1. Java Programming 
Anahita Mohseni Kabir
1/1
04/08/2016

2. Java Language Platform independent programming language → portable
Similar to C++ in syntax
Object-oriented
Concurrent programming → multi-threading

3. Features Type checking Garbage collection
No direct access to memory (no pointers)
Person[] femaleFamily = family;
for (int i=0;i<family.length;i++){
if (family[i].getGender() == 'm'){ ; }
for file in os.listdir(dir+"new/"):
if file.endswith(".bag"):
StartTime = None
CSVFile = open(dir,'w')
bag = rosbag.Bag(dir+"new/"+file)
for topic, msg, t in …
bag.close()
Java
Python

4. Java Bytecode Locally or through network
How it works?
Java Source (.java)
Java Compiler
Java Bytecode (.class)
Java Bytecode Locally or through network
Class loader/
Bytecode Verifier
Java Class Libraries
Java Interpreter
Just in Time Compiler
Runtime System
Operating System
Hardware
Java Virtual Machine or

5. Object Oriented Design (OOD)

6. Object Oriented Design (OOD)
Structured-Programming: data is separate from program instructions
Object-oriented programming: combines data and program instructions
What is an object:
Contains attributes and behavior
Attributes:
Name
Age
Height
Weight
Gender …
Behaviors:
Walking
Talking
Texting
Person

7. OOD: Encapsulation
Encapsulation: objects hide their methods (functions) and data (variables)
In java, encapsulation is enabled by using access modifiers such as: public, private and protected

8. OOD: Inheritance Person Teacher Student
Inheritance: each subclass inherits all variables of its superclass
Removes duplicated code
Subclass can override some of the functions of its superclass
Subclass
Superclass
Person
Teacher
Student
Attributes:
Name
Age
Height
Weight
Gender …
Behaviors:
Walking
Talking
Texting …

9. OOD: Polymorphsim
Polymorphism: objects that belong to the same branch of a hierarchy, when told to do the same thing, can manifest that behavior differently
Java uses inheritance/interfaces to implement polymorphism
Creature
Person
Animal
Cat
Dog
Creatures:
A human
A cat
A dog
Talk()

11. Java Syntax & Programming Paradigm

12. Reserved Words abstract float super assert for switch boolean goto
synchronized
byte if
this
break
implements
throw
import
throws
case
instanceof
transient
catch
int
try
char
interface
void
class
long
volatile
const
native
while
continue
new
default
package
false do
private
true
double
protected
null
else
public
enum
return
extends
short
final
static
finally
strictfp

13. Primitive Types
boolean, char, byte, short, int, long, float, double, …
Better performance in comparison to their JDK counterpart (non-primitives)
Primitive values are initialized to zero or false
Non-primitive values (objects) are initialized to NULL
Primitive
JDK counterpart
boolean
java.lang.Boolean
int
java.lang.Integer
double
java.lang.Double …

14. Class (Non-primitive Types)
A class is a blueprint for a discrete entity (object) that contains attributes and behavior → Object definition
Each class definition is a separate .java file
Name of the file must match class/object name
class Person{ } …
Person.java

15. Class Definition

16. … package edu.wpi.lecture.personExample; import java.lang.Math;
public class Person implements Creature{
private String name;
private float height;
private float weight; …
public Person(String name, int age, float height, float weight, char gender) {
this.name = name;
this.age = age;
this.height = height;
this.weight = weight;
this.gender = gender; }
public double computeBodyMassIndex() throws ArithmeticException{
if (this.height != 0){
double bmi = this.weight / Math.pow((double)this.height,2);
System.out.print(this.name + "'s " + "BMI is: " + bmi);
return bmi;
else{
throw new ArithmeticException("Division by zero!");

17. Packages
A Java package is a mechanism for providing a namespace— an area inside of which names are unique, but outside of which they might not be.
Each dot-separated part is stored as a folder
package edu.wpi.lecture.personExample;
import java.lang.Math;
public class Person implements Creature{
private String name;
private float height;
private float weight; …

18. Import statements
Any non-trivial class uses other classes for some functionality, and the import statement is how you tell the Java compiler about them
package edu.wpi.lecture.personExample;
import java.lang.Math;
public class Person implements Creature{ …
public double computeBodyMassIndex() throws ArithmeticException{
if (this.height != 0){
double bmi = this.weight / Math.pow((double)this.height,2);
The import is needed if the class is in another package
???

