Global variable can't store value-CodePudding

I've been trying to input a String value from the user and store it into a global variable. The input works well inside the method where I instance it, but the problem is that if I try to call the global variable from another method, its value is set back to null.

Here's my code for the input:

Object select;
select = JOptionPane.showInputDialog(this, "Choisissez le département : ", "Boîte de dialogue",
JOptionPane.QUESTION_MESSAGE, icone, liste, liste[0]);
this.select = select.toString();

At this point, if I print this.select in the console, its value is properly shown. Now when I call it from elsewhere:

public void afficherInfos() throws IOException {
//some code
d = new Dep(Integer.parseInt(liste.get(Arrays.asList(d.getDeps()).indexOf(this.getSelect()))));
}

It shows an IndexOutOfBoundsException since indexOf(this.getSelect()) returns -1, as the program can't find it in the array. When I print this.getSelect() inside of this method, the console shows null, but I can't see how it is possible to lose the value, as it was correctly instantiated and stored?

CodePudding user response：

i think it seems to be related promotion and type casting i know when we print some instance with console, that instance printed with toString(), but you use this.getSelect() in indexOf

CodePudding user response：

Global variables are the variables that can be accessed anywhere in the java program. Global variables are not technically allowed in Java. Since Java is object-oriented, everything is part of a class. A static variable can be declared, which can be available to all instances of a class. Well, in your case you can use this.getSelect() in indexOf.