try-catch-finally exception handling How to use java

Environment: Windows10, Eclipse, java8

Describes exception handling using try catch finally in java.

How to write exception handling

try{
processing
}catch(Exception type Argument){
Processing when an exception occurs
}finally{
Last action to be executed(With or without exception)
}

Example of use

	public static void main(String[] args) {
		double a = 99999;

		//----------Cases where exception handling occurs----------
		System.out.println("-----Exception occurred-----");
		try {
			a = 30/0;
		}catch(ArithmeticException e) {
			System.out.println("Exception handling: 0 does not break");
			System.out.println(e);
		}finally {
			System.out.println("finally  "+ "a="+a);
		}

		//----------Case where exception handling does not occur----------
		System.out.println("-----normal-----");
		try {
			a = 30/3;
		}catch(ArithmeticException e) {
			System.out.println("Exception handling: 0 does not break");
			System.out.println(e);
		}finally {
			System.out.println("finally  "+ "a="+a);
		}
	}

Execution result

-----Exception occurred-----
Exception handling: 0 does not break
java.lang.ArithmeticException: / by zero
finally  a=99999.0
-----normal-----
finally  a=10.0

Commentary

In the above program, on the line a = 30/0; An exception (ArithmeticException) has occurred because we are dividing by zero (there is no solution). Therefore, the following processing is executed.

		}catch(ArithmeticException e) {
			System.out.println("Exception handling: 0 does not break");
		}

Therefore, as the execution result, "Exception handling: 0 does not break" is displayed.

About catch (exception type argument)

How should I write the contents of catch?

Example above

}catch(ArithmeticException e){

In the above example, ArithmeticException is an exception that is thrown when divided by zero.

Other exceptions can be written in the following form, so I will explain them.

}catch(Exception type Argument){

Exception type (eg ArithmeticException)

Write the type that will be thrown when an exception occurs.

Check the exception handling corresponding to the processing written in try in the reference and use it. For java11: https://docs.oracle.com/javase/jp/11/docs/api/index-files/index-1.html

With import

Also, if you want to handle exceptions in file I / O operations, etc. When using an exception called IOException

import java.io.IOException;

You may also need to import the package with.

Regarding the exception called ArithmeticException this time,

import java.lang.ArithmeticException

It seems that it is necessary to write and import. However, java.lang is implicitly imported within the compiler and does not need to be written. By the way, this is why System.out.println can be used without import.

Argument (example: e)

You can name it freely. "E" is often used.

In this example Because it describes "System.out.println (e);" "Java.lang.ArithmeticException: / by zero" in the execution result Is displayed, and it can be confirmed that an exception has been received.