throw is a keyword in java which is used to throw an exception manually. Using throw keyword, you can throw an exception from any method or block. But, that exception must be of type java.lang.Throwable class or it’s sub classes. throws is also a keyword in java which is used in the method signature to indicate that this method may throw mentioned exceptions. The caller to such methods must handle the mentioned exceptions either using try-catch blocks or using throws keyword. Throwable is a super class for all types of errors and exceptions in java. This class is a member of java.lang package. Only instances of this class or it’s sub classes are thrown by the java virtual machine or by the throw statement. The only argument of catch block must be of this type or it’s sub classes. If you want to create your own customized exceptions, then your class must extend this class. Click here to see the hierarchy of exception classes in java.