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Appendix A. JAVA Primer Basics Exception Handling Inheritance Interface and Abstract Classes

Appendix A. JAVA Primer Basics Exception Handling Inheritance Interface and Abstract Classes Applications and Applets. Basics. A Simple Program /* * 첫 번째의 간단한 프로그램 * / Public class First { public static void main(String args[]) { // 메시지를 스크린에 출력한다 .

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Appendix A. JAVA Primer Basics Exception Handling Inheritance Interface and Abstract Classes

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  1. Appendix A. JAVA Primer • Basics • Exception Handling • Inheritance • Interface and Abstract Classes • Applications and Applets

  2. Basics • A Simple Program /* * 첫 번째의 간단한 프로그램 */ Public class First { public static void main(String args[]) { // 메시지를 스크린에 출력한다. System.out.println(“Java Primer Now Brewing!”); } } • Compilation & Execution – Java Development Kit (JDK) • Javac First.java -> First.class • Java First

  3. Basics • Methods Public class Second { public static void printIt(String message) { System.out.println(message); } public static void main(String args[]) { printIt(“Java Primer Now Brewing!”); } } • Operators • Arithmetic: + - * / & ++ -- += • Logical: && || • Relational: == != < <= >= > • No Operator Overloading • Exception: System.out.println(“Can you hear ” + “me?”);

  4. Basics – Statements • for for(initialization; test; increment) { // loop body } int i; for(i = 1; i <= 25; i++) { System.out.println(“i = ” + i); } • while while(Boolean condition is true) { // loop body } do { // loop body } while(Boolean condition is true);

  5. Basics – Data Types • if if(Boolean condition is true) { // 문장(들) } else if(Boolean condition is true) { // 다른 문장(들) } else { // 또 다른 문장(들) } • Data Types • 기본형 – boolean, char, byte, short, int, long, float, double • 참조형 – 객체 및 배열

  6. Basics – Classes & Objects (1/4) • Point Class class Point { // 객체를 초기화하기 위한 생성자 public Point(int i, int j) { xCoord = i; yCoord = j; } // xCoord와 yCoord의 값을 교환한다. public void swap() { int tmp; tmp = xCoord; xCoord = yCoord; yCoord = tmp; } public void printIt() { System.out.println(“X coordinate = “ + xCoord); System.out.println(“Y coordinate = “ + yCoord); } // 클래스 데이터 private int xCoord, yCoord; // X & Y 좌표 }

  7. Basics – Classes & Objects (2/4) • Object Instantiation Point ptA = new Point(0, 15); • Undefined Constructor Point ptA = new Point(); • Method Overloading public Point() { xCoord = 0; yCoord = 0; } • Method Calls – object-name.method ptA.swap(); ptA.printIt(); • Protection private, public, protected • Constants public static final double PI = 3.14159;

  8. Basics – Classes & Objects (3/4) • Reference public class Third { public static void main(String args[]) { // 두 개의 점을 생성하여 초기화한다. Point ptA = new Point(5,10); Point ptB = new Point(-15, -25); // 그들의 값을 출력한다. ptA.printIt(); printB.printIt(); // 이제 첫 번째 점의 값들을 교환한다. ptA.swap(); ptA.printIt(); // ptC는 ptB에 대한 참조이다. Point ptC = ptB; // ptC의 값들을 교환한다. ptC.swap(); // 값을 출력한다. ptB.printIt(); ptC.printIt(); } } xCoord = 5 yCoord = 10 ptA xCoord = -15 yCoord = -25 ptB ptC

  9. Basics – Classes & Objects (4/4) • Parameter Passing – Call by Reference public static void chage(Point tmp) { tmp.swap(); } Point ptD = new Point(0, 1); change(ptD); ptD.printIt();

  10. Basics – Arrays • Array of 10 bytes bype[] numbers = new byte[10]; • Initialization int[] primeNums = {3, 5, 7, 11, 13}; • Array of Objects Point[] pts = new Point[5]; for(int i = 0; i < 5; i++) { pts[i] = new Point(i, i); pts[i].printIt(); }

  11. Basics – Packages • Usage java.<package name>.<class.name> • Examples java.lang.String java.lang.Thread java.util.Vector items = new java.util.Vector(); import java.util.Vector; Vector items = new Vector(); import java.util.*; http://www.javasoft.com

  12. Exception Handling public final void wait() throws InterruptedException; try { // 예외를 유발할 수 있는 어떤 method를 부른다. } catch(theException e) { // 이제 예외를 처리한다. } finally { // 예외가 발생하든 않든 간에 이를 수행한다. }

