Chapter 5—Methods
The Art and Science of
An Introduction
to Computer Science
ERIC S. ROBERTS
Java
Methods
C H A P T E R 5
With method and logic one can accomplish
anything. —Agatha Christie, Poirot Investigates, 1924
CMPU-101
Computer Science I:
Problem-Solving and Abstraction
Fall 2008
Jennifer Walter
(adapted from slides by Eric Roberts)
A Quick Overview of Methods
• You have been working with methods ever since you wrote
your first Java program in Chapter 2. Most of the programs
you have seen have used method calls such as println and
setColor.
• At the most basic level, a method is a sequence of statements
that has been collected together and given a name. The name
makes it possible to execute the statements by just providing
the method name.
• The following terms are useful when learning about methods:
– Invoking a method using its name is known as calling that method.
– A method call is preceded by either this, an object name, or a class
name and . (the dot operator)
– The caller can pass information to a method by using arguments.
– When a method completes its operation, it returns to its caller, on the
line it was called.
– A method can pass information to the caller by returning a result.
Method Calls are Expressions
• Method calls in Java are expressions. Methods that return a
value can be used as terms in an expression just like variables
and constants and those that don’t can be used on their own.
• The Math class in the java.lang package defines several
methods that are useful in writing mathematical expressions.
Suppose, for example, that you n eed to compute the distance
from the origin to the point (x, y), which is given by
x
2 + y
2
You can apply the square root function by calling the sqrt
method in the Math class like this:
double distance = Math.sqrt(x * x + y * y);
Static (Class) Methods
• Recall the keyword static, used when defining named
constants. This keyword is also used when defining certain
methods. When static is used in a method definition, a
method can be called by using the following pattern:
ClassName.methodName(argument list);
• Note that you need to include the name of the class before a
static method name. Methods like Math.sqrt are called
static methods and are defined with the keyword static in
the definition as shown below:
public static double sqrt(double x) {
Static Method calls on the Math Class
Math.abs(x)Returns the absolute value of x
Math.min(x, y)Returns the smaller of x and y
Math.max(x, y)Returns the larger of x and y
Math.sqrt(x)Returns the square root of x
Math.log(x)Returns the natural logarithm of x (loge x )
Math.exp(x)Returns the inverse logarithm of x (e
x
)
Math.pow(x, y)Returns the value of x raised to the y power (x y
)
Math.sin(theta)Returns the sine of theta, measured in radians
Math.cos(theta)Returns the cosine of theta
Math.tan(theta)Returns the tangent of theta
Math.asin(x)Returns the angle whose sine is x
Math.acos(x)Returns the angle whose cosine is x
Math.atan(x)Returns the angle whose tangent is x
Math.toRadians(degrees)Converts an angle from degrees to radians
Math.toDegrees(radians)Converts an angle from radians to degrees
Writing Your Own Methods
• The general form of a method definition is
scope type name(parameter declaration list) {
statements in the method body
}
where scope indicates who has access to the method, type
indicates the return type, n ame is the identifier of the method,
and parameter declaration list is a list of declarations of
variables that are local to the method.
All methods must be defined directly inside the class braces
(do not define methods inside the curly braces of other
methods)
