Lesson: Exception

1. Problem:

package az.etibarli;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int a = in.nextInt();
        int b = in.nextInt();
        System.out.println(a / b);
        System.out.println("Continue...");
    }
}

 -- Solution:

package az.etibarli;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int a = in.nextInt();
        int b = in.nextInt();
        try {
            System.out.println(a / b);
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println("Continue...");
    }
}

Demeli try-catch bloku iwletmedikde JVM exceptionu tutacaq printStackTrace() metodunu cagiracaq ve

sistemden cixacaq.

-- eslinde printStackTrace nece iwleyir:

package az.etibarli;

public class Main {
    public static void main(String[] args) {
        try {
            System.out.println(3 / 0);
        } catch (Exception e) {
            StackTraceElement[] elements = e.getStackTrace();
            System.err.println(e.getClass().getName() + ":" + e.getMessage());
            for (int i = 0; i < elements.length; i++) {
                StackTraceElement el = elements[i];
                System.err.println("\tat " + el.getMethodName() + "(" + el.getFileName() + ":" + el.getLineNumber() + ")");
            }
        }
    }
}

-- Oz exception class imizi yaratmaq:

*** An Exception is checked and RuntimeException is unchecked

package az.etibarli;

public class MyException extends Exception {

    public MyException(String message) {
        super(message);
    }
}

package az.etibarli;

public class Main {
    public static void main(String[] args) {
        String s = null;
        if (s == null) {
            try {
                throw new MyException("Xeta...");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

--

package az.etibarli;

public class MyException extends RuntimeException {

    public MyException(String message) {
        super(message);
    }
}

package az.etibarli;

public class Main {
    public static void main(String[] args) {
        String s = null;
        if (s == null) {
            throw new MyException("Xeta...");
        }
    }
}

-- Multiple catch:

package az.etibarli;

public class Main {
    public static void main(String[] args) {
        
        try {
            String s = null;
            System.out.println(s.length());
        } catch (ArithmeticException e) {
            System.out.println("Mathematical exception...");
        } catch (NullPointerException e) {
            System.out.println("Null pointer exception...");
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Array out of bounds exception...");
        } catch (Exception e) {
            System.out.println("Another type exception...");
        }
    }
}

Sonuncu catch blokunu ona gore yaziriq ki, yuxaridaki hec bir catch blokuna duwmese en azindan 

sonuncu bloka duwsun.

-- Yuxaridaki kodu qisaldaq:

package az.etibarli;

public class Main {
    public static void main(String[] args) {

        try {
            String s = null;
            System.out.println(s.length());
        } catch (ArithmeticException | NullPointerException | ArrayIndexOutOfBoundsException e) {
            System.out.println("Mathematical exception...");
        } catch (Exception e) {
            System.out.println("Another exception happened...");
        }
    }
}

-- Hem Exception-u hem de Error-u tutmaq ucun case:

package org.lesson7;

public class Main {
    public static void main(String[] args) {
        try {
            System.out.println(5 / 0);
        } catch (Throwable throwable) {
            throwable.printStackTrace();
        }
    }
}

-- throws

package org.example4;

public class Main {
    public static void main(String[] args) {

        try {
            throw new MyException("MyException...");
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println("Continue...");
    }
}

--

package org.example4;

public class MyException extends RuntimeException {

    public MyException(String message) {
        super(message);
    }
}

package org.example4;

public class Main {
    public static void main(String[] args) {

        throw new MyException("MyException...");
        System.out.println("Continue...");
    }
}

-- Unchecked exception: Yoxlamaq mecbur deyil.

package az.etibarli;

public class Main {
    public static void main(String[] args) {
        method();
    }

    public static void method() {
        throw new ArithmeticException();
    }
}

-- Checked exception: RuntimeException - dan extend etmir. Mecburuq yoxlamaga!

package az.etibarli;

import java.sql.SQLException;

public class Main {
    public static void main(String[] args) {
        method();
    }

    public static void method() {
        try {
            throw new SQLException();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

package az.etibarli;

import java.sql.SQLException;

public class Main {
    public static void main(String[] args) throws SQLException{
        method();
        System.out.println("Continue");
    }

    public static void method() throws SQLException{
        throw new SQLException();
    }
}