자바 try, catch, finally, exception

package test;

class MyDate {

int year = 2018;

}

public class Test1 {

public static void main(String[] args) {

System.out.println("==시작==");

MyDate myDate = null;

try {

System.out.println(myDate.year);

} catch (Exception e) {

System.out.println("예외발생");

System.out.println(e);

System.out.println(e.toString());

System.out.println(e.getMessage());

e.printStackTrace();

}

System.out.println("==종료==");

} // main()

}

package test;

public class Test2 {

public static void main(String[] args) {

System.out.println("==시작==");

int[] num = {1, 2, 3};

// alt shift z y

try {

num[10] = 5;

} catch (Exception e) {

e.printStackTrace();

}

System.out.println("==종료==");

} // main()

}

package test;

import java.util.List;

public class Test3 {

void methodA() throws Exception {

System.out.println("methodA() 시작");

methodB();

System.out.println("methodA() 종료");

}

void methodB() throws RuntimeException {

System.out.println("methodB() 시작");

methodC();

System.out.println("methodB() 종료");

} // methodB()

void methodC() throws ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException {

System.out.println("methodC() 시작");

int num = 0;

int result = 10 / num;  // 0으로 나눔

List list = null;

list.add("문자열");  // 널포인터 예외

int[] arr = {1, 2, 3};

arr[5] = 10;  // 인덱스범위초과 예외

System.out.println("methodC() 종료");

} // methodC()

public static void main(String[] args) {

System.out.println("main() 시작");

Test3 t = new Test3();

try {

t.methodA();

} catch (Exception e) {

e.printStackTrace();

}

System.out.println("main() 종료");

} // main()

}

package test;

import java.util.Scanner;

class Dog {

int age;

public void setAge(int age) throws Exception {

System.out.println("age = " + age);

if (age < 0) {

// 예외를 인위적으로 발생

throw new Exception("age값이 0보다 작습니다.");

}

}

public int getAge() {

// try-catch-finally에서 catch블록이 있으면 예외처리가 목적임.

// try-finally 예외처리가 목적이 아님!

Scanner scanner = new Scanner(System.in);

try {

return age;

} finally {

System.out.println("finally 블록");

scanner.close();

}

} // getAge();

}

public class Test4 {

public static void main(String[] args) {

System.out.println("main() 시작");

Dog dog = new Dog();

try {

dog.setAge(-5);

} catch (Exception e) {

e.printStackTrace();

}

System.out.println(dog.getAge());

System.out.println("main() 종료");

} // main()

}