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As seen in the previous post, we need to construct an instance of a user-defined exception; the Java runtime cannot detect and create instances of user-defined exceptions.
Sometimes we may find that the exception messages given by the standard exception classes are not intuitive, and it may be necessary to provide more elaborate messages to the application user.
The throw keyword (note the singular form) is used to force an exception.
Let’s recall the rules we learn from previous post about declaring exception in Overriding Methods.
A class definition serves as a template from which we create objects for the use of our application code
A constructor is a special method that the runtime executes during the object-creation process. In previous parts, we saw that the following statement calls the class constructor:
At the top of the Exception class hierarchy we have the Throwable class. All other exception classes, including our own designed exception classes, inherit from the Throwable class.
We may have a finally block in conjunction with a try block without a catch block. In other words
Let’s now look at an example where the running code generates multiple types of exceptions.
If an inner class is declared with a public access modifier, it can be instantiated from outside the scope of its enclosing class.
To create a static nested class, we use the static keyword in front of the class declaration, the same way we declare a static field or a method within the enclosing class.
In the previous post, we created a standard interface to get the fuel efficiency of a car. A car has many such standard functions that could be defined in terms of interfaces.