HelloWorld
public class HelloWorldApp {
public static void main(String[] args) {
System.out.println("Hello World!!");
}
}Datatype
public class Datatype{
public static void main(String[] args) {
System.out.println(6);//Number
System.out.println("six");//string
System.out.println("6");//string 6
System.out.println(6+6); // 12
System.out.println("6"+"6"); // 66
System.out.println(6*6); // 36
// System.out.println("6"*"6");
System.out.println("1111".length()); // 4
// System.out.println(1111.length());
System.out.println("Hello World"); //String 문자열
System.out.println('H'); //Char 문자
System.out.println("H");
}
}
Number
public class Number {
public static void main(String[] args) {
System.out.println(6 + 2); //8
System.out.println(6-2);//4
System.out.println(6*2);//12
System.out.println(6/2);//3
System.out.println(Math.PI); //3.14
System.out.println(Math.floor(Math.PI));//내림
System.out.println(Math.ceil(Math.PI));//올림
}
}String
public class StringApp {
public static void main(String[] args) {
// Character VS String
System.out.println("Hello World"); // String
System.out.println('H'); // Character
System.out.println("H");
System.out.println("Hello "
+ "World");
// new line
System.out.println("Hello \nWorld");
// escape
System.out.println("Hello \"World\"");// Hello "World"
}
}
변수
public class variable {
public static void main(String[] args) {
int a = 1; // Number -> integer
System.out.println(a);
double b = 1.1; // real number -> double
System.out.println(b);
String c = "Hello World";
System.out.println(c);
}
}public class Letter {
public static void main(String[] args) {
String name = "eunryong";
System.out.println("Hello, "+name+" ..."+name+" bye"); //대입
double VAT = 10.0;
System.out.println(VAT);
}
}casting
public class Casting {
public static void main(String[] args) {
double a = 1.1;
double b = 1;
double b2 = (double)1;
System.out.println(b);
// int c = 1.0;
double d = 1.1;
int e = (int)1.1;
System.out.println(e);
String f = Integer.toString(1);
System.out.println(f.getClass());//getClass:check datatype
}
}IOT 라이브러리 이용
import org.opentutorials.iot.Elevator;
import org.opentutorials.iot.Lighting;
import org.opentutorials.iot.Security;
public class OkJavaGoInHome {
public static void main(String[] args) {
String id = "JAVA APT 507";
// Elevator call
Elevator myElevator = new Elevator(id);
myElevator.callForUp(1);
// Security off
Security mySecurity = new Security(id);
mySecurity.off();
// Light on
Lighting hallLamp = new Lighting(id+" / Hall Lamp");
hallLamp.on();
Lighting floorLamp = new Lighting(id+" / floor Lamp");
floorLamp.on();
}
}
디버거
breakpoint, perspective(debug) 이용
resume : 다음 breakpoint 가 나올 때까지 한번에 실행
terminate : 코딩하던 화면으로 돌아옴 (디버깅 끝)
step into : 해당 열의 method가 어떻게 구성되어 있는지 확인 할 수 있음
step over : 한 열씩 실행
step return : 디버거 수행장면으로 돌아옴
입력
String id = JOptionPane.showInputDialog("Enter a ID");
String Bright = JOptionPane.showInputDialog("Enter a Bright level");method
// refactor Extract method
public class WhyMethod {
public static void main(String[] args) {
printTwoTimesA();
printTwoTimesA();
printTwoTimesA();
}
public static void printTwoTimesA() {
System.out.println("-");
System.out.println("a");
System.out.println("a");
}
}method 입력
public class WhyMethod {
//인자, argument
public static void main(String[] args) {
printTwoTimesA("a", "-");
printTwoTimesA("a", "*");
printTwoTimesA("b", "^");
printTwoTimesA("b", "!");
}
//매개변수,parameter
public static void printTwoTimesA(String text, String delimiter) {
System.out.println(delimiter);
System.out.println(text);
System.out.println(text);
}
}public: 공용
private: 같은 클래스 안의 메소드만 이용 가능
static: class method
non-static: instance method
