Programming what is a method

The method definition specifies the names and types of any parameters that are required. When calling code calls the method, it provides concrete values called arguments for each parameter. The arguments must be compatible with the parameter type but the argument name if any used in the calling code doesn't have to be the same as the parameter named defined in the method. For example:. By default, when an instance of a value type is passed to a method, its copy is passed instead of the instance itself.

Therefore, changes to the argument have no effect on the original instance in the calling method. To pass a value-type instance by reference, use the ref keyword. For more information, see Passing Value-Type Parameters. When an object of a reference type is passed to a method, a reference to the object is passed.

That is, the method receives not the object itself but an argument that indicates the location of the object. If you change a member of the object by using this reference, the change is reflected in the argument in the calling method, even if you pass the object by value.

You create a reference type by using the class keyword, as the following example shows:. Now, if you pass an object that is based on this type to a method, a reference to the object is passed.

The example does essentially the same thing as the previous example in that it passes an argument by value to a method. But, because a reference type is used, the result is different. The modification that is made in ModifyObject to the value field of the parameter, obj , also changes the value field of the argument, rt , in the TestRefType method. The TestRefType method displays 33 as the output. For more information about how to pass reference types by reference and by value, see Passing Reference-Type Parameters and Reference Types.

Methods can return a value to the caller. If the return type the type listed before the method name is not void , the method can return the value by using the return keyword. A statement with the return keyword followed by a value that matches the return type will return that value to the method caller. The value can be returned to the caller by value or, starting with C 7. Values are returned to the caller by reference if the ref keyword is used in the method signature and it follows each return keyword.

For example, the following method signature and return statement indicate that the method returns a variable named estDistance by reference to the caller. The syntax is the set of rules established in a language to write the code, in figure 3 we see possible syntax of a method,. We have the structure of a public method that does not require parameters and does not return parameters.

We worked on this script in video 4 of the series. We open and close parentheses indicating that this method does not need parameters. The beginning and end of the method is indicated using keys.

Inside will be all method instructions. Once the method is defined we can make it run from any part of the script, we can even invoke it from other scripts. To invoke this method we write its name and open and close parentheses, we close the instruction with semicolon. By doing this we are achieving that all the instructions of the method are executed.

Notice how the names of the methods are already helping us to understand what is going on. At the beginning of the game the character should be placed randomly. In the upper right corner of figure 3 we have the structure of a method that does not return parameters but does require them to work. This method requires two parameters to work: an integer value m that will indicate the minutes of the timer and an integer value s that will indicate the seconds.

The second is that parameters are entered within parentheses and separated by comma. In both scripts I used confusing names m and s on purpose so that in the future, when we talk about contexts, we can analyze them. The parameter numOfTimes is assigned the value 1 on the first call, and 3 on the second. Just like when calling the predefined method System. If an expression is used as a parameter for a method, the expression is evaluated prior to the method call.

Above, the expression evaluates to 3 and the final method call is of the form greet 3 ;. A method can be defined with multiple parameters. When calling such a method, the parameters are passed in the same order. As a method is called the values of its parameters are copied. In practice, this means that both the main method and the method to be called can use variables with the same name. However, changing the value of the variables inside the method does not affect the value of the variable in the main method that has the same name.

Let's examine this behavior with the following program. Beneath, you'll find the same program visualized step-by-step. Changing the values of the variables in the method printNumbers does not affect the values in the main method, even though they have the same names. So, method parameters are distinct from the variables or parameters of other methods, even if they had the same name. As a variable is passed to a method during a method call, the value of that variable gets copied to be used as the value of the parameter variable declared in the method definition.

Variables in two separate methods are independent of one another. To further demonstrate this point, let's consider the following example. We define a variable called number in the main method. That variable is passed as a parameter to the method incrementByThree.

The value of the variable 'number' in the main program: 1 The value of the method parameter 'number': 1 The value of the method parameter 'number': 4 The value of the variable 'number' in the main program: 1. When the variable number is incremented inside the method, there's no issue. This, however, is not reflected in the number variable of the main program. The number variable living in the main program is different from the number variable of the method.

The parameter number is copied for the method's use, i. The variable number inside the method incrementByThree exists only for the duration of the method's execution and has no relation to the variable of the same name in the main program. Log in to view the quiz. The definition of a method tells whether that method returns a value or not. If it does, the method definition has to include the type of the returned value. Otherwise the keyword void is used in the definition. The methods we've created so far have been defined with the keyword void , meaning that they have not returned values.

The keyword void means that the method returns nothing. If we want the method to return a value, the keyword must be replaced with the type of the return variable. In the following example, there is a method called alwaysReturnsTen which returns an integer-type int variable in this case the value To actually return a value, we use the command return followed by the value to be returned or the name of the variable whose value is to be returned.

The method defined above returns an int -type value of 10 when called. For the return value to be used, it must be stored in a variable. This is done the same way as regular value assignment to a variable, by using an equals sign. The return value of the method is placed in an int type variable as with any other int value. The return value can also be used in any other expression. When execution inside a method reaches the command return , the execution of that method ends and the value is returned to the calling method.

The lines of source code following the command return are never executed. If a programmer adds source code after the return to a place which can never be reached during the method's execution, the IDE will produce an error message. The next method works since it is possible to reach every statement in it — even though there is source code below the return command.

If a method has the form public static void nameOfMethod it is possible to return from it — in other words, to stop its execution in that place — with the return command that is not followed by a value.

For instance:. Defining variables inside methods is done in the same manner as in the "main program". The following method calculates the average of the numbers it receives as parameters. Variables sum and avg are used to help in the calculation.

Variables defined in a method are only visible inside that method. In the example above, this means that the variables sum and avg defined inside the method average are not visible in the main program.

Popular Examples Check prime number. Print the Fibonacci series. Print Pyramids and Patterns. Multiply two matrices. Find the standard deviation. Reference Materials String. Start Learning Java. Explore Java Examples. Related Topics Java Method Overloading. Java Methods In this tutorial, we will learn about Java methods, how to define methods, and how to use methods in Java programs with the help of examples.

Java Methods A method is a block of code that performs a specific task. You can create two methods to solve this problem: a method to draw the circle a method to color the circle Dividing a complex problem into smaller chunks makes your program easy to understand and reusable. In Java, there are two types of methods: User-defined Methods : We can create our own method based on our requirements.

Standard Library Methods : These are built-in methods in Java that are available to use. Let's first learn about user-defined methods. If the method does not return a value, its return type is void. However, the complete syntax of declaring a method is modifier static returnType nameOfMethod parameter1, parameter2, To learn more, visit Java Access Specifier. For example, the sqrt method of standard Math class is static.

Hence, we can directly call Math. We can pass any number of arguments to a method. Calling a Method in Java In the above example, we have declared a method named addNumbers. Here's is how we can call the addNumbers method.