Learning Java

Methods

Methods appear inside class bodies. They contain local variable declarations and other Java statements that are executed by a calling thread when the method is invoked. Method declarations in Java look like ANSI C-style function declarations with two restrictions: a method in Java always specifies a return type (there’s no default). The returned value can be a primitive type, a reference type, or the type void, which indicates no returned value. A method always has a fixed number of arguments. The combination of method overloading and true arrays lessens the need for a variable number of arguments. These techniques are type-safe and easier to use than C’s variable-argument list mechanism.

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.

Local Variables

The 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 of its method. Local variables are allocated and initialized 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 ...