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Trail: Learning the Java Language
Lesson: Classes and Objects
Section: More on Classes
Classes and Objects
Classes
Declaring Classes
Declaring Member Variables
Defining Methods
Providing Constructors for Your Classes
Passing Information to a Method or a Constructor
Objects
Creating Objects
Using Objects
More on Classes
Returning a Value from a Method
Using the this Keyword
Controlling Access to Members of a Class
Understanding Instance and Class Members
Initializing Fields
Summary of Creating and Using Classes and Objects
Questions and Exercises
Questions and Exercises
Nested Classes
Inner Class Example
Summary of Nested Classes
Questions and Exercises
Enum Types
Questions and Exercises
Annotations
Questions and Exercises
Home Page > Learning the Java Language > Classes and Objects
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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 (covered later),
> 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 `area` 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;
> >     }

> ### Returning a Class or Interface

> If this section confuses you, skip it and return to it after you have finished the lesson on interfaces and inheritance.

> When a method uses a class name as its return type, such as `whosFastest` does, the class of the type of the returned object must be either a subclass of, or the exact class of, the return type. Suppose that you have a class hierarchy in which `ImaginaryNumber` is a subclass of `java.lang.Number`, which is in turn a subclass of `Object`, as illustrated in the following figure.

> The class hierarchy for ImaginaryNumber

> Now suppose that you have a method declared to return a `Number`:

> >     public Number returnANumber() {
> >         ...
> >     }

> The `returnANumber` method can return an `ImaginaryNumber` but not an `Object`. `ImaginaryNumber` is a `Number` because it's a subclass of `Number`. However, an `Object` is not necessarily a `Number` — it could be a `String` or another type.

> You can override a method and define it to return a subclass of the original method, like this:

> >     public ImaginaryNumber returnANumber() {
> >         ...
> >     }

> This technique, called covariant return type, means that the return type is allowed to vary in the same direction as the subclass.

> > Note: You also can use interface names as return types. In this case, the object returned must implement the specified interface.

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