Please pay attention: caller throws parentexception only!!
Say that aexception, and bexception inherit from parentexception.
In method af, it throws aexception, bexception and parentexception.
void af() throws aexception, bexception, parentexception {}
The method caller calls af and throw parentexception only.
void caller() throws parentexception
Here we lost the information of subclasses of parentexception.
The method rootCaller calls the method caller and rootcaller can only catch parentexception thrown by caller and using the following exception process catch block:
void rootCaller() {
try {
caller();
} catch(parentexception e) {
if(e instanceof aexception) {
......
} else if(e instanceof bexception) {
......
} else if(e instanceof parentexception) {
......
} else {
......
}
}
This is so ugly and very easy to forget some subclass of parentexception if the subclasses are too many.
Is there anyway to improve such code?
Current answer can not give me any idea:
1, rootCaller cannnot use multi-catch to simplify the process cause caller only throw parentexception.
2, because caller only throw parentexception, there is not any other exception check if the af is changed latter to throws more than aexception and bexception, say cexception.
As others have suggested in the comments, you should be using multiple catch clauses.
void rootCaller() {
try {
caller();
} catch (AException e) {
// ...
} catch (ParentException e) {
// ...
} catch (BException e) {
// ...
} catch (AnotherException e) {
// ...
} catch (Exception e) {
// ...
}
}
The order of the catches matters too. The Exception will be tested against each case in turn and only trigger the first one that matches.
So for example with AException and BException extending ParentException in my above code the catch (BException e) block can never be reached as catch (ParentException e) is reached and executed first.
Related
Everytime I run this code, everything works fine, but if deposit methods throws an error,
only the catch in the main method catches the exception and prints the string, despite the catch in the ExceptionsDemo. Why does that happen?
public class ExceptionsDemo {
public static void show() throws IOException {
var account = new Account();
try {
account.deposit(0);//this method might throw an IOException
account.withDraw(2);
} catch (InsufficientFundsException e) {
System.out.println(e.getMessage());
}
}
}
public class Main {
public static void main(String[] args) {
try {
ExceptionsDemo.show();
} catch (IOException e) {
System.out.println("An unexpected error occurred");
}
}
}
This happens because in your show() method, you are catching a specific type of exception called InsufficientFundsException. But the exception thrown by account.deposit() is IOException which is caught only in your main method. That is why the catch in the main method gets executed and not the catch in ExcpetionsDemo
If you want to catch IOException in your ExceptionsDemo class you can do this:
public static void show() {
var account = new Account();
try {
account.deposit(0);//this method might throw an IOException
account.withDraw(2);
} catch (InsufficientFundsException e) {
System.out.println(e.getMessage());
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
A single try block can have multiple catch blocks for each type of exception and the handling of each exception can be customized to what you want by coding it in each of their catch blocks.
Your ExceptionsDemo throws a IOException, your catch in ExceptionsDemo only catches a InsufficientFundsException so it will not be caught in the ExceptionsDemo, it will bubble to the caller, and be caught there, providing there is a catch block to handle said exception, which it does, otherwise you'll have an uncaught exception. It's not been rethrown from ExceptionsDemo, because its not being caught in the first place
try {
// do what you want
} catch (InsufficientFundsException e) {
// catch what you want
} catch (Exception e) {
// catch unexpected errors, if you want (optional)
}
In Java, if I declare and caught an exception, can I handle the exception in a caller anyway? Or it needs not to be caught to handle it by caller?
class A {
void first() throws Exception {
try {
throw new Exception("my exception")
} catch (Exception e) {
log.message("Error in first()", e.getCouse)
throw e
}
}
}
class B {
Result second(A a) {
try {
a.first()
} catch (Exception e) {
log.message("Caught in B class", e.message)
return new Result(result: null, error: e.message)
}
}
second(A a)
}
You can simply rethrow the exception you've caught (obviously the surrounding method has to permit this via its signature etc.). The exception will maintain the original stack trace.
catch (WhateverException e) {
throw e;
}
You can also wrap the exception in another one AND keep the original stack trace by passing in the Exception as a Throwable as the cause parameter:
try
{
...
