클래스 이해하기

1. 클래스 이해하기

2. 클래스 작성 방법 • 클래스 작성 class class_name{ public int Varname; //멤버변수 public voint Print(){ } //메소드 } • class 선언하기 • class_namename = newclass_name(); • 멤버 변수, 메소드 사용하기 • name.Varname=10 • name.Print(); 컴퓨터과학과 비젼랩

3. //클래스 작성 방법 class MemberVar{ public static void main(String args[]){ data1objectVar = new data1(); objectVar.intVar = 10; objectVar.strVar = “kim”; System.out.println(objectVar.intVar); } } class data1{ int intVar; String strVar; } 컴퓨터과학과 비젼랩

4. 객체 생성 • data1objectVar = new data1(); class data1 objectVar int intVar; String strVar; int intVar; String strVar; new 연산자는 객체를 복사 컴퓨터과학과 비젼랩

5. 객체 생성자란? • 생성자 • 클래스 이름이 같은 함수 • data1 objectVar = new data1(); • 역할 • 멤버 변수의 초기화, 객체 생성 • 생성자가 없는 클래스는 내부적으로 생성 class data1{ int intVar; String strVar; data1(){ }// 내부적으로 생성 } 컴퓨터과학과 비젼랩

6. //생성자 함수를 사용하지 않는 형태 class Salary{ String name; double amount; } class Payroll{ public static void main(String args[]){ Salary sal = new Salary(); sal.name=“kim young soo”; sal.amount=1000000.0; System.out.print(sal.name+“:”+sal.amount); } }

7. //생성자 class Salary{ String name; double amount; Salary() { } } class Payroll{ public static void main(String args[]){ Salary sal = new Salary(); sal.name=“kim young soo”; sal.amount=1000000.0; System.out.print(sal.name+“:”+sal.amount); } }

8. //생성자 함수 활용 class Salary{ String name; double amount; Salary(String n, double a) { name = n; amount = a; } } class Payroll{ public static void main(String args[]){ Salary sal = new Salary(“park js”,100000.0); System.out.print(sal.name+“:”+sal.amount); } }

9. //함수 or 생성자 구분 class Salary{ String name; double amount; voidSalary(String n, double a) { name = n; amount = a; } } class Payroll{ public static void main(String args[]){ Salary sal = new Salary(“kim yw”,100000.0); System.out.print(sal.name+“:”+sal.amount); } }

10. 생성자 오버로딩

11. class Salary{ //생성자 오버로딩 String name; double amount; Salary(){ } Salary(String n, double a) { name = n; amount = a; } void setName(String name){ this.name = name; } } class Payroll{ public static void main(String args[]){ Salary salOne = new Salary(); salOne.setName(“kim young won”); System.out.print(salOne.name+“:”+salOne.amount); } }

12. 메소드 오버로딩

13. class OverloadDemo{ void test(){ System.out.println(“No parameters”); } void test(int a, int b){ System.out.println(“a and b:”+a+ “ ”+b);} double test(double a){ System.out.println(“double a:”+a); return a*a; } } class Overload{ public static void main(String[] args){ OverloadDemo ob = new OverloadDemo(); double result; ob.test(); ob.test(10); ob.test(10,20); result = ob.test(123.2); System.out.println(“Result of ob.test(123.2):”+result); } }

14. class Salary{ //메소드 오버로딩 String name; double amount; Salary(String n, double a) { name = n; amount = a; } void raiseSalary(double byPercent){amount*=1+byPercent/100;} void raiseSalary(double byPercent, double bonus){ amount+= amount*byPercent/100+amount*bonus/100; } } class Payroll{ public static void main(String args[]){ Salary salOne = new Salary(“ywkim”,1000000.0); salOne.raiseSalary(5,4); System.out.print(salOne.name+“:”+salOne.amount); } }

15. 참조값 바꾸기 • call-by-value • call-by-reference 컴퓨터과학과 비젼랩

16. //call-by-value class CallTest{ publicstaticvoid main(String[] argv){ int num1=10, num2=20; System.out.println("num="+num1+ "num2="+num2); new CallTest().swap(num1,num2); System.out.println("num="+num1+ "num2="+num2); } void swap(int a,int b){ int temp; temp = a; a = b; b = temp; } }