  13. Exception Handling – Examples public class TestExcept { public static void main(String args[]) { int num, recip; // 무작위수 0 또는 1을 생성한다. num = (int) (Math.random() * 2); try { recip = 1 / num; System.out.println(“The reciprocal is “ + recip); } catch (ArithmeticException e) { // 예외 메시지를 출력한다. System.out.println(e); } finally { System.out.println(“The number was “ + num); } } } int[] num = {5, 10, 15, 20, 25}; for(int i = 0; I < 6; i++) System.out.println(num[i]);

  14. public class Person { public Person(String n, Strings) { name = n; age = a; ssn = s; } public void printPerson() { System.out.println( “Name: “ + name); System.out.println( “Age: “ + age); System.out.println( “Sociral Security: “ + ssn); } private String name; private int age; private String ssn; } public class Student extends Person { public Student(String n, int a, String s, String m, double g){ // 부모 (Person) 클래스 내의 // 생성자 (constructor)를 호출한다. super(n, a, s); major = m; GPA = g; } public void studentInfo() { // 부모 클래스 내의 인쇄 method를 // 호출한다. printPerson(); System.out.println( “Major: “ + major); System.out.println(“GPA: “ + GPA); } private String major; private double GPA; } Inheritance

  15. Inheritance – java.util.Vector addElement(Object obj); String first = “The first Element”; String second = “The second element”; String third = “The third element”; Vector item = new Vector(); items.addElement(first); items.addElement(second); items.addElement(thrid); String element; element = (String) items.elementAt(0); System.out.println(element); element = (String) items.elementAt(1); System.out.println(element); element = (String) items.elementAt(2); System.out.println(element);

  16. Interface (1/3) • 객체 동작의 구현을 명세하지 않고도 객체 동작을 정의할 수 있다. public interface Shape { public double area(); public double circumference(); public static final double PI = 3.14159; }

  17. public class Circle implements Shape { // 원의 반경을 초기화한다. public Circle(double r) { radius = r; } // 원의 면적을 계산한다. public double area() { return PI * radius * radius; } // 원의 둘레를 계산한다. public double circumference() { return 2 * PI * radius; } private double radius; } public class Rectangle implements Shape { public Rectangle(double h, double w) { height = h; width = w; } // 사각형의 면적을 계산한다. public double area() { return height * width; } // 사각형의 둘레를 계산한다. public double circumference() { return 2 * (height + width); } private double height; private double width; } Interface (2/3)

  18. Interface (3/3) public class TestShapes { public static void display(Shape figure) { System.out.println(“The area is “ + figure.area()); System.out.println(“The circumference is “ + figure.circumference()); } public static void main(String args[]) { Shape figOne = new Circle(3.5); display(figOne); figOne = new Rectangle(3, 4); display(figOne); } }

  19. Abstract Classes (1/3) public abstract class Employee { public Empolyee(String n, String t, double s) { name = n; title = t; salary = s; } public void printInfo() { System.out.println(“Name: “ + name); System.out.println(“Title: “ + title); System.out.println(“Salary: $” + salary); } public abstract void computeRaise(); private String name; private String title; protected double salary; }

  20. public class Manager extends Employee { public Manager(String n, String t, double s) { super(n, t, s); } public void computeRaise() { salary += salary * .05 + BONUS; } private static final double BONUS = 2500; } public class Developer extends Employee { public Developer(String n, String t, double s, int np) { super(n, t, s); numOfPrograms = np; } public void computeRaise() { salary += salary * .05 + numOfPrograms * 25; } private int numOfPrograms; } Abstract Classes (2/3)

  21. Abstract Classes (3/3) Employee[] worker = new Employee[3]; worker[0] = new Manager(“Pat”, “Supervisor”, 30000); worker[1] = new Developer(“Tom”, “Java Tech”, 28000, 20); worker[2] = new Developer(“Jay”, “Java Intern”, 2600, 8); for(int i = 0; i < 3; i++) { worker[i].computeRaise(); worker[i].printInfo(); }

  22. import java.applet.*; import java.awt.*; public class FirstApplet extends Applet { public void init() { // 초기화 코드 } public void paint(Graphics g) { g.drawString( “Java Primer Now Brewing!”, 15, 15); } } <applet code = FirstApplet.class width = 400 height = 200> </applet> appletviewer FirstApplet.html Applications & Applets

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