptions using the throws<\/code> keyword.<\/p>\n\n\n\nimport java.io.*;\nclass Main {\n public static void findFile() throws NullPointerException, IOException, InvalidClassException {\n \n \/\/ code that may produce NullPointerException\n \u2026 \u2026 \u2026 \n\n \/\/ code that may produce IOException\n \u2026 \u2026 \u2026 \n\n \/\/ code that may produce InvalidClassException \n \u2026 \u2026 \u2026 \n }\n\n public static void main(String[] args) {\n try{\n findFile();\n } catch(IOException e1){\n System.out.println(e1.getMessage());\n } catch(InvalidClassException e2){\n System.out.println(e2.getMessage());\n }\n }\n}\n<\/code><\/pre>\n\n\n\nHere, the findFile()<\/code> method specifies that it can throw NullPointerException<\/code>, IOException<\/code>, and InvalidClassException<\/code> in its throws<\/code> clause.<\/p>\n\n\n\nNote that we have not handled the NullPointerException<\/code>. This is because it is an unchecked exception. It is not necessary to specify it in the throws<\/code> clause and handle it.<\/p>\n\n\n\n
\n\n\n\nthrows keyword Vs. try…catch…finally<\/h3>\n\n\n\n
There might be several methods that can cause exceptions. Writing try...catch<\/code> for each method will be tedious and code becomes long and less-readable.<\/p>\n\n\n\nthrows<\/code> is also useful when you have checked exception (an exception that must be handled) that you don’t want to catch in your current method.<\/p>\n\n\n\n
\n\n\n\nJava throw keyword<\/h2>\n\n\n\n
The throw<\/code> keyword is used to explicitly throw a single exception.<\/p>\n\n\n\nWhen an exception is thrown, the flow of program execution transfers from the try<\/code> block to the catch<\/code> block. We use the throw<\/code> keyword within a method.<\/p>\n\n\n\nIts syntax is:<\/p>\n\n\n\n
throw throwableObject;<\/code><\/pre>\n\n\n\nA throwable object is an instance of class Throwable<\/code> or subclass of the Throwable<\/code> class.<\/p>\n\n\n\n
\n\n\n\nExample 2: Java throw keyword<\/h3>\n\n\n\nclass Main {\n public static void divideByZero() {\n throw new ArithmeticException(\"Trying to divide by 0\");\n }\n\n public static void main(String[] args) {\n divideByZero();\n }\n}\n\n<\/code><\/pre>\n\n\n\nOutput<\/strong><\/p>\n\n\n\nException in thread \"main\" java.lang.ArithmeticException: Trying to divide by 0\n at Main.divideByZero(Main.java:3)\n at Main.main(Main.java:7)\nexit status 1\n<\/samp><\/code><\/pre>\n\n\n\nIn this example, we are explicitly throwing an ArithmeticException.<\/code><\/p>\n\n\n\nNote:<\/strong> ArithmeticException<\/code> is an unchecked exception. It’s usually not necessary to handle unchecked exceptions.<\/p>\n\n\n\n
\n\n\n\nExample 3: Throwing checked exception<\/h3>\n\n\n\nimport java.io.*;\nclass Main {\n public static void findFile() throws IOException {\n throw new IOException(\"File not found\");\n }\n\n public static void main(String[] args) {\n try {\n findFile();\n System.out.println(\"Rest of code in try block\");\n } catch (IOException e) {\n System.out.println(e.getMessage());\n }\n }\n}\n<\/code><\/pre>\n\n\n\nOutput<\/strong><\/p>\n\n\n\nFile not found\n<\/samp><\/code><\/pre>\n\n\n\nThe findFile()<\/code> method throws an IOException<\/code> with the message we passed to its constructor.<\/p>\n\n\n\nNote that since it is a checked exception, we must specify it in the throws<\/code> clause.<\/p>\n\n\n\nThe methods that call this findFile()<\/code> method need to either handle this exception or specify it using throws<\/code> keyword themselves.<\/p>\n\n\n\nWe have handled this exception in the main<\/code>()<\/code> method. The flow of program execution transfers from the try<\/code> block to catch<\/code> block when an exception is thrown. So, the rest of the code in the try<\/code> block is skipped and statements in the catch<\/code> block are executed.<\/p>\n","protected":false},"excerpt":{"rendered":"In this tutorial, we will learn to use throw and throws keyword for exception handling with the help of examples. In Java, exceptions can be categorized into two types: Unchecked Exceptions: They are not checked at compile-time but at run-time.For example: ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException, exceptions under Error class, etc. Checked Exceptions: They are checked at compile-time. For example, IOException, InterruptedException, etc. Refer to\u00a0Java Exceptions\u00a0to […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[569],"tags":[],"_links":{"self":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/1247"}],"collection":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/comments?post=1247"}],"version-history":[{"count":0,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/1247\/revisions"}],"wp:attachment":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/media?parent=1247"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/categories?post=1247"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/tags?post=1247"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}