Return type

In computer programming, the return type (or result type) defines and constrains the data type of the value returned from a subroutine or method.[1] In many programming languages (especially statically-typed programming languages such as C, C++, Java) the return type must be explicitly specified when declaring a function.

In the Java example:

public void setShuma(int n1, int n2) {
    Shuma = n1 + n2
}

public int getShuma() {
    return Shuma;
}

the return type is int. The program can therefore rely on the method returning a value of type int. Various mechanisms are used for the case where a subroutine does not return any value, e.g., a return type of void is used in some programming languages:

public void returnNothing()

Returning a value from a method

A method returns to the code that invoked it when it completes all the statements in the method, reaches a return statement, or throws an exception, whichever occurs first.

You declare a method's return type in its method declaration. Within the body of the method, you use the return statement to return the value.

Any method declared void doesn't return a value. It does not need to contain a return statement, but it may do so. In such a case, a return statement can be used to branch out of a control flow block and exit the method and is simply used like this:

return;

If you try to return a value from a method that is declared void, you will get a compiler error.

Any method that is not declared void must contain a return statement with a corresponding return value, like this:

return returnValue;

The data type of the return value must match the method's declared return type; you can't return an integer value from a method declared to return a boolean.

The getArea() method in the Rectangle Rectangle class that was discussed in the sections on objects returns an integer:

    // A method for computing the area of the rectangle
    public int getArea() {
        return width * height;
    }

This method returns the integer that the expression width * height evaluates to.

The getArea method returns a primitive type. A method can also return a reference type. For example, in a program to manipulate Bicycle objects, we might have a method like this:

    public Bicycle seeWhosFastest(Bicycle myBike, Bicycle yourBike,
                                  Environment env) {
        Bicycle fastest;
        // Code to calculate which bike is 
        // faster, given each bike's gear 
        // and cadence and given the 
        // environment (terrain and wind)
        return fastest;
    }

References
  1. Kernighan, Brian W.; Ritchie, Dennis M. (1988). The C Programming Language (2nd ed.). Prentice Hall. ISBN 0-13-110362-8.
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