Using a String as a Variable at Run Time

How to access a variable set at run time with a string?

INFO is a constant and, if it's declared in the global scope, you can retrieve it with:

Object.const_get "info".upcase 
Object.const_get param[:type].upcase 

Is it possible to create variables at runtime in Java?

Is it possible to create variables at runtime in Java?

The simple answer is No.

Java is a static language and does not support the injection of new variable declarations into an existing compiled program. There are alternatives (in order of decreasing usefulness / increasing difficulty):

• Represent your "variables" as name / value pairs in a Map. Or come up with some other design that doesn't require real dynamic variables.
• Use a scripting language that runs on the JVM and is callable from Java.
• Use some kind of templating mechanism to generate new source code containing the declarations, and compile and load it dynamically.
• Use a byte code manipulation library (e.g. BCEL) to create class files on the fly and then dynamically load them.

The first approach is the best. Java is a static language, and works best if you don't fight it. If this is a problem for you, maybe you are using the wrong language.

The last two are difficult / complicated and have significant performance costs. They are almost certainly not going to help ...

How to change variable name in runtime

Put your buttons in a HashMap<String, Button>, and this way you could name your buttons and rename them as many times as you want. You cannot rename variables in runtime.

Here is an example:

// this will keep the variables this way: [ "btn01" -> buttonObject1, "btn02" -> buttonObject2 ...]
HashMap<String, Button> buttonHashMap = new HashMap<>();

for(int i = 0; i < 10; i++) 
{
    final int buttonInd = i;
    String buttonName = "btn0" + i;
    Button buttonObject = new Button(Integer.toString(i));
    
    buttonHashMap.put(buttonName, buttonObject);

    // The .get(buttonName) gets the specific Button that you need!
    buttonHashMap.get(buttonName).setOnAction(new EventHandler<ActionEvent>() {
        @Override
        public void handle(ActionEvent e) {
            System.out.println("Button pressed " + ((Button) e.getSource()).getText());
            System.out.println("button clicked " + ((Control)e.getSource()).getId());
            lastClickedIndex = buttonInd;
        }
    });
}

Convert string to variable name or variable type

No, this is not possible. This sort of functionality is common in scripting languages like Ruby and Python, but C++ works very differently from those. In C++ we try to do as much of the program's work as we can at compile time. Sometimes we can do things at runtime, and even then good C++ programmers will find a way to do the work as early as compile time.

If you know you're going to create a variable then create it right away:

int count;

What you might not know ahead of time is the variable's value, so you can defer that for runtime:

std::cin >> count;

If you know you're going to need a collection of variables but not precisely how many of them then create a map or a vector:

std::vector<int> counts;

Remember that the name of a variable is nothing but a name — a way for you to refer to the variable later. In C++ it is not possible nor useful to postpone assigning the name of the variable at runtime. All that would do is make your code more complicated and your program slower.

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