19. How to Make a Project?
Project name
Package name
Classes

20. Encapsulation Access Modifiers
Maintain a boundary between the object’s state and behavior and the outside world
Use private, public, protected or no modifier
Members of a class access levels:

21. … package edu.wpi.lecture.personExample; import java.lang.Math;
public class Person implements Creature{
private String name;
private float height;
private float weight; …
public Person(String name, int age, float height, float weight, char gender) {
this.name = name;
this.age = age;
this.height = height;
this.weight = weight;
this.gender = gender; }
public double computeBodyMassIndex() throws ArithmeticException{
if (this.height != 0){
double bmi = this.weight / Math.pow((double)this.height,2);
System.out.print(this.name + "'s " + "BMI is: " + bmi);
return bmi;
else{
throw new ArithmeticException("Division by zero!");

22. Variables Define the state of a class Have primitive or class type
Can be private, public or protected
public
package edu.wpi.lecture.personExample;
import java.lang.Math;
public class Person implements Creature{
private String name;
private float height;
private float weight; …

23. Methods A class's methods define its behavior
Takes some parameters, performs some computations, and then optionally returns a value/object
Two main categories:
Constructors: used only to create an instance of a class
All the others: used for any application behavior

24. Method’s Signature public double computeBodyMassIndex(){
accessSpecifier
returnType
name
argumentList
public double computeBodyMassIndex(){
double bmi = weight / Math.pow((double)height,2);
System.out.print(this.name + "'s " + "BMI is: " + bmi);
return bmi; }
Methods can have the same name but they should differ in their argument list (the right method is selected at runtime)

25. Constructor Methods Specify how to instantiate a class
Default constructor: if you don't provide a constructor, the compiler provides one for you, called the default (or no- argument) constructor
Have the same name as the class
Don’t have returnType
public class Person implements Creature{ …
public Person(String name, int age, float height, float weight, char gender) {
this.name = name;
this.age = age;
this.height = height;
this.weight = weight;
this.gender = gender; }

26. Objects vs. Classes
An object is created by calling one of the constructor methods of a class
Each object is an instance of a class
The dot operator allows you to access public/protected variables and methods of a class
Objects are passed by reference – not value!
Person anahita = new Person("Anahita",24,0,90,'f');
double bmi = anahita.computeBodyMassIndex();

27. Inheritance Inheritance Removes duplicated code
Superclass – subclass, parent – child
Java only supports single inheritance: any class can have at most one superclass, but a class can have any number of subclasses
java.lang.Object is at the top of this hierarchy: this is assumed for all the classes
equals()
toString()
clone()
Wait()
Creature
(Interface)
Person
Animal
Cat
Dog

28. Creature (Interface) Person Animal Cat Dog
Explicitly call superclass’s constructor other than the default constructor
package edu.wpi.lecture.personExample;
public class Cat extends Animal{
double meanness = 1.0;
public Cat(int numOfLegs,double meanness) {
super(numOfLegs);
this.meanness = meanness; }
@Override
public String talk() {
return "Meow Meow!";
Creature
(Interface)
Person
Animal
Cat
Dog
package edu.wpi.lecture.personExample;
public class Animal implements Creature{
int numOfLegs = 4;
public Animal(int numOfLegs) {
super();
this.numOfLegs = numOfLegs; }
@Override
public String talk() {
return "Random animal sounds!";

29. Interfaces
An interface specifies the behavior that the implementation provides, but not how it is accomplished
A single class can implement as many interfaces as it wants to

30. package edu.wpi.lecture.personExample; public interface Creature {
Animal
Cat
Dog
package edu.wpi.lecture.personExample;
public interface Creature {
public String talk(); }
package edu.wpi.lecture.personExample;
public class Animal implements Creature{
int numOfLegs = 4;
public Animal(int numOfLegs) {
super();
this.numOfLegs = numOfLegs; }
@Override
public String talk() {
return "Random animal sounds!";

31. Polymorphism package edu.wpi.lecture.personExample;
import java.util.ArrayList;
import java.util.List;
public class TestPoly {
public static void main(String[] args) {
Person anahita = new Person("Anahita",24,0,90,'f');
Animal cat = new Cat(4,0.9);
List<Creature> creatures = new ArrayList<Creature>();
creatures.add(anahita);
creatures.add(cat);
for (Creature creature:creatures){
System.out.println(creature.talk()); }
Polymorphism