}
catch (Exception e)
{
throw new YourOwnException(e);
}
Is it any possible way there to write catch block inside a method and call it from finally when an exception occured in try block
Ex:
try
{
int a=0,b=0;
a=b/0;
}
finally
{
callExceptions();
}
}
public static void callExceptions()
{
catch(Exception e)
{
System.out.println(e);
}
}
catch block must follow a try block. It can't stand alone.
And finally block are made to be after the catch.
You wrote an alone catch inside a finally. That doesn't make sense.
The easiest solution is to pass the exception to the method as a parameter:
public static myMethod() {
try
{
int a=0,b=0;
a=b/0;
}
catch (Exception e)
{
callExceptions(e);
}
finally
{
// do what ever you want or remove this block
}
}
public static void callExceptions(Exception e)
{
System.out.println(e);
}
Ways to uses try/catch/finally
1.- when you want to try to use some method, if everything goes well, will continue else one exception will be thrown on catch block.
try {
// some method or logic that might throw some exception.
} catch (ExceptionType name) {
// catch the exception that was thrown.
}
2.- It's the same the first but adding finally block means that the finally block will always be executed independently if some unexpected exception occurs.
try {
// some method or logic that might throw some exception.
} catch (ExceptionType name) {
// catch the exception that was thrown.
} finally {
// some logic after try or catch blocks.
}
3.- try and finally blocks are used to ensure that a resource is closed regardless of whether the try statement completes normally or abruptly. For example:
BufferedReader br = new BufferedReader(new FileReader(path));
try {
return br.readLine();
} finally {
if (br != null) br.close();
}
Referencias Official documentation JAVA for try/catch/finally blocks
On your case:
public static myMethod() {
try {
int a=0,b=0;
a=b/0;
} catch (Exception e) {
callException(e);
}
}
public static void callException(Exception e) {
System.out.println(e);
}
This was too long for a comment so sorry it's not a direct answer to your question (as others have pointed out, that's not possible). Assuming what you're trying to do is define a common way to handle your exception logic in one place, Callable might be a way to go. Something like the following might suffice... Although I'm not going to comment on whether any of it is a good idea...
static E callAndHandle(final Callable<E> callable) {
try {
return callable.call();
} catch (final Exception ex) {
System.out.println(ex);
return null;
}
}
static void tryIt() {
final String result = callAndHandle(() -> {
// Thing which might throw an Exception
return "ok";
});
// result == null => there was an error here...
}
Unfortunately Runnable doesn't declare any Exception in the signature, so if you know it always needs to be void and you don't like the return null; or similar hacks, you'd have to define your own interface to pass in.
I need to handle Exceptions which are raised by Catch block code in Java
Example, to "handle" an Exception:
try
{
// try do something
}
catch (Exception e)
{
System.out.println("Caught Exception: " + e.getMessage());
//Do some more
}
More info see: See: https://docs.oracle.com/javase/tutorial/essential/exceptions/catch.html
However if you want another catch in your try catch, you can do the following:
try
{
//Do something
}
catch (IOException e)
{
System.out.println("Caught IOException: " + e.getMessage());
try
{
// Try something else
}
catch ( Exception e1 )
{
System.out.println("Caught Another exception: " + e1.getMessage());
}
}
Be careful with nested try/catch, when your try catch is getting to complex/large, consider splitting it up into its own method. For example:
try {
// do something here
}
catch(IOException e)
{
System.out.println("Caught IOException: " + e.getMessage());
foo();
}
private void foo()
{
try {
// do something here (when we have the IO exception)
}
catch(Exception e)
{
System.out.println("Caught another exception: " + e.getMessage());
}
}
Instead of cascading try/catch (like in most of the other answers), I advise you to call another method, executing the required operations. Your code will be easier to maintain by this way.
In this method, put a try/catch block to protect the code.
