Java – Custom Exceptions – Ameerpet Technologies

Custom Exceptions:

Defining a class by extending from Exception is called Custom Exception.
Examples:
- InvalidAgeException
- LowBalanceException

Defining Custom Exception:

class MyException extends Exception
{
// body;
}

throw:

Pre-defined exceptions automatically raised when error occurred.
Custom exceptions must be raised manually by the programmer using throw-keyword.

LowBalanceException obj = new LowBalanceException(“Low Balance in Account”);
throw obj;

throws:

‘throws’ is used to describe the exception which may raise in Method logic.
Prototype of method specifies the Exception type.
We handle that exception when we invoke the method.

String to int conversion:

parseInt() is a pre-defined method that converts String to int
parseInt() raises Exception if the input is non-convertible integer.

Pre-defined Method as follows:

class Integer
{
	public static int parseInt(String s) throws NumberFormatException
	{
		logic;
	}
}

Method-1: we can handle using try-catch while using method.

static void main()
{
	String s = "abc";
	try{
		int x = Integer.parseInt(s);
	}
	catch(NumberFormatException e){
		System.out.println("Invalid string");
	}
}

Method-2: throws the same exception without handling

static void main() throws NumberFormatException
{
	String s = "abc";
	int x = Integer.parseInt(s);
}

InvalidAgeException:

import java.util.Scanner;
class InvalidAgeException extends Exception
{
            InvalidAgeException(String name){
                        super(name);
            }
}

class Person
{
            static void canVote(int age) throws InvalidAgeException{
                        if(age>=18){
                                    System.out.println(“Can vote”);
                        }
                        else{
                                    InvalidAgeException obj = new InvalidAgeException(“Invalid Age”);
                                    throw obj;
                        }
            }
}

class Main
{
            public static void main(String[] args){
                        System.out.print(“Enter age : “);
                        Scanner sc = new Scanner(System.in);
                        int age = sc.nextInt();
                        try{
                                    Person.canVote(age);
                        }
                        catch (InvalidAgeException e){
                                    System.out.println(“Exception : ” + e.getMessage());
                        }
            }
}

LowBalanceException:

import java.util.Scanner;
class LowBalanceException extends Exception
{
            LowBalanceException(String name) {
                        super(name);
            }
}
class Account
{
            int balance;
            Account(int balance) {
                        this.balance = balance;
            }

            void withdraw(int amount) throws LowBalanceException {
                        if(amount <= this.balance) {
                                    System.out.println(“Collect cash : ” + amount);
                                    this.balance = this.balance – amount;
                        }
                        else {
                                    LowBalanceException obj = new LowBalanceException(“Low balance”);
                                    throw obj;
                        }
            }
}

class Bank
{
            public static void main(String[] args) {
                        Scanner sc = new Scanner(System.in);
                        System.out.print(“Enter initial balance : “);
                        int amount = sc.nextInt();

                        Account acc = new Account(amount);
                        System.out.println(“Account created with balance : ” + acc.balance);

                        System.out.print(“Enter withdraw amount : “);
                        amount = sc.nextInt();

                        try {
                                    acc.withdraw(amount);
                        }
                        catch (LowBalanceException e) {
                                    System.out.println(“Exception : ” + e.getMessage());
                        }
                        System.out.println(“Final balance : ” + acc.balance);
            }
}

Java – Custom Exceptions

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