Java Reference
In-Depth Information
Java syntax: Procedure call (or procedure invocation)
procedure-name ( argument , ... , argument ) ;
Each argument is an expression whose type is the same as or narrow-
er than the corresponding parameter of the procedure being called.
Example: drawRect(5, 10, 20, 30);
Purpose: We can view execution of a procedure call as doing what the
specification of the procedure call says (with the parameters in the
specification replaced by the arguments of the call).
/** = the larger of x and y */
public int larger( int x, int y) { … }
You can tell that this is a function because of the type int after public , which
indicates the type of value that the function produces. The specification indicates
that a call to the function evaluates to the larger of the two parameters x and y .
The procedure call
We now explain how the method specification and method header are used in
writing a method call , or method invocation , as it is sometimes called.
/** Draw a line from pixel (x1, y1) to pixel (x2, y2) . */
public void drawLine( int x1, int y1, int x2, int y2) {
Suppose we want to use procedure drawLine , shown above, to draw a line
in the graphics window from pixel (20, 20) to pixel (80, 40) . Notice that if x1 ,
y1 , x2 , and y2 in procedure drawLine are replaced with 20 , 20 , 80 , and 40 , the
drawLine spec says that the procedure will do exactly what we want:
Draw a line from pixel (20, 20) to pixel (80, 40)
To write this statement in Java, we use a form of statement called the pro-
cedure call . Here is an example:
drawLine(20, 20, 80, 40);
This procedure call consists of:
The name of the procedure, drawLine .
A list of four integers, separated by commas and enclosed in parentheses;
these are the arguments of the call.
A semicolon.
A method call has one argument for each parameter of the method. The first
argument corresponds to the first parameter, the second argument to the second
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