Wetofu

Exception & Assertion

EXCEPTION

• Represents an error condition that can occur during the normal course of program execution
• exception handling increase robustness

EXCEPTION HANDLING

• When an exception occurs -> the normal sequence of flow is terminated and the exception-handling routine is executed
• Exception occurs -> exeption is thrown
• Exception-handling code is executed -> exception is caught

try {
	// Block of code to try
}
catch(Exception e){
	// Block of code to handle errors
}

TYPE OF EXCEPTIONS

• Checked :
• checked at compile time
• Unchecked / runtime exceptions :
• unchecked at compile time and are detected only at runtime

ASSERTIONS

• A language feature we use to detect logical errors in a program
• display logical error when compilling

TYPE OF ASSERTION

• Postconditon assertion :
• checks for a condition that must be true after a method is executed

</ul>
<li>Precondition assertion :</li> 
<ul>
    <li>a checking of condition that must be true before a method is executed</li> 

</ul>
<li>Control flow invariant</li> 



SOURCE CODE :

    Execption :

package oop.exceptions;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Scanner;
// program mencari tahun lahir berdasarkan usia
public class AgeInput1 {
public int getAge(String prompt, Scanner scanner) {
System.out.print(prompt);
int age = scanner.nextInt();
return age;
}
public static void main(String[] args) {
GregorianCalendar today;
int age, thisYear, bornYr;
String answer;
Scanner scanner = new Scanner(System.in);
AgeInput1 input = new AgeInput1();
age = input.getAge("How old are you? ", scanner);
today = new GregorianCalendar();
thisYear = today.get(Calendar.YEAR);
bornYr = thisYear - age;
System.out.print("Already had your birthday this year? (Y or N)");
answer = scanner.next();
if (answer.equals("N") || answer.equals("n")) {
bornYr--;
}
System.out.println("\nYou are born in " + bornYr);
}
}

package oop.exceptions;

import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.InputMismatchException;
import java.util.Scanner;

public class AgeInput2 {
    public int getAge(String prompt, Scanner scanner) {
        int age = 0;
        boolean keepGoing = true;
        while (keepGoing) {
            System.out.print(prompt);
            try {
                age = scanner.nextInt();
                keepGoing = false;
            } catch (InputMismatchException e) {
                scanner.next(); // remove the leftover garbage
                // from the input buffer
                System.out.println("Invalid Entry.Please enter digits only.");
            }
        }
        return age;
    }

    public static void main(String[] args) {
        GregorianCalendar today;
        int age, thisYear, bornYr;
        String answer;
        
        Scanner scanner = new Scanner(System.in);
        AgeInput2 input = new AgeInput2();
        age = input.getAge("How old are you? ", scanner);
        today = new GregorianCalendar();
        thisYear = today.get(Calendar.YEAR);
        bornYr = thisYear - age;
        
        System.out.print("Already had your birthday this year? (Y or N)");
        answer = scanner.next();
        if (answer.equals("N") || answer.equals("n")) {
            bornYr--;
        }
        System.out.println("\nYou are born in " + bornYr);
    }
}

package oop.exceptions;

import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.InputMismatchException;
import java.util.Scanner;

public class AgeInput3 {
	public int getAge(String prompt, Scanner scanner) {
		int age = 0;
		while (true) {
			System.out.print(prompt);
			try {
				age = scanner.nextInt();
				if (age < 0) {
					throw new Exception("Negative age is invalid");
				}
				return age;
			} catch (InputMismatchException e) {
				scanner.next(); // remove the leftover garbage
				// from the input buffer
				System.out.println("Invalid Entry.Please enter digits only.");
			} catch (Exception e) {
				System.out.println("Error: " + e.getMessage());
			}
		}
	}

	public static void main(String[] args) {
		GregorianCalendar today;
		int age, thisYear, bornYr;
		String answer;
		
		Scanner scanner = new Scanner(System.in);
		AgeInput3 input = new AgeInput3();
		age = input.getAge("How old are you? ", scanner);
		today = new GregorianCalendar();
		thisYear = today.get(Calendar.YEAR);
		bornYr = thisYear - age;
		
		System.out.print("Already had your birthday this year? (Y or N)");
		answer = scanner.next();
		if (answer.equals("N") || answer.equals("n")) {
			bornYr--;
		}
		System.out.println("\nYou are born in " + bornYr);
	}
}

package oop.exceptions;

import java.util.InputMismatchException;
import java.util.Scanner;

public class AgeInput4 {
	private static final String DEFAULT_MESSAGE = "Your age:";
	private static final int DEFAULT_LOWER_BOUND = 0;
	private static final int DEFAULT_UPPER_BOUND = 99;

	private int lowerBound;
	private int upperBound;
	private Scanner scanner;

	public AgeInput4() {
		init(DEFAULT_LOWER_BOUND, DEFAULT_UPPER_BOUND);
	}

	public AgeInput4(int low, int high) throws IllegalArgumentException {
		if (low > high) {
			throw new IllegalArgumentException("Low (" + low + ") was " + "larger than high(" + high + ")");
		} else {
			init(low, high);
		}
	}

	public int getAge() throws Exception {
		return getAge(DEFAULT_MESSAGE);

