how throw exception java code example

Example 1: throw io exception java

public static void foo() throws IOException {
    // some code here, when something goes wrong, you might do:
    throw new IOException("error message");
}

public static void main(String[] args) {
    try {
        foo();
    } catch (IOException e) {
        System.out.println(e.getMessage());
    }
}

Example 2: java how to throw exception

public class ThrowException{
  public static void main(String [] args) throws Exception{ 
    //throws Exception line is needed if not using try-catch block
    throw new Exception("Errmessage");
  }
}

Example 3: java throw an exception

public static void main(String[] args) {
	Scanner kb = new Scanner(System.in);
    System.out.println("Enter a number");
    try {
    	double nb1 = kb.nextDouble();
    	if(nb1<0)
        	throw new ArithmeticException();
        else System.out.println( "result : " + Math.sqrt(nb1) );
    } catch (ArithmeticException e) {
        System.out.println("You tried an impossible sqrt");
    }
}

Example 4: throw keyword in java

Generally JVM throws the exception and we handle the exceptions by 
using try catch block. But there are situations where we have to throw 
userdefined exceptions or runtime exceptions. In such case we use throw keyword 
to throw exception explicitly.

  Syntax : throw throwableInstance;

Throwable instance must be of type throwable or any of its subclasses.
After the throw statement execution stops and subsequent statements are not 
executed. Once exception object is thrown JVM checks is there any catch 
block to handle the exception. If not then the next catch statement till it 
finds the appropriate handler. If appropriate handler is not found, 
then default exception handler halts the program and prints the description 
and location of exception. In general we use throw keyword for throwing 
userdefined or customized exception.