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Introduction toJava Programming

Y. Daniel LiangEdited by Hoàng Văn Hậu – VTC Academy – THSoft co.,ltd

https://play.google.com/store/apps/developer?id=THSoft+Co.,Ltd

VTC Academy THSoft Co.,Ltd 2

Introduction

Course Objectives Organization of the Book


Course Objectives Upon completing the course, you will understand

– Create, compile, and run Java programs

– Primitive data types

– Java control flow

– Methods– Arrays (for teaching Java in two semesters, this could be the end)

– Object-oriented programming

– Core Java classes (Swing, exception, internationalization, multithreading, multimedia, I/O, networking, Java Collections Framework)


Course Objectives, cont.

You will be able to – Develop programs using Eclipse IDE– Write simple programs using primitive data

types, control statements, methods, and arrays.– Create and use methods– Write interesting projects


Session 03: Method and Class

Methods Object-Oriented Programming Classes Packages Subclassing and Inheritance Polymorphism


Introducing Methods

Method StructureA method is a collection of statements that are grouped together to perform an operation.


Introducing Methods, cont.•parameter profile refers to the type, order, and number of the parameters of a method.

•method signature is the combination of the method name and the parameter profiles.

•The parameters defined in the method header are known as formal parameters.

•When a method is invoked, its formal parameters are replaced by variables or data, which are referred to as actual parameters.


Declaring Methods

public static int max(int num1, int num2) {

if (num1 > num2) return num1; else return num2;}


Calling Methods, cont.

public static void main(String[] args) { int i = 5; int j = 2; int k = max(i, j); System.out.println( "The maximum between " + i + " and " + j + " is " + k); }

public static int max(int num1, int num2) { int result; if (num1 > num2) result = num1; else result = num2; return result; }

pass i pass j


Calling Methods, cont.

The main method i: j: k:

The max method num1: num2: result:

pass 5

5

2

5

5

2

5

pass 2 parameters


CAUTION

A return statement is required for a nonvoid method. The following method is logically correct, but it has a compilation error, because the Java compiler thinks it possible that this method does not return any value. public static int xMethod(int n) { if (n > 0) return 1; else if (n == 0) return 0; else if (n < 0) return –1; }

To fix this problem, delete if (n<0) in the code.


Actions on Eclipse

Open Eclipse IDE– Create project: Session3Ex– Create package: com.vtcacademy.exopp– Create java class: Ex3WithOpp.java (with main method)– Create java class: Circle.java

RunRunSourceSource


The Math Class Class constants:

– PI– E

Class methods: – Trigonometric Methods – Exponent Methods– Rounding Methods– min, max, abs, and random Methods


Trigonometric Methods

sin(double a)

cos(double a)

tan(double a)

acos(double a)

asin(double a)

atan(double a)


Exponent Methods exp(double a)

Returns e raised to the power of a.

log(double a)

Returns the natural logarithm of a.

pow(double a, double b)

Returns a raised to the power of b.

sqrt(double a)

Returns the square root of a.


Rounding Methods double ceil(double x)

x rounded up to its nearest integer. This integer is returned as a double value.

double floor(double x)x is rounded down to its nearest integer. This integer is returned as a double value.

double rint(double x)x is rounded to its nearest integer. If x is equally close to two integers, the even one is returned as a double.

int round(float x)Return (int)Math.floor(x+0.5).

long round(double x)Return (long)Math.floor(x+0.5).


min, max, abs, and random

max(a, b)and min(a, b)Returns the maximum or minimum of two parameters.

abs(a)Returns the absolute value of the parameter.

random()Returns a random double valuein the range [0.0, 1.0).


Example 3.1 Computing Mean and Standard Deviation

Generate n random numbers and compute the mean and standard deviation

n

xmean

n

ii

1

1

)(

1

2

12

nn

xx

deviation

n

i

n

ii

i


Example 3.2 Obtaining Random Characters

Write the methods for generating random characters. The program uses these methods to generate 175 random characters between ‘!' and ‘~' and displays 25 characters per line. To find out the characters between ‘!' and ‘~', see Appendix B, “The ASCII Character Set.”


OO Programming Concepts

data field 1

method n

data field n

method 1

An object

...

