SSE3052: Embedded Systems Practicecsl.skku.edu/uploads/SSE3052S18/6-Java.pdf · SSE3052: Embedded...

SSE3052: Embedded Systems Practice, Spring 2018, Jinkyu Jeong ([email protected])

SSE3052: Embedded Systems Practice

Minwoo Ahn

[email protected]

Computer Systems Laboratory

Sungkyunkwan University

http://csl.skku.edu

mailto:[email protected]

http://csl.skku.edu/

SSE3052: Embedded Systems Practice, Spring 2018, Jinkyu Jeong ([email protected]) 2

Agenda

• Learning Java!

– Installation

– Class, method, and object

– Inheritance

– Predefined class (String)

– Interface

– Exception handling

– ArrayList


Object oriented programming

https://kienthuc24h.com/wp-content/uploads/2017/07/class.jpg

▪ Color

▪ Type

▪ Fuel

▪ Company

Vehicle class

Inheritance


Installation

• JDK (Java Development Kit)– Check if JDK is installed (maybe not installed)

• $javac –version

– If not, install JDK

• $sudo apt install default-jdk

• Eclipse IDE

– Go to http://www.eclipse.org/downloads/

– Download “Eclipse IDE for Java Developers”

– Untar

– Execute “eclipse-inst”

http://www.eclipse.org/downloads/


Warm up (Hello World!)

public class HelloWorld {

public static void main(String[] args) {

System.out.println(“Hello World!”);

}

}

HelloWorld class

main method (~= function in C language)

public access modifier (public, private, protected)


C code vs. Java code

• C code

int funcA() {…}

int funcB() {…}

int funcC() {…}

int main() {

funcA();

funcB();

funcC();

}

• Java code

class classA {

int methodA() {…}

int methodB() {…}

int methodC() {…}

}

class classB {

int methodA() {…}

int methodB() {…}

int methodC() {…}

}

class classC {

static void main() {…}

}


Class

• A class is a template that describes data and behavior

• Similar with “structure” in C language

Ex)class person {

String firstName; // Instance variable

public String getFirstName() { //Getter (method)

return firstName;

}

public void setFirstName(String firstName) { // Setter (method)

this.firstName = firstName;

}

}


Constructor

class Person {

String firstName;

String lastName;

int age;

public void Person(String a, String b, int value) {

firstName = a;

lastName = b;

age = value;

}

public String getFirstName() {

return firstName;

}

public void setFirstName(String firstName) {

this.firstName = firstName;

}

public String getLastName() {

return lastName;

}

public void setLastName(String lastName) {

this.lastName = lastName;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public String toString() {

return firstName + " " + lastName;

}

}


Object

• An object is an instance of a class

Ex)

public class Main {


Person person = new Person(“Jim”, “Knopf”, 21);

Person p2 = new Person(“Jill”, “Sanders”, 20);

// Jill gets married to Jim

// and takes his name

p2.setLastName(“Knopf”);

System.out.println(p2); // “Jill Knopf” will printed

}

}


Constructor

• A special “method” that is invoked when creation of instance

• Name of constructor is ALWAYS the name of the class

• No return type

• One class can include several constructor (overloading)

• If no explicit constructor is defined, compiler implicitly adds a

constructor with default values


Example (3 constructors)class Person {

String firstName;

String lastName;

int age;

public Person() {

firstName = "No";

lastName = "Name";

age = 0;

}

public Person(String a, String b) {

firstName = a;

lastName = b;

age = 0;

}

public Person(String a, String b, int value) {

firstName = a;

lastName = b;

age = value;

}

…

}


Method overloading

• More than on method with the same name, different arguments

• Type of return value doesn’t matter

Ex)

Class PrintStream {

public void println(String s) {…}

public void println(double a) {…}

}

class PrintStream {

public void println(String s) {…}

public int println(String s) {…}

}

(O)

(X)


Exercise 1

• Implement a class circle that has methods double getArea() and

double getPerimeter(). In the constructor, supply the radius of the

circle. If radius is not given by user, default value is 10.


Inheritance

• A subclass which derived from superclass

Ex)

Class Person {

…

}

Class Students extends Person {

int grade;

public Student() {…}

}

Person

Student Doctor Professor

Superclass

Subclass


Example (Student derived from Person)class Student extends Person {

int grade;

public Student(String a, String b, int age, int grade) {

super(a, b, age); //Constructor of superclass Person

this.grade = grade;

}

public int getGrade() {

return grade;

}

public void setGrade(int grade) {

this.grade = grade;

}


return getFirstName() + " " + getLastName() + " is grade " + grade;

}

}


Example cont. (Main)

class Main {


Student s1 = new Student("Bill", "Gates", 13, 9);

s1.setFirstName("Steve");

s1.setGrade(10);

System.out.println(s1);

//”Steve Gates is grade 10” will printed

}

}


Method overriding

• Method redeclarationEx)

class BaseClass {


return “Base”;

}

}

class ChildClass extends BaseClass {


return “Child”;

}

}


Method overriding

public class Main {

public static void main(String[] args){

BaseClass a = new BaseClass();

ChildClass b = new ChildClass();

System.out.println(a); //”base”

System.out.println(b); //”child”

}

}


Available access modifier

Modifier Class Package Subclass World

public Y Y Y Y

protected Y Y Y N

No modifier Y Y N N

private Y N N N


String class

• String class represents array of characters

– All string literals are implemented as instances of String class

• Strings are immutable

• Initialization

– Ex) String s = “text”;

– Ex) String s = new String(“text”);


String methods• char charAt(int index)

– Returns the char value at the specified index.