	}

	public int getAge(String prompt) throws Exception {
		int age;
		while (true) {
			System.out.print(prompt);
			try {
				age = scanner.nextInt();
				if (age < lowerBound || age > upperBound) {
					throw new Exception("Input out of bound");
				}
				return age; // input okay so return the value & exit
			} catch (InputMismatchException e) {
				scanner.next();
				System.out.println("Input is invalid.\n" + "Please enter digits only");
			}
		}
	}

	private void init(int low, int high) {
		lowerBound = low;
		upperBound = high;
		scanner = new Scanner(System.in);
	}
}

package oop.exceptions;

import java.util.InputMismatchException;
import java.util.Scanner;

public class AgeInput5 {
	private static final String DEFAULT_MESSAGE = "Your age:";
	private static final int DEFAULT_LOWER_BOUND = 0;
	private static final int DEFAULT_UPPER_BOUND = 99;

	private int lowerBound;
	private int upperBound;
	private Scanner scanner;

	public AgeInput5() {
		init(DEFAULT_LOWER_BOUND, DEFAULT_UPPER_BOUND);
	}

	public AgeInput5(int low, int high) throws IllegalArgumentException {
		if (low > high) {
			throw new IllegalArgumentException("Low (" + low + ") was " + "larger than high(" + high + ")");
		} else {
			init(low, high);
		}
	}

	public int getAge() throws Exception {
		return getAge(DEFAULT_MESSAGE);

	}

	public int getAge(String prompt) throws AgeInputException {
		int age;
		while (true) {
			System.out.print(prompt);
			try {
				age = scanner.nextInt();
				if (age < lowerBound || age > upperBound) {
					throw new AgeInputException("Input out of bound", 0, 99, age);
				}
				return age; // input okay so return the value & exit
			} catch (InputMismatchException e) {
				scanner.next();
				System.out.println("Input is invalid.\n" + "Please enter digits only");
			}
		}
	}

	private void init(int low, int high) {
		lowerBound = low;
		upperBound = high;
		scanner = new Scanner(System.in);
	}
}

package oop.exceptions;

public class AgeInputException extends Exception {
	private static final String DEFAULT_MESSAGE = "Input out of bounds";
	private int lowerBound;
	private int upperBound;
	private int value;

	public AgeInputException(int low, int high, int input) {
		this(DEFAULT_MESSAGE, low, high, input);
	}

	public AgeInputException(String msg, int low, int high, int input) {
		super(msg);
		if (low > high) {
			throw new IllegalArgumentException();
		}
		lowerBound = low;
		upperBound = high;
		value = input;
	}

	public int lowerBound() {
		return lowerBound;
	}

	public int upperBound() {
		return upperBound;
	}

	public int value() {
		return value;
	}
}

package oop.exceptions;

import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Scanner;

public class TestAgeInput4 {
	public static void main(String[] args) {
		GregorianCalendar today;
		int age = 0, thisYear, bornYr;
		String answer;
		
		Scanner scanner = new Scanner(System.in);
		AgeInput4 input = new AgeInput4();
		try {
			age = input.getAge("How old are you? ");
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		today = new GregorianCalendar();
		thisYear = today.get(Calendar.YEAR);
		bornYr = thisYear - age;
		
		System.out.print("Already had your birthday this year? (Y or N)");
		answer = scanner.next();
		if (answer.equals("N") || answer.equals("n")) {
			bornYr--;
		}
		System.out.println("\nYou are born in " + bornYr);
	}
}

package oop.exceptions;

import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Scanner;

public class TestAgeInput5 {
	public static void main(String[] args) {
		GregorianCalendar today;
		int age = 0, thisYear, bornYr;
		String answer;
		
		Scanner scanner = new Scanner(System.in);
		AgeInput5 input = new AgeInput5();
		try {
			age = input.getAge("How old are you? ");
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		today = new GregorianCalendar();
		thisYear = today.get(Calendar.YEAR);
		bornYr = thisYear - age;
		
		System.out.print("Already had your birthday this year? (Y or N)");
		answer = scanner.next();
		if (answer.equals("N") || answer.equals("n")) {
			bornYr--;
		}
		System.out.println("\nYou are born in " + bornYr);
	}
}

Assertion :

package oop.assertions;

public class BankAccount {
	private double balance;

	public BankAccount(double initialBalance) {
		balance = initialBalance;
	}

	public void deposit(double amount) {
		double oldBalance = balance;
		balance -= amount;
		assert balance > oldBalance;
	}

	public void withdraw(double amount) {
		double oldBalance = balance;
		balance -= amount;
		assert balance < oldBalance;
	}

	public double getBalance() {
		return balance;
	}

	public static void main(String[] args) {
		BankAccount acct = new BankAccount(200);
		acct.deposit(25);
		System.out.println("Current Balance: " + acct.getBalance());
	}
}