Learning Java, 4th Edition

Methods

Methods appear inside class bodies. They contain local variable declarations and other Java statements that are executed when the method is invoked. Methods may return a value to the caller. They always specify a return type, which can be a primitive type, a reference type, or the type void , which indicates no returned value. Methods may take arguments, which are values supplied by the caller of the method.

Here’s a simple example:

    class Bird {
        int xPos, yPos;

        double fly ( int x, int y ) {
            double distance = Math.sqrt( x*x + y*y );
            flap( distance );
            xPos = x;
            yPos = y;
            return distance;
        }
        ...
    }

In this example, the class Bird defines a method, fly(), that takes as arguments two integers: x and y. It returns a double type value as a result, using the return keyword.

Our method has a fixed number of arguments (two); however, methods can have variable-length argument lists, which allow the method to specify that it can take any number of arguments and sort them itself at runtime. We provide more details later in this chapter.

Local Variables

Our fly() method declares a local variable called distance, which it uses to compute the distance flown. A local variable is temporary; it exists only within the scope (the block) of its method. Local variables are allocated when a method is invoked; they are normally destroyed when the method returns. They can’t be referenced from outside the method itself. If the method is executing concurrently in different threads, each thread has its own ...