Throw keyword in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the throw keyword do in Java?

The throw keyword is used to explicitly throw an exception from a method or block of code. It signals that an error or unusual condition has occurred.

beginner

How is throw different from throws in Java?

throw is used to actually throw an exception object, while throws is used in a method signature to declare that the method might throw certain exceptions.

beginner

Can you throw any object using throw in Java?

No, you can only throw objects that are instances of Throwable or its subclasses, such as Exception or Error.

beginner

What happens after an exception is thrown using throw?

The normal flow of the program stops, and Java looks for a matching catch block to handle the exception. If none is found, the program terminates.

beginner

Show a simple example of using throw to throw an exception.

Example:<br>

if (age < 18) {<br>  throw new IllegalArgumentException("Age must be 18 or older");<br>}

What type of object can be thrown using the throw keyword?

A Only primitive types

B Any object

C Only String objects

D Only objects of type Throwable or its subclasses

Only objects that inherit from Throwable, such as Exception or Error, can be thrown.

Which keyword is used to declare exceptions a method might throw?

A throw

B try

C throws

D catch

throws declares exceptions in method signatures; throw actually throws an exception.

What happens immediately after an exception is thrown with throw?

A The program looks for a matching catch block

B The exception is ignored

C The program continues normally

D The exception is automatically handled

Java searches for a catch block that matches the thrown exception to handle it.

Can you throw multiple exceptions at once using a single throw statement?

A Yes

B No

C Only if they are of the same type

D Only in Java 17+

A single throw statement throws only one exception object.

Which of the following is a correct way to throw an exception?

A throw new Exception("Error occurred");

B throws new Exception("Error occurred");

C throw Exception("Error occurred");

D catch new Exception("Error occurred");

The correct syntax to throw an exception is using throw followed by a new exception object.

Explain how the throw keyword works in Java and when you would use it.

Think about signaling errors manually in your code.

Describe the difference between throw and throws in Java exception handling.

One is for declaring, the other is for actually throwing.