17. class CallTest{ publicstaticvoid main(String[] argv){ Int num1 = new Int(10), num2 = new Int(20); System.out.println("num="+num1+ "num2="+num2); new CallTest().swap(num1,num2); System.out.println("num="+num1+ "num2="+num2); } void swap(Int a,Int b){ Int temp; temp = a; a = b; b = temp; System.out.println(a.vlaue + “ “ + b.value); } } class Int{ int value; Int(int value) { this.value = value; } public String toString(){ return Integer.toString(value); } }

18. class CallTest{// call-by-reference publicstaticvoid main(String[] argv){ Int num1 = new Int(10), num2 = new Int(20); System.out.println("num="+num1+ "num2="+num2); new CallTest().swap(num1,num2); System.out.println("num="+num1+ "num2="+num2); } void swap(Int a,Int b){ int temp; temp = a.value; a.value = b.value; b.value = temp; } } class Int{ int value; Int(int value) { this.value = value; } public String toString(){ return Integer.toString(value); } }

19. 멤버 변수의 상속

20. class SchoolMember{ private String name = “kim young won"; } class Student extends SchoolMember{ public long studentnumber = 200100001; } class StudentManager{ publicstaticvoid main(String args[]){ Student st = new Student(); System.out.println(st.name); System.out.println(st.studentnumber); } }

21. 상속

22. class A{ int i; int j; void setij(int x,int y){ i = x; j = y;} } class B extends A{ int total; void sum(){ total = i +j; } } class Access{ publicstaticvoid main(String args[]){ B subOb = new B(); subOb.setij(10,20); subOb.sum(); System.out.println("총합은" + subOb.total); } }

23. 수퍼(super) 클래스의 private 멤버접근

24. class SchoolMember{ private String name = “kim y w"; String getName(){ return name;} } class Student extends SchoolMember{ public long studentnumber = 20010001; } class StudentManager{ publicstaticvoid main(String args[]){ Student st = new Student(); System.out.println(st.getName()); } }

25. 오버라이딩

26. class SchoolMember{ String name; publicvoid register(String na){ name = na; } } class Student extends SchoolMember{ publicvoid register(String na){ name = na + "Sir"; } } class StuMgn{ publicstaticvoid main(String args[]){ Student stu1 = new Student(); stu1.register("kim"); System.out.println(stu1.name); SchoolMember stu2 = new Student(); stu2.register("kim"); System.out.println(stu2.name); } }

27. class A{ int i,j; A(int a, int b) { i = a; j = b;} void show(){ System.out.println(“i와 j”+ i+j);} } class B extends A{ int k; B(int a,int b,intc){ super(a,b); k = c; } void show(){ System.out.println(“k는”+k);} } class Ovrride{ public static void main(String args[]){ B subOb = new B(1,2,3); subOb.show(); } }

28. class A{ int i,j; A(int a, int b) { i = a; j = b;} void show(){ System.out.println(“i와 j”+ i+j);} } class B extends A{ int k; B(int a,int b,int c){ super(a,b); k = c; } void show(String msg){ System.out.println(msg + k);} } class Ovrride{ public static void main(String args[]){ B subOb = new B(1,2,3); subOb.show(“k는”); subOb.show(); } }

29. 추상 클래스

30. abstract class Figure{ //추상 클래스 정의 double dim1; double dim2; Figure(double a, double b){dim1 = a; dim2 = b;} abstract double area(); } class Rectangle extends Figure{ Rectangle(double a, double b){ super(a,b);} double area(){ System.out.println(“사각형 내부”); return dim1*dim2; } } class Triangle extends Figure{ Triangle(double a, double b){super(a,b);} double area(){ System.out.println(“삼각형 내부”); return dim1*dim2/2; } }

31. class AbstractAreas{ // 추상화클래스 public static void main(String args[]){ Rectangle r = new Rectangle(9,5); Triangle t = new Triangle(10,8); Figure figref; figref = r; System.out.println(“사각형 면적은”+figref.area()); figref = t; System.out.println(“삼각형 면적은”+figref.area()); } }

