为什么不满足条件时我无法获得-1的返回值？

Question

why am i not able to get the return value of -1 when the condition is not met?

package calcfeetandinchestocm;

public class Calcfeetandinchestocm {

    public static void main(String[] args) {
        calcFeetAndInchesToCentimeters(4, 12);

        calcFeetAndInchesToCentimeters(-0.5);
    }

    public static int calcFeetAndInchesToCentimeters(double feet, double inches) {

        if (feet >= 0) {
            System.out.println("feet are " + feet + \
                               " and its equal centimeters are " + feet * 12);

        }

        if (inches >= 0 && inches <= 12) {
            System.out.println("inches are " + inches + \
                               "and its equal centimeters are " + inches * 2.45);
        }

        return -1;
    }

    public static int calcFeetAndInchesToCentimeters(double inches) {
        if (inches >= 0) {
            System.out.println("inches are " + inches + \
                          "and its equal centimeters are " + inches * 2.45);
        }
        return -1;
    }

}

Answer 1

I'll address your question first.

why am i not able to get the return value of -1 when the condition is not met?

You do not assign the result of the method call to a variable, so it's unclear how you recognize that you're not getting -1. In fact your methods as you have written them will always return -1 since that is the only return statement you have within the method body.

If you were to assign the result to a variable like this:

int centimeters = calcFeetAndInchesToCentimeters(4, 12);
System.out.println("4 feet 12 inches converted to centimeters is: "+centimeters);

The call to System.out.println above would output 4 feet 12 inches converted to centimeters is: -1

There are a few other problems with your code:

1. You are not correctly calculating the result of the conversion.
2. You have a second method with the same name as the first but with fewer parameters and you're repeating part of the logic in the first method.

To address #1 - one foot is 30.48cm so obviously this line is incorrect:

System.out.println("feet are " + feet + \
                           " and its equal centimeters are " + feet * 12);

Furthermore one inch is 2. 5 4cm so your other calculation is also incorrect:

System.out.println("inches are " + inches + \
                           "and its equal centimeters are " + inches * 2.45);

I think it's probably obvious after what I said in the beginning, but you're also not returning the result of your calculation which is what I believe you intend to do. You need to convert feet to centimeters and inches to centimeters then return the sum of those two results.

To address #2 - your second method should probably not have the same name as it does not take a feet parameter at all.

Something like this would be more accurate:

public static int calcInchesToCentimeters(double inches)

Inside of this method you should not repeat the logic you have already written earlier in the code, instead just call your first method with 0 as the number of feet and pass the number of inches.

public static int calcInchesToCentimeters(double inches){
    return calcFeetAndInchesToCentimeters(0, inches);
}

Lastly some further reading I would suggest for you:

Java Tutorial: Returning a Value from a Method

The DRY Principle

Answer 2

You have to set a variable equal to the function or do a system out print with the function as it's argument like:

System.out.print(calcFeetAndInchesToCentimeters(4, 12));

or

x = calcFeetAndInchesToCentimeters(4, 12);
System.out.print(x);

Answer 3

Here in your code, it dose not depend on condition so either your condition is true or false it returns always -1 so, you just need to grab return value from function. Like,

int result = calcFeetAndInchesToCentimeters(4, 12);
System.out.println("Result is " + result);

it surely print -1.