why is the output 0.0 if I write the following code? It seems to me like it wouldn't read the variable x inside my class Car.
public class Car {
double x = 2;
double y;
double v = x * y;
public Car(double y) {
this.y = y;
}
public static void main(String[] args) {
Car car = new Car(100);
System.out.println(car.v);
}
}//end of class
The v is being calculated before the y is set in the constructor, so it will always equal 2*0, so 0.
You can do the v calculation inside the constructor instead.
public class Car {
double x = 2;
double y;
double v;
public Car(double y) {
this.y = y;
v = x * y;
}
}
your double v = x * y line is being done on instantiation of a car object, when x is 2 and y is unititialized (0). You need to move that line into the constructor if you want it to update with the proper value.
I have included some System.out inside the constructor to get the flow of the execution.
Here, the value of v is already assigned with value of x and y where x = 2 and y = 0.0.
So,you can modify your code as below:
Code:
Car.java
public class Car {
double x = 2;
double y;
double v;
public Car(double y) {
System.out.println("Inside constructor");
System.out.println("value of v here:" + v);
this.y = y;
v = x * y;
System.out.println("value of v now:" + v);
}
}
Test.java
public class Test {
public static void main(String[] args) {
Car car = new Car(100);
System.out.println(car.v);
}
}
Output:
Inside constructor
value of v here:0.0
value of v now:200.0
200.0