Example :
public int classicMethodInCaseOfException(int exampleParam) {
try {
// TODO
}
catch(Exception e)
{
methodInCaseOfException();
}
}
public int methodInCaseOfException()
{
try {
// TODO
}
catch(Exception e)
{
//TODO
}
}
Do as you would do in an usual try/catch situation :
try{
throw new Exception();
}catch(Exception e1){
try{
throw new Exception();
}catch(Exception e2){
//do something
}
}
You can add new try catch block in your main catch block.
try
{
int b=10/0;
}catch(ArithmeticException e)
{
System.out.println("ArithmeticException occurred");
try
{
int c=20/0;
}catch(ArithmeticException e1)
{
System.out.println("Another ArithmeticException occurred");
}
}
I think the most clean way is to create method which is catching the exceptions occurs in its body. However it can be very dependent to the situation and type of code you are dealing with.
One example of what you are asking about is closing a Stream which is opened in a try-catch-finally block. For example:
package a;
import java.io.BufferedOutputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
public class Main {
public static void main(String[] args) {
OutputStream out = null;
try {
out = new BufferedOutputStream(new FileOutputStream("temp.txt"));
} catch (FileNotFoundException e) {
e.printStackTrace();
//TODO: Log the exception and handle it,
// for example show a message to the user
} finally {
//out.close(); //Second level exception is
// occurring in closing the
// Stream. Move it to a new method:
closeOutPutStreamResource(out);
}
}
private static void closeOutPutStreamResource(OutputStream out){
try {
out.close();
} catch (IOException e) {
// TODO: log the exception and ignore
// if it's not important
// OR
// Throw an instance of RuntimeException
// or one of it's subclasses
// which doesn't make you to catch it
// using a try-catch block (unchecked)
throw new CloseOutPutStreamException(e);
}
}
}
class CloseOutPutStreamException extends RuntimeException{
public CloseOutPutStreamException() {
super();
}
public CloseOutPutStreamException(String message, Throwable cause,
boolean enableSuppression, boolean writableStackTrace) {
super(message, cause, enableSuppression, writableStackTrace);
}
public CloseOutPutStreamException(String message, Throwable cause) {
super(message, cause);
}
public CloseOutPutStreamException(String message) {
super(message);
}
public CloseOutPutStreamException(Throwable cause) {
super(cause);
}
}
Here I illustrated a situation which the second level exception is occurring in the finally block, but the same can apply for the exceptions occur in the catch block.
In my point of view writing methods such as closeOutPutStreamResource can be useful because they are packaging a boiler plate code for handling very common exceptions and they are making your codes more elegant.
Also it would be your choice to catch and log the exception in closeOutPutStreamResource or to throw it to other layers of your program. But it would be more elegant to wrap this unimportant checked exceptions into RuntimeException without a need for catching.
Hope this would be helpful.
You can use try catch block any where in methods or in block, so you can write try catch in catch block as well.
try {
// master try
}catch(Exception e){
// master catch
try {
// child try in master catch
}catch(Exception e1){
// child catch in master catch
}
}//master catch
It's not necessary to have a nested try-catch block when catch block throws Exception as all answers here suggest. You can enclose the caller method with try-catch to handle that Exception.
In Java, if a general exception is caught and rethrown, will outer methods still be able to catch specific exceptions?
In other words, can I do this:
try {
try {
//...
} catch (Exception e) {
//...
throw e;
}
} catch (SpecificException e) {
//...
}
re-throwing an exception does not change anything about it (it's still the same object originally thrown).
While jtahlborn answer is correct, there is one more appreciation: the compiler will see that you are throwing an exception of the generic type (even if at runtime it can be only of the specific class) and will force you to declare the generic exception in the method header.
private void test() throws FileNotFoundException {
try {
throw new FileNotFoundException("Es una exception");
} catch (IOException e) {
throw e; <-- Error because the method only throws
FileNotFoundException, not IOException
}
}
e is indeed FileNotFoundException, but as it is declared as IOException the compiler works with the broader class. What you can do is "cast" the exception.
throw (FileNotFoundException) e;
Eclipse marks the "throw e" in the inner catch as an unhandled exception, BUT it does catch the exception because when I run this it prints "It worked!". Thanks #jtahlborn. Unfortunately this means that there will still need to be an unnecessary try/catch block somewhere.
public class Tester {
public static void main(String[] args) {
try {
try {
throw new SpecificException("Test!");
} catch (Exception e) {
throw e;
}
} catch (SpecificException e) {
System.out.println("It worked!");
}
}
}