1. Using java libraries
CGS3416 spring 2019

2. Some built-in functions
System.out.println(); Math.ceil(); Math.pow(a,2);

3. Function Input output Parameters Return values Defined by return type
public void functionName(variableType a, variableType b) {
//internal block of code }
In order to return values, changing the void to int, String, Boolean etc.

4. Java API – Application Program Interface
Library of classes, Java 8 ~ 4240 classes
Developed by experts, well-tested by users
Used by millions of programmers
Part of JDK

5. API Code Reuse A collection of Packages Classes
Interfaces with their respective
methods
Fields
constructors
Included with the JDK
Code Reuse

6. Java.util.Date != java.sql.Date
Packages
Meaningful organization
Security : private, public
Name scoping
Java.util.Date != java.sql.Date

7. Java API: Important Packages
java.lang ~ fundamental classes (primitive types, string, math functions, thread and exceptions)
java.util ~ Data structures (like Linked List, Dictionary and support ; for Date / Time operations).
java.io ~ Reading (from a file)&writing(to a file)
java.net ~ Networking
java.sql ~ Databases

8. Where – Java documentation
Java 8 api

9. 3rd Party APIs

10. Accessing classes in Packages
Same package ~ direct access
Different package
import
Fully-qualified class name ~ rare!

11. Importing Single vs Multiple Classes
Import single class
Explicit import (or Single-type-Import)
import java.util.Scanner;
Import multiple classes
Separate explicit import
*import (or Import-On-Demand): imports all classes in a package
import java.util.*;
Explicit import or * import?
Better clarity with explicit import
Explicit import seems to be preferred
asterisk wildcard characters

12. Fully-qualified Class name
Alternative to import
java.util.Scanner input = new java.util.Scanner(System.in);
Required if using java.util.Date & java.sql.Date

13. java.lang is imported by default

14. Static fields and methods
class – level
java.lang.Math has only static methods
For a static variable or method, we use this format:
className.fieldName // fields Math.PI
className.methodName(arguments) // methods Math.ceil()
Math

15. Example: java.lang.Math
All fields and methods in this class are static
Class Math has two fields, which are common mathematical constants. Sample usage:
double area = Math.PI * radius * radius; // compute area of a circle
Sample calls to static methods from Math

16. java.lang.Math Math.random() Math.abs()
Double between 0.0 & 1.0 (exclusive)
0 <= (int) (Math.random()*5)<5
Random roll dice 1<=(int)(Math.random() * 6) + 1<=6
Math.abs()
Absolute value
Math.abs(-240) = 240

17. java.lang.Math Math.round() Math.ceil() Math.floor()
Nearest long or int based on argument
Math.round(24.8) = 25, Math.round(24.25f) – 24 (int)
Math.ceil()
Smallest double >= argument & equal to integer
Math.ceil(20.1) = 21
Math.floor()
Largest double <= argument & equal to integer
Math.floor(24.8)=24

18. java.lang.Math Math.min()/max() Math.sqrt()
Positive square of a double

19. Demo
Using math function

20. Instance Field and Methods
Create one or more objects from a class
A class is a blueprint for building objects
For a instance variable or method, we use this format:
objectName.fieldName // fields
objectName.methodName(arguments) // methods

21. Example: java.util.Random library
Demo