I have a java program that does not return the correct answer and I cannot figure out why. here's the code:
public class hello {
public static void main(String[] args) {
int a =5;
doubleNumbers(a);
System.out.println(" 5 doubled is:"+a);
}
private static void doubleNumbers(int a) {
a = 5*2;
}
}
It is my first java program after helloWorld.
Java is pass-by-value, which means that the variables passed to a function are not changed outside of it.
As this is homework I will not show you the solution, but just tell you to return the value of the calculation.
you're not returning anything from your method
change it to
private static int doubleNumbers(int a) {
return a * 2;
}
There are two problems with your code. First you should change the doubleNumbers method to return something, next you should change the print statement to where it is printing the returned value.
for example(in pseudo code, so you have to think about it!):
method doCalculation{
....
return calculated answer
}
main{
....
Print(doCalculation)
}
I would change the method doubleNumbers to return the result of the calculation, so it would look something like this:
private static void doubleNumbers(int a) {
return a*2;
}
And then change the lines in the main method:
int a = 5;
a = doubleNumbers(a);
Also, doubleNumbers would only ever return 10 in the original implementation. You need to use the a variable you passed in, as the above code shows.
primitive types in Java passed by value not by reference. You need Object-type to pass it by reference try this:
private static void doubleNumbers(Integer a) {
a = a*2;
}
There are 2 obvious problems:
doubleNumbers() to any variable. doubleNumbers() does not return a value (replace voidwith int)
public class hello {
public static void main(String[] args)
{
int a =5;
a = doubleNumbers(a);
System.out.println(" 5 doubled is:"+a);
}
private static int doubleNumbers(int a) {
return a*2;
}
}
Each variable has a context, by default limited to the function which uses it.
Your a in the doubleNumbers() function isn't the same as the first one.
You need to return the result, and assign it to your original a variable
A better way will be to change double Numbers() method from void to int so it can be returnable and also instead of printing only a, rather print the method as now it will be doubling the a.
I've also added Scanner so the program don't just double 5 but any number you enter.
public class Hello {
public static void main(String[] args) {
Scanner myScn = new Scanner(System.in);
System.out.println("Please enter a number: ");
int a = myScn.nextInt();
//doubleNumbers(a);
System.out.println(a+ " doubled is:"+doubleNumbers(a));
}
private static int doubleNumbers(int a) {
int x = a*2;
return x;
}
}
