The BAD and AVOID WHILE LEARNING solution: Move age and math local variables as static fields in the class.
The class will look like this:
public class TestScanner {
static int age;
static int math;
//rest of your class...
//in method grabInput
static void grabInput() {
//comment the variables
//int age, math;
}
}
The code above will work due to the usage of static fields. First understand what static means and be careful when using it.
You should ask yourself the following questions:
- Should I have a method to display the fields of
TestScanner inside the same class?
- Should I create a new instance of
TestScanner just to display the values of another instance of TestScanner?
In case you answer yes to both questions, then you can create a method that receives an instance of TestScanner and prints its contents. This is how your class will look like:
public class TestScanner {
//Note: they're not static anymore (yay!)
int age;
int math;
public static void main (String args[]) {
TestScanner disInput = new TestScanner();
TestScanner gInput = new TestScanner();
gInput.grabInput();
//note that now we need to pass the instance of TestScanner
//in order to print its contents
disInput.displayInput(gInput);
}
//method for display purposes
void displayInput(TestScanner testScanner) {
System.out.println("Scanner Input here: ");
System.out.println("What is my age: ");
System.out.println(testScanner.age);
System.out.println("What is 2 +2: ");
System.out.println(testScanner.math);
}
void grabInput() {
Scanner stdin = new Scanner(System.in);
System.out.println("What is my age: ");
this.age = stdin.nextInt();
System.out.println("What is 2 +2: ");
this.math = stdin.nextInt();
}
}
Now ask yourself: do I need all this? Is this a good design? Can I perform changes easily or will it take more time and effort to, for example, add a new variable, fill it and display it?
The main problem here is called cohesion. This is, the degree of functionalities within a class. As you can see, TestScanner itself has many responsibilities:
- Store
age and math
- Read it from user input
- Display the data to the user
A better approach will be to separate these functionalities in two classes:
Person (or another name) that will store the data from user input. Based on the names of age and math fields, I thought a proper name of the class could be Person. This class will be in charge to store the data and provide it for different usage e.g. store user input and then use it for display purposes.- A
TestScanner class where you will test the usage of Scanner to read the data from user input and display data to user.
The design will look like this:
class Person {
private int age;
private int math;
public Person(int age, int math) {
this.age = age;
this.math = math;
}
public int getAge() {
return this.age;
}
public int getMath() {
return this.math;
}
//setters avoided for this case
}
class TestScanner {
Scanner scanner;
public TestScanner(Scanner scanner) {
this.scanner = scanner;
}
public Person grabInput() {
System.out.println("What is my age: ");
int age = stdin.nextInt();
System.out.println("What is 2 +2: ");
int math = stdin.nextInt();
return new Person(age, math);
}
public void displayInput(Person person) {
System.out.print("My age: ");
System.out.println(person.getAge());
System.out.print("My value of 2 +2: ");
System.out.println(person.getMath());
}
public static void main(String[] args) {
TestScanner testScanner = new TestScanner(new Scanner(System.in));
Person person = testScanner.grabInput();
testScanner.displayInput(person);
}
}
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