java-mod-1-scope-lab's Introduction

Scope Lab

Learning Goals

Fix scope issues

Instruction

Modify the sample code in the previous section such that we can display the integer value we have assigned based on the value of the flag variable.

public class StudentGame {
    public static void main(String[] args) {
        boolean flag = false;
        if (flag) {
            // do something when flag is true
            int numberWhenFlagIsTrue = 12;
        } else {
            // do something else when flag is false
            int numberWhenFlagIsFalse = 5;
        }
        System.out.println(numberWhenFlagIsTrue); // <- this will not work because numberWhenFlagIsTrue is not in scope
    }
}

Walkthrough

In order to make this work, we have to make two changes:

Separate the declaration and the assignment of the integer variable we use to track the number value we assign
Use a single variable for both the true case and the false case

public class StudentGame {
    public static void main(String[] args) {
        boolean flag = false;
        int number;
        if (flag) {
            // do something when flag is true
            number = 12;
        } else {
            // do something else when flag is false
            number = 5;
        }
        System.out.println(number);
    }
}

Now that my number variable is declared inside the method scope, I can access it from both the scope of the if statement and the scope of the else statement, and I can display its value in the terminal when I'm done with the conditional logic.

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