Update class fields with sequential names

Question

How to update the background color of 15 JTextField during a loop? For example, I own the following JTextField:

txtEsp1
txtEsp2
txtEsp3
...

And I want to create a loop, to set the background of the 15 as white:

for(int i=1;i<15;i++) {
   txtEsp[i].setBackground(Color.WHITE);
}

Answer 1

I understand what you are trying to do, but Java does not work like this. When using txtEsp[i], you are referencing a position i to a vector called txtEsp, and not for the name of the variable in question.

To do this, Java offers a feature called Reflection, which allows you to access the class’s own resources. To pick the variables with the name txtEspN it is necessary to use the following function:

public void colorir() {
    for(Field field : getClass().getDeclaredFields()) { // ou ClasseExemplo.class no lugar de getClass()
        if (field.getName().matches("^txtEsp(1[0-5]|[0-9])$")) {
            ((JTextField) field.get(this)).setBackground(Color.WHITE); // ou ClasseExemplo.class no lugar de this
        }
    }
}

In this case, I used the regular expression ^txtEsp(1[0-5]|[1-9])$ to validate the numbers, but you could also validate the numbers after txtEsp with Integer#parseInt() and check if a number is contained in 1 ≤ N ≤ 15.

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Note:

When using field.get(this), the compiler can do not find the field searched. This is because Java does not allow the use of local variables such as Fields when searching for them. If this happens, you should turn the local variable into a global variable, placing it in the class scope.