✅ 이것만은 꼭 정리해놓자!
try {
// code to be monitored for exceptions goes here
} catch (IOException e) {
System.err.println("An IO error occurred: " + e.getMessage());
} catch (Exception e) {
System.err.println("An error occurred: " + e.getMessage());
e.printStackTrace();
} finally {
// code to be executed regardless of whether an exception occurred or not goes here
}ArithmeticException
This exception is thrown when an arithmetic operation results in an overflow, underflow, or
division by zero.
NullPointerException - This exception is thrown when you try to access an object or variable
that is null.
ArrayIndexOutOfBoundsException - This exception is thrown when you try to access an array
element with an invalid index.
ClassCastException - This exception is thrown when you try to cast an object to a type that is
not compatible with its actual type.
NumberFormatException - This exception is thrown when you try to convert a string to a numeric
value, but the string does not represent a valid number.
IOException - This exception is thrown when an I/O error occurs, such as when reading or
writing a file.
SQLException - This exception is thrown when an error occurs while working with a database.
InterruptedException - This exception is thrown when a thread is interrupted while it is
waiting, sleeping, or performing some other blocking operation.
RuntimeException - This is a general-purpose exception that can be thrown for a wide variety
of runtime errors.try 는 필수 구문이고 catch는 선택이다. 하지만 catch를 써야지만 에러가 발생했을 때 이를 핸들링 할 수 있다. java의 대표적인 error에는 아래와 같은 에러가 있다. finally 구문은 에러와 상관 없이 기본적으로 실행되는 부문이다.
✅ 이것만은 꼭 정리해놓자!
Exception 만들기
new Exception()
public class CustomException extends Exception {
public CustomException(String message) {
super(message);
}
}
public class example {
public void doSomething() throws CustomException {
if (true) {
throw new CustomException("Something went wrong.");
}
}
}
new RunTimeException()
public class test {
public void doSomething() {
// some code that may throw CustomException
if (true) {
throw new RuntimeException("Something went wrong.");
}
}
}
throw 문법
public class Main {
public static void main(String[] args) {
try {
int result = divide(10, 0);
System.out.println("Result: " + result);
} catch (RuntimeException e) {
System.out.println("Caught a RuntimeException: " + e.getMessage());
}
}
public static int divide(int dividend, int divisor) {
if (divisor == 0) {
throw new RuntimeException("Divisor cannot be zero.");
}
return dividend / divisor;
}
}
📖 연습 문제) equals(), hashCode()
public class Money {
private int value;
public Money(int value) {
this.value = value;
}
private int getValue(Money money) {
return money.value;
}
@Override
public boolean equals(Object o) {
if (getClass() != o.getClass()) {
return false;
}
Money m = (Money) (o);
if (this.value == m.getValue(m)) {
return true;
}
return false;
}
}
🎯 문자 말고 숫자만 입력하라구!
package OnlyNumber;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
boolean isContinued = true;
while (isContinued) {
System.out.println("숫자를 입력해주세요.");
String input = scanner.nextLine();
int number;
try {
number = Integer.parseInt(input);
System.out.println("입력하신 숫자는 " + number + "입니다.");
} catch (NumberFormatException e) {
System.out.println("잘못된 값을 입력하셨습니다.");
}
}
}
}
🎯 휴대폰 번호 입력받기 v1
package ex6.PhoneNumberV1;
interface TypeCheck {
public void checkIsAllDigits(String phoneNumber);
public void checkFirstThreeDigits(String phoneNumber);
public void checkTotalLength(String phoneNumber);
}package ex6.PhoneNumberV1;
import java.util.Scanner;
public class Input {
Scanner sc = new Scanner(System.in);
String inputPhoneNumber() {
System.out.println("휴대폰 번호를 입력해주세요.");
String phoneNumber = sc.nextLine();
return phoneNumber;
}
}package ex6.PhoneNumberV1;
public class PhoneNumber implements TypeCheck {
private String value;
public PhoneNumber() {
Input input = new Input();
String phoneNumber = input.inputPhoneNumber();
this.validate(phoneNumber);
this.value = phoneNumber;
}
private void validate(String phoneNumber) {
checkIsAllDigits(phoneNumber);
checkFirstThreeDigits(phoneNumber);
checkTotalLength(phoneNumber);
getPhoneNumberFormally(phoneNumber);
}
@Override
public void checkIsAllDigits(String phoneNumber) {
for (int i = 0; i < phoneNumber.length(); i++) {
try {
Integer.parseInt(String.valueOf(phoneNumber.charAt(i)));
} catch (IllegalArgumentException e) {
throw new IllegalArgumentException("숫자를 입력해주세요.");
}
}
}
@Override
public void checkFirstThreeDigits(String phoneNumber) {
if (!phoneNumber.startsWith("010")) {
throw new IllegalArgumentException("휴대폰 번호는 010으로 시작해야 합니다.");
}
}
@Override
public void checkTotalLength(String phoneNumber) {
int totalLength = 0;
for (int i = 0; i < phoneNumber.length(); i++) {
totalLength += 1;
}
if (totalLength != 11) {
throw new IllegalArgumentException("휴대폰 번호는 11글자여야 합니다.");
}
}
private void getPhoneNumberFormally(String phoneNumber) {
String res = "";
for (int i = 0; i < phoneNumber.length(); i++) {
if (i == 3 || i == 7) {
res += "-";
}
res += phoneNumber.charAt(i);
}
System.out.println("휴대폰 번호를 정상적으로 입력하셨습니다. 입력하신 휴대폰 번호는 " + res + "입니다.");
}
}package ex6.PhoneNumberV1;
public class Main {
public static void main(String[] args) {
new PhoneNumber();
}
}🎯 휴대폰 번호 입력받기 v2
package ex6.PhoneNumberV2;
import java.util.Scanner;
public class PhoneNumber {
private String value;
public PhoneNumber() {
this.value = this.checkFormat();
}
private String getPhoneNumberFormally(String ValidPhoneNumber) {
String res = "";
for (int i = 0; i < ValidPhoneNumber.length(); i++) {
if (i == 3 || i == 7) {
res += "-";
}
res += ValidPhoneNumber.charAt(i);
}
return res;
}
String checkFormat() {
System.out.println("휴대폰 번호를 입력해주세요.");
Scanner sc = new Scanner(System.in);
String phoneNumber = sc.nextLine();
// 입력 받은 문자열이 모두 숫자인지 확인
for (int i = 0; i < phoneNumber.length(); i++) {
try {
char num = phoneNumber.charAt(i);
Integer.parseInt(String.valueOf(num));
} catch (NumberFormatException e) {
System.out.println("숫자만 입력해주세요.");
return checkFormat();
}
}
// 핸드폰 번호 자릿수 확인
if (phoneNumber.length() != 11) {
System.out.println(phoneNumber.length());
System.out.println("휴대폰 번호는 11글자여야 합니다.");
return checkFormat();
}
// 입력 받은 문자열의 앞부분이 010인지 확인
if (!phoneNumber.startsWith("010")) {
System.out.println("휴대폰 앞자리는 010 이어야 합니다.");
return checkFormat();
}
System.out.println(
"휴대폰 번호를 정상적으로 입력하셨습니다. 입력하신 휴대폰 번호는 " + getPhoneNumberFormally(phoneNumber) + "입니다.");
return phoneNumber;
}
}package ex6.PhoneNumberV2;
public class Main {
public static void main(String[] args) throws Exception {
new PhoneNumber();
}
}