240621 9주차 금요일 - JAVA 20

https://www.oracle.com/java/technologies/downloads/#jre8-windows

https://github.com/spring-attic/toolsuite-distribution/wiki/Spring-Tool-Suite-3

7zip다운

https://tomcat.apache.org/download-10.cgi

STS.ini열어서 맨윗줄에

-vm
C:\sts-bundle\common\jre1.8.0_411\bin\javaw.exe

맨밑줄에

-Dfile.encoding=UTF-8

 

추가

https://www.erdcloud.com/d/s5cxMny22Qe7Cze2r

=======================

 

자바 Instanceof 연산자

객체가 어떤 클래스인지, 어떤 클래스를 상속받았는지 확인하는데 사용하는 연산자

 

public static void main(String[] args) {
  A a = new A();
  B b = new B();

  System.out.println(a instanceof A);   // true 출력
  System.out.println(b instanceof A);   // true 출력 : A를 상속 받았기 때문
  System.out.println(a instanceof B);    // false 출력
  System.out.println(b instanceof B);    // true 출력
}

=======================================================

예외처리

int [] arr= {1,2,3,4,5};
int index=-1;
java.util.Scanner sc=new java.util.Scanner(System.in);

try {
System.out.println("출력하고싶은 배열 인덱스 입력");
index=Integer.parseInt(sc.nextLine());
System.out.println("사용자 배열내용은 : "+arr[index]);
}catch(ArrayIndexOutOfBoundsException e) {
System.out.println("배열에서 벗어난 인덱스 사용");
e.printStackTrace();
}catch(NumberFormatException e) {
System.out.println("배열 인덱스형에 맞지 않는 자료형 사용");
e.printStackTrace();
}finally {
System.out.println("예외 발생 유무와 관련없이 항상 실행되는 코드");
}
System.out.println("정상 종료");
}

catch(Exception e)를 쓰면 모든 예외를 받아서 처리할 수 있음

=========================================================

//throw 강제로 예외를 발생시킬 수 있다.

int a=11;

try {

if(a>10) {

throw new Exception();

}else {

 

}

}catch(Exception e) {

System.out.println("a가 10보다 커서 예외 발생");

}

 =================================================================

//Throws 예제

public class MyThrows {

 

public static void test1() {

try {

System.out.println("hello");

throw new Exception();

}catch(Exception e) {

e.printStackTrace();

}

}

public static void test2() throws Exception { //함수호출한 사람이 예외처리해라

throw new Exception();

}

 

public static void main(String[] args) {

test1();

try {

test2();

} catch (Exception e) {

e.printStackTrace();

}

System.out.println("정상종료");

 

}