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Catching an error that I dont want to catch

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)
}

How to catch Exceptions occured in Catch block in Java

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.

Using FindBugs in eclipse

I have been using Find Bugs in Eclipse and I can not figure out why some of the bugs are coming up or how to fix them. Any ideas or help would be great!
The first bug is (Bug: Exception is caught when Exception is not thrown in banking.primitive.core.ServerSolution.saveAccounts()):
} catch (Exception e) {
System.out.println(e.getMessage());
e.printStackTrace();
The second bug is (Bug: Exception is caught when Exception is not thrown in banking.primitive.core.ServerSolution.saveAccounts()):
out.writeObject(accountMap.get(i));
I tried to change it to :
out.writeObject(accountMap.get(Integer.toString(i)));
The third bug is (Bug: Exception is caught when Exception is not thrown in banking.primitive.core.ServerSolution.saveAccounts()):
} catch (Exception e) {
e.printStackTrace();
throw new IOException("Could not write file:" + fileName);
For the first bug this is with my try block as well. I am lost. I tried to follow you post below, but I am confused. Sorry, I am very new!
public ServerSolution() {
accountMap = new HashMap<String,Account>();
File file = new File(fileName);
ObjectInputStream in = null;
try {
if (file.exists()) {
System.out.println("Reading from file " + fileName + "...");
in = new ObjectInputStream(new FileInputStream(file));
Integer sizeI = (Integer) in.readObject();
int size = sizeI.intValue();
for (int i=0; i < size; i++) {
Account acc = (Account) in.readObject();
//CST316 TASK 1 CHECKSTYLE FIX
if (acc != null) {
accountMap.put(acc.getName(), acc);
}
}
}
} catch (Exception e) {
System.out.println(e.getMessage());
e.printStackTrace();
} finally {
if (in != null) {
try {
in.close();
} catch (Throwable t) {
t.printStackTrace();
}
}
}
}

See FindBugs Bug Description:
This method uses a try-catch block that catches Exception objects, but Exception is not thrown within the try block, and RuntimeException is not explicitly caught. It is a common bug pattern to say try { ... } catch (Exception e) { something } as a shorthand for catching a number of types of exception each of whose catch blocks is identical, but this construct also accidentally catches RuntimeException as well, masking potential bugs.
A better approach is to either explicitly catch the specific exceptions that are thrown, or to explicitly catch RuntimeException exception, rethrow it, and then catch all non-Runtime Exceptions, as shown below:
try {
...
} catch (RuntimeException e) {
throw e;
} catch (Exception e) {
... deal with all non-runtime exceptions ...
}

Why Findbugs cannot detect my code error?

I have read the bug detectors in findbugs website, http://findbugs.sourceforge.net/bugDescriptions.html
I want to write a test code and use Findbugs to detect the REC error.
But the findbugs cannot. Why? Could you help me to solve this?
Thanks,
Below is the description in Findbugs.
REC: Exception is caught when Exception is not thrown (REC_CATCH_EXCEPTION)
This method uses a try-catch block that catches Exception objects, but Exception is not thrown within the try block, and RuntimeException is not explicitly caught. It is a common bug pattern to say try { ... } catch (Exception e) { something } as a shorthand for catching a number of types of exception each of whose catch blocks is identical, but this construct also accidentally catches RuntimeException as well, masking potential bugs.
A better approach is to either explicitly catch the specific exceptions that are thrown, or to explicitly catch RuntimeException exception, rethrow it, and then catch all non-Runtime Exceptions, as shown below:
try {
...
} catch (RuntimeException e) {
throw e;
} catch (Exception e) {
... deal with all non-runtime exceptions ...
}
My code is:
public static void test1(){
int A[] = {1,2,3};
int result = 5/0;//divided by 0
int arrOut = A[0]+A[4];//index out of bound
System.out.println(arrOut);
System.out.println(result);
try {
} catch (RuntimeException e) {
// TODO: handle exception
System.out.println("Runtimeex throw");
throw e;
} catch (Exception e) {
// TODO: handle exception
System.out.println("An try error occurred: 0 cannot be divided");
}
}

The try is where the exception occur that you want to catch. However, since it is occurring out of the try block, the exception is not caught by the catch part, which is why FindBugs reporting it as a useless try {...} catch {...} code. The proper code should be as follows.
int A[] = {1,2,3};
try {
int result = 5/0;//divided by 0
int arrOut = A[0]+A[4];//index out of bound
System.out.println(arrOut);
System.out.println(result);
} catch (RuntimeException e) {
// TODO: handle exception
System.out.println("Runtimeex throw");
throw e;
} catch (Exception e) {
// TODO: handle exception
System.out.println("An try error occurred: 0 cannot be divided");
}
}

In Java, if a general exception is caught and rethrown, will outer methods still be able to catch specific exceptions?

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!");
}
}
}