How to access local variable outside method in Java

Which variables in the following code segment are local variables?

2022-10-13T08:04:49+00:00 2022-10-13T08:04:49+00:00

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I need to access string stream1 inside anycodings_java method, but its only works on method scope. anycodings_java I already declare its as global variable in anycodings_java class. Please see sample code below :

Admins

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onTaskCompleted() is a callback method. anycodings_java The Toast inside that method doesn't get anycodings_java called until the asynchronous task is anycodings_java completed. But the Toast at the bottom anycodings_java of onCreate() gets called right away, anycodings_java without waiting for onTaskCompleted() to anycodings_java finish. Simply defining a callback anycodings_java method doesn't mean the code will pause anycodings_java right there and wait for it to complete.

So if you want to set the value of anycodings_java stream1, you have to do it from anycodings_java onTaskCompleted(). And if you want to anycodings_java use the value of stream1 later on, anycodings_java you'll have to somehow check that anycodings_java onTaskCompleted() has executed. This anycodings_java could by by calling the method that uses anycodings_java stream1 directly from onTaskCompleted(), anycodings_java or it could be by performing a null anycodings_java check on stream1 before using it.

Asynchronous operations are one of the anycodings_java most difficult subjects in programming. anycodings_java There are a million ways to handle it.

mRahman

2

The problem is not how you are accessing anycodings_java the variable. The problem when you are anycodings_java accessing it. Specifically, in the anycodings_java second toast you are accessing the anycodings_java variable before the onTaskCompleted anycodings_java callback has been called.

Basically, your onCreate method won't be anycodings_java able to make use of variables set by anycodings_java onTaskCompleted because the latter isn't anycodings_java being called until after the onCreate anycodings_java call has returned.

Note that new anycodings_java LowCostVideo.OnTaskCompleted(){...} is anycodings_java actually creating an instance of an anycodings_java anonymous inner class that gets passed anycodings_java to the LowCostVideo instance. That anycodings_java instance's method only gets called when anycodings_java the LowCostVideo object completes a anycodings_java task.

Clearly what you are doing here is just anycodings_java a test. In the "real" code you are anycodings_java going to have to figure out how to do anycodings_java ... whatever it is you are really trying anycodings_java to do ... in another way.

joy

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Scope of a variable is the part of the program where the variable is accessible. Like C/C++, in Java, all identifiers are lexically (or statically) scoped, i.e.scope of a variable can determined at compile time and independent of function call stack. Java programs are organized in the form of classes. Every class is part of some package. Java scope rules can be covered under following categories.

Member Variables (Class Level Scope)

These variables must be declared inside class (outside any function). They can be directly accessed anywhere in class. Let’s take a look at an example: 

• We can declare class variables anywhere in class, but outside methods.
• Access specified of member variables doesn’t affect scope of them within a class.
• Member variables can be accessed outside a class with following rules

Local Variables (Method Level Scope)

Variables declared inside a method have method level scope and can’t be accessed outside the method. 

Note : Local variables don’t exist after method’s execution is over. 

Here’s another example of method scope, except this time the variable got passed in as a parameter to the method: 

The above code uses this keyword to differentiate between the local and class variables.

As an exercise, predict the output of following Java program.  

Output: 

Loop Variables (Block Scope) 
A variable declared inside pair of brackets “{” and “}” in a method has scope within the brackets only.

Output: 

As another example, consider following program with a for loop. 

Output: 

The right way of doing above is, 

Output: 

Let’s look at tricky example of loop scope. Predict the output of following program. You may be surprised if you are regular C/C++ programmer. 

Output :

Note:- In C++, it will run. But in java it is an error because in java, the name of the variable of inner and outer loop must be different.
A similar program in C++ works. See this.

As an exercise, predict the output of the following Java program. 

Q. From the above knowledge, tell whether the below code will run or not.

Output : 

Yes, it will run! 
See the program carefully, inner loop will terminate before the outer loop variable is declared.So the inner loop variable is destroyed first and then the new variable of same name has been created.

Some Important Points about Variable scope in Java:  

• In general, a set of curly brackets { } defines a scope.
• In Java we can usually access a variable as long as it was defined within the same set of brackets as the code we are writing or within any curly brackets inside of the curly brackets where the variable was defined.
• Any variable defined in a class outside of any method can be used by all member methods.
• When a method has the same local variable as a member, “this” keyword can be used to reference the current class variable.
• For a variable to be read after the termination of a loop, It must be declared before the body of the loop.

 This article is contributed by Rishabh Mahrsee. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to . See your article appearing on the GeeksforGeeks main page and help other Geeks.

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