...

State

Behavior

Data Field radius = 5

Method findArea

A Circle object


Class and Objects

circle1: Circle

radius = 2

new Circle()

circlen: Circle

radius = 5

new Circle()

...

UML Graphical notation for classes

UML Graphical notation for objects

Circle

radius: double

findArea(): double

UML Graphical notation for fields

UML Graphical notation for methods

Illustration on code


Class Declaration

class Circle { double radius = 1.0;

double findArea(){ return radius * radius * 3.14159; }}


Declaring Object Reference Variables

ClassName objectReference;

Example:Circle myCircle;


Creating Objects

objectReference = new ClassName();

Example:myCircle = new Circle();

The object reference is assigned to the object reference variable.


Declaring/Creating Objectsin a Single Step

ClassName objectReference = new ClassName();

Example:Circle myCircle = new Circle();Circle myCircle2;


Constructors

Circle(double r) { radius = r;}

Circle() { radius = 1.0; }

myCircle = new Circle(5.0);

Constructors are a special kind of methods that are invoked to construct objects.


Constructors, cont.A constructor with no parameters is referred to as a default constructor.

Constructors must have the same name as the class itself.

Constructors do not have a return type—not even void.

Constructors are invoked using the new operator when an object is created. Constructors play the role of initializing objects.


Example 3.3 Using Classes from the Java Library

Objective: Demonstrate using classes from the Java library. Use the JFrame class in the javax.swing package to create two frames; use the methods in the JFrame class to set the title, size and location of the frames and to display the frames.



Subclassing and Inheritance

private None protected Public



Example 3.4

Shape

TwoDimensionalShape ThreeDimensionalShape

Circle Square Triangle Sphere Cube Tetrahedron


Example 3.4

http://blogs.unsw.edu.au/comp1400/blog/2011/09/tut-10/


Abstract Classes and Methods

Abstract classes – Are superclasses (called abstract superclasses)– Cannot be instantiated – Incomplete

subclasses fill in "missing pieces"

Concrete classes– Can be instantiated– Implement every method they declare– Provide specifics


Abstract Classes and Methods (Cont.)

Abstract classes not required, but reduce client code dependencies

To make a class abstract– Declare with keyword abstract– Contain one or more abstract methods

public abstract void draw();

– Abstract methods No implementation, must be overridden


Abstract Classes and Methods (Cont.)

Application example– Abstract class Shape

Declares draw as abstract method

– Circle, Triangle, Rectangle extends Shape Each must implement draw

– Each object can draw itself

Iterators– Array, ArrayList (Chapter 22)

– Walk through list elements

– Used in polymorphic programming to traverse a collection



Case Study: Creating and Using Interfaces

Use interface Shape– Replace abstract class Shape

Interface– Declaration begins with interface keyword

– Classes implement an interface (and its methods)

– Contains public abstract methods Classes (that implement the interface) must implement

these methods


1 // Fig. 10.18: Shape.java

2 // Shape interface declaration.

3

4 public interface Shape {

5 public double getArea(); // calculate area

6 public double getVolume(); // calculate volume

7 public String getName(); // return shape name

8

9 } // end interface Shape

Lines 5-7Classes that implement Shape must implement these methods


1 // Fig. 10.19: Point.java

2 // Point class declaration implements interface Shape.

3

4 public class Point extends Object implements Shape {

5 private int x; // x part of coordinate pair

6 private int y; // y part of coordinate pair

7

8 // no-argument constructor; x and y default to 0

9 public Point()

10 {

11 // implicit call to Object constructor occurs here

12 }

13

14 // constructor

15 public Point( int xValue, int yValue )

16 {

17 // implicit call to Object constructor occurs here

18 x = xValue; // no need for validation

19 y = yValue; // no need for validation

20 }

21

22 // set x in coordinate pair

23 public void setX( int xValue )

24 {

25 x = xValue; // no need for validation

26 }

27

Error compile


Action on class

Teacher – [email protected]– 0984380003– https://play.google.com/store/search?q=thsoft+co&c=apps

Captions Members

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Technology

int num2

return num2

num1 num2 result

bookvtc academy thsoft

main method

method signature

method headerare

following method