32. Basics

33. Operators Operators Arithmetic operators:
Unary operators: only one operand is needed
Binary operators: two operands are needed
Arithmetic operators:
++, -- (higher priority)
*, /, %, +=, -=, *=, /=
+, -
Example: a + b % d – c * d / ++b
Relational and conditional operators
Boolean operators: &&, ||, ! (Unary)
==, !=, >=, <=, >, <

34. Statements and blocks Statements terminate with ;
A block is a compound statement enclosed in curly brackets
Blocks may contain other blocks and define scope of the variables
public double computeBodyMassIndex() throws ArithmeticException{
if (this.height != 0){
double bmi = this.weight / Math.pow((double)this.height,2);
System.out.print(this.name + "'s " + "BMI is: " + bmi);
return bmi; }
else{
throw new ArithmeticException("Division by zero!");

35. Flow of Control
Each statement is executed in the order they are written
Flow control statements:
Conditional: if, if else, else, switch
Loop: for, while, do while
Escapes: break, continue, return

36. If, Else If, Else public double computeBodyMassIndex(){
if (this.height != 0){
IF-Statement }
else{
Else-Statement
public double computeBodyMassIndex(){
(this.height != 0) ? IF-Statement : Else-Statement; }

37. For Loop Person anahita = new Person("Anahita",24,0,90,'f');
Person arman = new Person("Arman",27,6,120,'m');
Person nazanin = new Person("Nazanin",26,6,85,'f');
Person[] family = {anahita,arman,nazanin};
for (int i=0;i<family.length;i++){
System.out.println(family[i].getName()); }
for (Person p:family){
System.out.println(p.getName()); }

38. While Loop Person anahita = new Person("Anahita",24,0,90,'f');
Person arman = new Person("Arman",27,6,120,'m');
Person nazanin = new Person("Nazanin",26,6,85,'f');
Person[] family = {anahita,arman,nazanin};
int i=0;
while(i<family.length){
System.out.println(family[i].getName());
i++; }

39. Break Causes an exit from the innermost while, for and switch
Person[] femaleFamily = family;
for (int i=0;i<family.length;i++){
// System.out.println(family[i].getName());
if (family[i].getGender() == 'm'){
System.out.println( family[i].getName() + " cannot be part of this list! :D");
break; }

40. Continue Can be used with while and for
Causes the innermost loop to start the next iteration
Person[] femaleFamily = family;
for (int i=0;i<family.length;i++){
if (family[i].getGender() == 'm'){
continue; }
System.out.println(family[i].getName());

41. Collections Iterable Most commonly used collection classes:
Arrays: fixed size
Lists (interface): length is not fixed -> add, remove functions
Sets (interface): contain unique items
Maps: a set of (key,value). key is unique.

42. Arrays A list of similar objects/primitives
Has fixed name, type, length
The elements are accessed by their index (starting from 0)
Person anahita = new Person("Anahita",24,0,90,'f');
Person arman = new Person("Arman",27,6,120,'m');
Person nazanin = new Person("Nazanin",26,6,85,'f');
Person[] family = {anahita,arman,nazanin};
Person[] family = new Person[3];
family[0] = anahita;
family[1] = arman;
family[2] = nazanin;

43. Exceptions
Handle situations in which your code doesn't work exactly as planned
Two types:
Checked exceptions: are checked by the compiler (meaning the compiler makes sure that they get handled somewhere in your code).
Unchecked exceptions (also called runtime exceptions): are not checked by the compiler.
Shlomo Hershkop

44. Try, Catch & Finally
public double computeBodyMassIndex() throws ArithmeticException{
if (this.height != 0){
double bmi = this.weight / Math.pow((double)this.height,2);
System.out.print(this.name + "'s " + "BMI is: " + bmi);
return bmi; }
else{
throw new ArithmeticException("Division by zero!");
try{
Double bmi = anahita.computeBodyMassIndex();
FileInputStream file = new FileInputStream("anahita.txt");
int output = file.read();
} catch(ArithmeticException e){
System.out.println(e.getMessage());
} catch (Exception e){
} finally{
System.out.println("Test is done."); }

45. What has not covered? I/O stream Filters Object serialization
Nested classes and anonymous classes
Regular expressions
Generics
Enum types
Reflection
JavaBeans …

46. Reserved Words abstract for switch assert goto synchronized boolean if
this
byte
implements
throw
break
import
throws
case
instanceof
transient
catch
int
try
char
interface
void
class
long
volatile
const
native
while
continue
new
default
package
false do
private
true
double
protected
null
else
public
enum
return
extends
short
final
static
finally
strictfp
float
super

47. References