An Introduction to Using Functions/Methods

An Introduction to Using Functions/Methods
with Examples in Java

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Overview

Functions in Mathematics:
- A mapping between two sets (called the domain and range)
The Role of Functions in Computing:
- Determine the output based on one or more inputs
- Perform some operation based on zero or more inputs

Examples

Using a Trigonometric Function:
- \(o = \tan(\alpha) \cdot a\)
Using the Square Root:
- \(c = \sqrt{a^2 + b^2}\)
- \(l = \sqrt{(x_1-x_2)^2 + (y_1-y_2)^2}\)

What You Need to Know to Use a Function/Method in Java

Examples

The Statement:
- opposite = Math.tan(alpha) * adjacent;
What Was Needed:
- The function belongs to the Math class
- The name of the function is tan
- The function has one double-valued parameter
- The function returns a double
Where You Find What Was Needed:
- Documentation for Math.tan(double)

Examples (cont.)

The Statement:
- c = Math.hypot(a, b);
What Was Needed:
- The function belongs to the Math class
- The name of the function is hypot
- The function has two double-valued parameters
- The function returns a double
Where You Find What Was Needed:
- Documentation for Math.hypot(double, double)

Examples (cont.)

The Statement:
- length = Math.sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));
What Was Needed:
- The function belongs to the Math class
- The name of the function is sqrt
- The function has one double-valued parameter
- The function returns a double
Where You Find What Was Needed:
- Documentation for Math.sqrt(double)

void Functions/Methods

What They Are:
- Functions/methods that don't return anything
Their Role:
- They do something (e.g., change something) but don't need to return anything
An Example:
- Printing/displaying something on the screen

An Example of a void Function/Method

The Statement:
- System.out.println("Start Wearing Purple");
What Was Needed:
- The method belongs to the out object in the System class
- The name of the method is println
- The method has one String parameter
- The method does not return anything (i.e., is void)