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Methods

In Java, functions and procedures are called methods. Methods are declared as follows: class Turtle {

          // Attribute declarations, as above

public void jumpTo(int newX, int newY) { x = newX;

y = newY; }

public int getX() { return x;

} }

This example contains two methods. The first is called jumpTo and has two integer param- eters, newX and newY.

The second method is called getX, has no parameters, and returns an integer. Note that the empty pair of parentheses must be present.

Both method declarations begin with the keyword public, to make sure they can be accessed from other classes. (It is however possible to declare methods private or pro- tected, which can be useful for internal methods which should not be used from other classes.)

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Before the method’s name, a type is written to indicate the method’s return type. The jumpTo method does not return a value (i.e., it is a procedure, not a function). For this rea- son, it is declared as void (meaning ‘nothing’). The getX method returns an integer, so it is declared as int


The Structure of a Method

A method is just a chunk of code that does a particular job. But methods are set out in a certain way. You have a method header, and a method body. The header is where you tell Java what value type, if any, the method will return (an int value, a double value, a string value, etc). As well as the return type, you need a name for your method, which also goes in the header. You can pass values over to your methods, and these go between a pair of round brackets. The method body is where you code goes.

The Java method header

The method's return type goes first, which is an int type in the code above. After the method type, you need a space followed by the name of your method. We've called the one above total. In between a pair of round brackets we've told Java that we will be handing the method a variable called aNumber, and that it will be an integer.

To separate this method from any other code, you need a pair of curly brackets. Your code for the method goes between the curly brackets. Note the word return in the method above. This is obviously the value that you want to return from your method, after your code has been executed. But it must be of the same type as the return type in the method header. So the return value can't be a string if you started the method with int total.

Sometimes you don't want Java to return anything at all. Think of Trim in the previous section. You may only want the Trim method to get on with its job, and not return anything to you. A method that doesn't return any value at all can be set up with the word void. In which case, it doesn't need thereturn keyword. Here's a method that doesn't return a value:

A void method in Java

All the method above does is to print some text. It can just get on with its job, so we've set it as a void method. There's no return value.

Methods don't need to have values passed to them. You can just execute some code. Here's a void method without any values being passed over:

A void method with no parameters

And here's an int method that has no values being passed:

A Java  int method

As you can see, the round brackets are empty in both methods. But they are still needed. Miss the round brackets out and you'll get an error message.

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