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This article mainly introduces "case analysis of Java exception handling mechanism". In daily operation, I believe that many people have doubts about the case analysis of Java exception handling mechanism. The editor consulted all kinds of data and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts of "case analysis of Java exception handling mechanism". Next, please follow the editor to study!

The underlying principle of exception handling mechanism

Throw an exception, and if an exception is sent when a method is executed, the method generates an object that represents the exception, stops the currently executing path, and submits the exception to jre.

Catch exception: after jre gets the exception, it falsely invokes the corresponding code to handle the exception. Jre looks in the method's call stack and starts backtracking from the method that generated the exception until the corresponding exception handling code is found.

Inheritance diagram of exception

Oak, we now know what the definition of an exception is, so how should we catch an exception and then handle it.

Exception handling 1. Try-catch-finally structure

First, let's look at a piece of code:

Package AbnormalTest;import java.util.InputMismatchException;import java.util.Scanner;public class test1 {public static void main (String [] args) {Scanner input = new Scanner (System.in); try {System.out.print ("Please enter divisor:"); int a = input.nextInt (); System.out.print ("Please enter divisor:"); int b = input.nextInt () Int sum = bgamma; System.out.println ("result:" + sum); System.out.println ("Program no exception, execution complete!") ;} catch (Exception e) {/ / General exception / / printStackTrace () method is to print out the error message of the stack exception (we usually commit or roll back the transaction after the later learning framework) e.printStackTrace (); System.out.println ("Program exception, please try again!") ; return;} finally {/ / whether an exception occurs or not, the code in the finally is executed, which is usually used to close the System.out.println ("- -") of the resource. System.out.println ("Program is finished, resources have been closed, welcome to use again"); input.close (); / / close the Scanner object to save resources}

Code interpretation:

There are try-catch-finally structures in the above code. What are their respective functions?

Try: we use try to include code that may have exceptions.

Catch: whenever an exception occurs at run time of the code in the try code block, it will enter catch to catch the exception

Finally: no matter how the previous code is executed, the code block of finally will be executed!

Example of run result:

When normal:

In case of exception:

When the divisor is 0, an exception will be triggered and captured in the catah. However, the program output in the finally will be executed regardless of whether there is any exception or not: the program is finished and the resource has been closed. Welcome to use it again.

Second, multiple catch handles different exceptions:

We know that there may be more than one exception in a piece of code, such as the above code, there may be an exception divided by 0, an input exception that may be calculated by entering characters, or a numeric formatting exception, and so on, so that we can use multiple catch to catch exceptions:

Take the above code as an example:

Import java.util.InputMismatchException;import java.util.Scanner;public class test1 {public static void main (String [] args) {Scanner input = new Scanner (System.in); try {System.out.print ("Please enter divisor:"); int a = input.nextInt (); System.out.print ("Please enter divisor:"); int b = input.nextInt () Int sum = bgamma; System.out.println ("result:" + sum); System.out.println ("Program no exception, execution complete!") ;} catch (InputMismatchException e) {/ / multiple catch structure, where an input exception e.printStackTrace (); System.out.println ("program input exception, please try again!") ;} catch (Exception e) {/ / A general exception is caught here (other exceptions can be caught here) e.printStackTrace (); System.out.println ("Program exception, please try again!") ; return;} finally {/ / whether an exception occurs or not, the code in the finally is executed, which is usually used to close the System.out.println ("- -") of the resource. System.out.println ("Program is finished, resources have been closed, welcome to use again"); input.close (); / / close the Scanner object to save resources}

When the input is not a number:

So we can see that it has been captured in the first catch.

3. Throws declares an exception / throw throws an exception:

Suppose I define a method that tells the method that it may send some exception (declare an exception), and the caller must handle the exception when calling the method.

First, let's define an error class:

Student category:

Package ExceptionText;/** * exception testing * / public class Student {private String name; private int age; private char sex; public void setName (String name) {this.name = name;} public String getName () {return name;} public int getAge () {return age;} public char getSex () {return sex } public void setAge (int age) throws Exception {if (age)

0) {this.age = age;} else {throw new Exception ("Age entered incorrectly!") ;} public void setSex (char sex) throws Exception {if (sex = = 'male' | | sex = = 'female') {this.sex = sex;} else {throw new Exception ("incorrect gender input");}

Test class:

Package ExceptionText;public class TestMain {public static void main (String [] args) {Student stu = new Student (); stu.setName ("Xiao Hong"); try {stu.setAge (50); stu.setSex ('k'); System.out.println ("my name is: + stu.getName () +" Age: "+ stu.getAge () +" my gender is: "+ stu.getSex ()) } catch (Exception e) {e.printStackTrace ();}

When both entry and exit are correct:

When the age is entered incorrectly:

When the gender input is incorrect:

Note: if there is more than one exception, the first exception is thrown.

4. Custom exception:

When the subclasses of RuntimeException runtime exceptions can not meet our needs, we can also customize runtime exceptions and throw custom exception information to meet our needs, but we should note that custom runtime exceptions inherit RuntimeException exceptions!

Custom exception class:

/ / this class inherits the RuntimeExceptionpublic class AgeException extends RuntimeException {/ / constructor public AgeException (String message) {super (message);}}

Student information category:

Package CustomizeException;public class Student {private String name; private int age; private char sex; public void setName (String name) {this.name = name;} public String getName () {return name;} public int getAge () {return age;} public char getSex () {return sex } / / method / / use throws to declare an exception, that is, there may be an exception in this method. Declare public void setAge (int age) throws Exception {if (age) beforehand.

0) {this.age = age;} else {/ / if it does not match the above if, judge throw new Exception ("Age entered incorrectly!") ; / / here you will use thrwo to throw an exception.}} public void setSex (char sex) throws Exception {if (sex = = 'male' | | sex = = 'female') {this.sex = sex;} else {throw new AgeException ("this is a custom exception, gender input error");}

Test class:

Package ExceptionText;public class TestMain {public static void main (String [] args) {Student stu = new Student (); stu.setName ("Xiao Hong"); try {stu.setAge (18); stu.setSex ('female'); System.out.println ("my name is: + stu.getName () +" Age: "+ stu.getAge () +" my gender is: "+ stu.getSex ()) } catch (Exception e) {e.printStackTrace ();}

The code in this section is consistent with that in part 3 above, and you can refer to the example above.

5. Common anomalies

At this point, the study on "case analysis of Java exception handling mechanism" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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