How to Access Variable Outside a Try Catch Block

How to access a variable outside a try catch block

The error is that you are not returning anything in the case where an exception is thrown.

try the following:

public boolean checkStatus(){
   boolean result = true;  // default value.
   try{

        InputStream fstream = MyRegDb.class.getClassLoader().getResourceAsStream("textfile.txt");
        // Use DataInputStream to read binary NOT text.
        BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
        String strLine;

        //Read File Line By Line
        strLine = br.readLine();
        // Print the content on the console
        System.out.println (strLine);

        ind.close();
        if(strLine.equals("1")){

            result = false;   
        }else{
            result = true;    
        }

    }catch(Exception e){}
    return result;
}

How can I access a variable from outside the try catch block?

Scope of a variable: As a general rule, variables that are defined within a block are not accessible outside that block.

Lifetime of a variable: Once a variable loses it scope, Garbage collector will takes care of destroying the variable/object. The lifetime of a variable refers to how long the variable exists before it is destroyed.

try {
     byte len = (byte) passLength();
}

In your above example, the variable len is declared inside the try block, its scope is only within the try block and can't be accessed outside the try block.

You should declare the len variable even before the try block, so that it can be accessed in the finally block.

byte len = Byte.MIN_VALUE;  //This value is for dummy assignment
try {
     len = (byte) passLength();
} catch(Exception inputMismatchException) { // Avoid using variable name starts with Capitals
     System.out.println("Error, please input a proper number");
} finally {
     String result = passGen(len, chars);
     System.out.println(result);
}

Hope, this will be helpful :)

Using variable outside of try catch block (Java)

To resolve the compilation error, declare the result variable only before the try-catch block:

List<String> result; 
try( Stream<Path> walk = Files.walk(Paths.get("data"))){
    result = walk.filter(Files::isRegularFile)
            .map(x -> x.toString()).collect(Collectors.toList());
}
catch(Exception e){
    e.printStackTrace();
    result = null;
}

However, note that accessing the result variable after the try-catch block (your result.listiterator() statement) without checking that it's not null may throw a NullPointerException.

You should be asking yourself why you are catching any exception and expecting everything to work fine.

Java how to access a variable outside the try-catch block

You should declare the variable before the try block (in order for it to still be in scope after the try-catch blocks), but give it an initial value :

class factorial{
  public static void main(String[] args){
    int num = 0;
    try {
         num = Integer.parseInt(args[0]);
    }
    catch(Exception e){
        System.out.println(e+" Cannot convert arg to int, exiting..");
    }
    System.out.println(num );

  }
}

how can I access to a variable in try block in other try block?

The author of that post clearly did a mistake there––it happens to all of us.

So, the const declarations are block-scoped, like the docs say:

Constants are block-scoped, much like variables defined using the let statement. The value of a constant cannot change through re-assignment, and it can't be redeclared.

That's why you cannot access it outside of the try-catch block.

To solve the problem:

Either use var instead of const:

try {
  // When declared via `var`, the variable will
  // be declared outside of the block
  var foo = "bar"
} catch (e) {
  console.log(e)
}

try {
  console.log(foo)
} catch (e) {
  console.log(e)
}

Or you can declare the variable outside of the try-catch, using let:

// Maybe it's clearer to declare it with let and 
// assign the value in the first try-catch
let foo;
try {
  foo = "bar"
} catch (e) {
   console.log(e)
}

try {
  console.log(foo)
} catch (e) {
  console.log(e)
}

How to use var - variable outside of try-catch block

Thanks to Evk for the good answer (But in the comments...)
I declare myValue as an object:

 string myValue;
try
{                    
    myValue = from el in keyValueList select el.Value;
}
catch (Exception ex)
{

}

Using variable outside Try-Catch

Your example is a perfect illustration of why writing

catch (Exception){}

is a very bad practice.

When you catch an exception, you are supposed to do something about it. If you do not know what to do with an exception in a particular method of your code, don't catch the exception in that method.

If you always need a customer, even when its retrieval causes an exception, add some code to the catch block to set customer variable to some default object:

try {
    ...
} catch (Exception) {
    customer = Customer.Unknown;
}

This assumes that Customer has a property Unknown of type Customer with some default behavior.

Comment: Needed to warn the upper level of my code. Just, when I create an instance, create it, but warn the arguments where wrong. Could you recommend me some better approach?

Make a factory for validating users while creating them:

class CustomerCreationResult {
    public Customer Customer() { get; set; }
    public CustomerCreationError Error() { get; set; }
}

class CustomerFactory {
    public CustomerCreationResult CreateCustomer(String name, int age) { ... }
}

Now you can create your customers as follows:

var r = myCustomerFactory.CreateCustomer(name, age);
if (r.getError() != null) {
    ... // Present the error
}
Customer customer = r.Customer;
...