32. 인터페이스

33. interface Callback{ //인터페이스 정의 void callback(int param); } class Client implements Callback{ public void callback(int p){ System.out.println(“callback called with”+p); } void nonIfacemethod(){ System.out.println(“Classes that implement interface”+”may also define other mebers, too.”); } } class AnotherClient implements callback{ public void callback(int p){ System.out.println(“Another version of callback”); System.out.println(“p squaed is”+(p*p)); } }

34. class TestIface{ //인터페이스 호출 public static void main(String args[]){ Callback c = new Client(); AnotherClient ob = new AnotherClient(); c.callback(10); c = ob; c.callback(10); } }

35. interface A{ //인터페이스 메소드는 모두 재정의 void meth1(); } interface B extends A{ void meth2(); void meth3(); } class Myclass implements A, B{ publci void meth1(){ System.out.println(“Implement meth1());} publci void meth2(){ System.out.println(“Implement meth2());} publci void meth3(){ System.out.println(“Implement meth3());} public static void main(Strin[] args){ Myclass m = Myclass(); m.meth1(); m.meth2(); m.meth3(); } }

36. 동일 클래스내의 변수 접근& 스테틱(static) 변수 접근

37. class StaticDemo{ staticint a = 20; staticint b = 30; staticvoid callme(){ System.out.println("a="+a); } } class StaticByName{ publicstaticvoid main(String[] args){ StaticDemo.callme(); System.out.println("b="+StaticDemo.b); } }

38. 밑줄 친 a변수에는 몇이 들어갈까요? class StaticShare{ static int a=0; void inc(){ a = a +2;} } class TestStatic{ public static void main(String[] args){ StaticShare s1 = new StaticShare(); StaticShare s2 = new StaticShare(); StaticShare s3 = new StaticShare(); s1.inc(); s2.inc(); s3.inc(); System.out.println(StaticShare.a); } } 컴퓨터과학과 비젼랩

39. Integer Class • 메소드 : static int parseInt(String s) import java.lang.*; publicclass Integertest{ publicstaticvoid main(String[] args){ int i,sum=0; for(i = 0 ; i < args.length ; i++){ sum += Integer.parseInt(args[i]); } System.out.println(sum); } } 컴퓨터과학과 비젼랩

40. Integer Class • double doubleValue() : Returns the value of this Integer as a double. • float floatValue() : Returns the value of this Integer as a float. • static Integer getInteger(String nm) • int intValue() : Returns the value of this Integer as an int. • long longValue() : Returns the value of this Integer as a long. • static int parseInt(String s) : Parses the string argument as a signed decimal integer. • short shortValue() : Returns the value of this Integer as a short. • String toString() : Returns a String object representing this Integer's value. 컴퓨터과학과 비젼랩

41. 한 문자씩 읽어오기 import java.io.*; public class ReadUsage{ public static void main(String args[]) throws IOException{ char c; System.out.println(“please input…, ‘q’ to quit.”); do{ c = (char) System.in.read(); System.out.print( c ); }while(c != ‘q’); } } 컴퓨터과학과 비젼랩

42. InputStream Class • 키보드로 부터 입력 • abstractint read(): Reads the next byte of data from the input stream. • Buffer에 저장된 내용을 입력 • int read(byte[] b): • Reads some number of bytes from the input stream and stores them into the buffer array b. • int read(byte[] b, int off, int len): • Reads up to len bytes of data from the input stream into an array of bytes 컴퓨터과학과 비젼랩

43. OutputStream Class • 콘솔에 출력 • abstractvoid write(int b): Writes the specified byte to this output stream. • OutputStream class의 인스턴스에 출력 • void write(byte[] b): • Writes b.length bytes from the specified byte array to this output stream. • void write(byte[] b, int off, int len): • Writes len bytes from the specified byte array starting at offset off to this output stream. • void close(): • Closes this output stream and releases any system resources associated with this stream. • Wirte()함수 호출 한 다음 반드시 호출 컴퓨터과학과 비젼랩