• String concat(String str)

– Concatenates the specified string to be the end of this string.

• boolean endsWith(String suffix)

– Tests if this string ends with the specified suffix.

• boolean equals(Object anObject)

– Compares this string to the specified object.

• int indexOf(int ch)

– Returns the index within this string of the first occurrence of the specified character.

• int indexOf(String str)

– Returns the index within this string of the first occurrence of the specified substring.

• int length()

– Returns the length of this string.

• More APIs: https://docs.oracle.com/javase/8/docs/api/

https://docs.oracle.com/javase/8/docs/api/


Exercise 2

• Write a superclass Worker and subclasses HourlyWorker and SalariedWorker.

Every worker has a name and a salary rate. Write a method computePay(int

hours) that computes the weekly pay for every worker. An hourly worker

gets paid the hourly wage for the actual number of hours worked, if hours

is at most 40. If the hourly worker worked more than 40 hours, the excess

is paid at time and a half. The salaried worker gets paid the hourly wage for

40 hours, no matter what the actual number of hours is. Supply a test

program to test these classes and methods. (Provide toString() for each

classes)


Interface

• Declares a set of methods and their signatures

• Unlike class

– Provides no implementation

– Cannot instantiate

– Does not contain any constructor

Ex)

public interfaceWorker {

double computePay(int hours);

}


implement for interface

public class HourlyWorker implements Worker {

private double rate;

public HourlyWorker(double rate) {

this.rate = rate;

}

public double computePay(int hours) {

if (hours > 40)

return (hours – 40) * rate * 1.5 + 40 * rate;

else

return hours * rate;

}

}


implement for interface cont.

public class SalariedWorker implements Worker {

private int rate;

public SalariedWorker(int rate) {

this.rate = rate;

}

public double computePay(int hours) {

if (hours > 40)

return 40 * rate;

else

return hours * rate;

}

}



public class Main {


Worker worker1 = new Worker(); // Error

Worker worker2 = new HourlyWorker(7.5);

Worker worker3 = new SalariedWorker(10);

System.out.println("worker2: " + worker2.computePay(40));

System.out.println("worker3: " + worker3.computePay(80));

}

}



public class SomeClass {

public void howMuch(Worker worker) {

System.out.println("You earn " + worker2.computePay(40));

}

}

// “You earn 300” will printed for worker2

// “You earn 400” will printed for worker3


Implementing multiple interfaces

• A class can implement multiple interfaces– Cannot inherit multiple superclasses

Ex)

public interface AAA {

public int a();

}

public interface BBB {

public int b();

}

public class CCC implements AAA,BBB {

public int a() {…};

public int b() {…};

}


Exception handling

• An exception is an event to indicate an error

Throw

Catch


Types of exceptions

• Checked exception

– Checked at compile-time

– All subclasses of Exception except RuntimeException

• Unchecked Exception

– Not checked at compile-time rather checked at runtime

– Subclasses of RuntimeException

Ex) ArithmeticException

Int a = 50 / 0;

Ex) NullPotinerException

String s = null;

System.out.println(s.length);

Ex) ArrayIndexOutofBoundsException

Int a[] = new int [5];

a[10] = 50;


Throwing exception

public class BankAccount {

public void withdraw(double amount) {

if (amount > balance) {

//

// now what?

}

balance = balance – amount;

}

}


Throwing exception cont.

public class BankAccount {

public void withdraw(double amount) {

if (amount > balance) {

IllegalArgumentException exception = new IllegalArgum

entException("Amount exceeds balance");

throw exception;

}

balance = balance – amount;

}

}


Catching exception


BankAccount acct = new BankAccount(100);

try {

acct.withdraw(200);

} catch (IllegalArgumentException ex) {

System.out.println("Withdraw failed.");

//or ex.printStackTrace();

}

}


Exercise 3

• Modify the BankAccount class to throw IllegalArgumentException

when the account is constructed with a negative balance, when a

negative amount is deposited, or when an amount that is not

between 0 and the current balance is withdrawn. Write a test

program that causes all three exceptions to occur and that

catches them all


ArrayList

• An ArrayList is a sequence of objects

Ex) Assume that Coin class is already defined

ArrayList coins = new ArrayList();

coins.add(new Coin(0.1,“dime”));

coins.add(new Coin(0.25, “quarter”));


ArrayList methods

• boolean add(E e)

– Appends the specified element to the end of this list.

• void add(int index, E element)

– Inserts the specified element at the specified position in this list.

• E get(int index)

– Returns the element at the specified position in this list.

• E remove(int index)

– Removes the element at the specified position in this list.

• int size()

– Returns the number of elements in this list.


Exercise 4

• Implement a class Bank that contains an array list of BankAccount

objects. Support methods,

– public void addAccount(double initialBalance)

– public void deposit(int account, double amount)

– public void withdraw(int account, double amount)

– public double getBalance(int account)

• An account number is simply an index into the array list

SSE3052: Embedded Systems Practicecsl.skku.edu/uploads/SSE3052S18/6-Java.pdf · SSE3052: Embedded...

Documents

Transcript of SSE3052: Embedded Systems Practicecsl.skku.edu/uploads/SSE3052S18/6-Java.pdf · SSE3052: Embedded...