3- Types of Exceptions

Jun 18, 2026 03:34 · 3:40 · English · Whisper Turbo · 2 speakers

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Lecture Index

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In Java,

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we have three types of exceptions.

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Checked exceptions,

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unchecked exceptions,

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also called runtime exceptions,

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and errors.

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A lot of people new to Java find this confusing,

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so let me make it super simple for you.

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Checked exceptions are exceptions that we developer should anticipate and

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handle properly.

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For example,

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let's say we want to read data from a file.

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What if the file doesn't exist?

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Maybe it got deleted just before we tried to open it for reading.

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Good developers always anticipate and handle these edge cases.

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So instead of letting the runtime terminate our program,

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we would better display a friendly message to the user saying,

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hey,

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that file doesn't exist.

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Now,

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the good news is that the Java compiler enforces us to handle these errors.

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That is why they're called checked exceptions because they get checked at compile

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time. Let me show you.

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Let's create a new file reader for reading data from a file so reader

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equals new file reader Let's say

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file that txt now look at this read underline the Java

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compiler knows that the constructor of the file reader will throw an exception

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if the file doesn't exist So it's telling us hey you haven't handled

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this exception file not found exception.

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This is an example of a checked exception

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So checked exceptions are exceptions that we should anticipate and recover from

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and that is why they're called checked exceptions because the Java compiler checks

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them at compile time.

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Now the second type of exception is called unchecked exception or runtime

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exception.

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As the name implies,

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these exceptions are not checked by the compiler at compile time.

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They occur because of programming errors.

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Null pointer exception is an example of a runtime exception.

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In the last video,

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we shouldn't have passed null to the say hello method.

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This is a programming error.

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So unlike checked exceptions,

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we don't want to anticipate and recover by displaying a friendly message

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like, hey,

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we made a mistake and try to use an object reference with the null value.

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Doesn't make sense.

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Instead, we should prevent exceptions like this from happening in the first place.

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How can we do that?

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By good coding practices and testing,

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a lot of testing,

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preferably automated testing.

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That's a topic for an entirely different course.

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Now,

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other examples of runtime exceptions are arithmetic exception.

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This gets thrown if you try to divide a value by zero.

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You also have illegal argument exception for indicating that

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the argument we passed to a method was not accepted.

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Again, this is a programming mistake,

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not a kind of error that we should anticipate and validate.

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Another runtime exception you may see is the index out of bounds exception,

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which occurs if we try to access an element in an array or a string

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or a list using an invalid index.

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For example,

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we have five elements in an array,

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but we try to access the 10th element.

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Another popular runtime exception is illegal set exception,

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which gets thrown if we try to call a method,

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but the underlying object is not in the right state.

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So these are runtime exceptions.

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The third type of exception we have in Java is an error which indicates

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an error external to our application.

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Examples are stack overflow error or out of memory error.

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So if the Java virtual machine runs out of memory,

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there's nothing we can do about it.

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So just like runtime exceptions,

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we should let the application crash rather than display a friendly message to

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the user.

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We should try to identify the source of these errors.

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These errors can happen because of programming errors like an infinite recursion

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or for reasons outside of our application like a problem in the Java virtual

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machine itself.

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Next,

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we're going to look at the hierarchy of exception classes in Java.

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