Variables, Conditionals and Exercises

Java 101 - Class 1

What we want to achieve

  • Exercises

  • Debugging

  • ืชื ืื™ ืžืงื•ืฆืจ - ternary conditional operator

  • MyConsole and Scanner

  • compilation and runtime errors

  • compiling and running via cmd/terminal

  • ื˜ื‘ืœืช ืžืขืงื‘ (ืžืฆื’ื•ืช)

What we learnt in class

  • ื—ืฉื‘ื•ืŸ ื•ืžื•ื“ืœื•

  • if and if-else

  • printing to screen System.out.println

  • while

  • Interger.MAX_VALUE

  • ื”ืžืจืช ืžืกืคืจื™ื ืžืžืžืฉื™ ืœื‘ื™ื ืจืื™ ื•ืœื”ื™ืคืš

Exercises

I0 - ืงืœื˜ ื•ืคืœื˜

ืคืœื˜ ื ืขืฉื” ืข"ื™ ื”ืคืงื•ื“ื”

System.out.println("hello ๐Ÿ‘‹")

ื‘ืจื•ื‘ ื”ide ื ื•ื›ืœ ืœื›ืชื•ื‘ syso ืื• sout ื›ื“ื™ ืฉื”ide ื™ืฉืœื™ื ืื•ืชื ื• ืื•ื˜ื•ืžื˜ื™ืช

ื‘ืงืœื˜ ื™ืฉ ืœื ื• 2 ื“ืจื›ื™ื

  • Scanner

  • MyConsole (ืžื” ืฉืœืžื“ื™ื ื‘ื”ืชื—ืœื” ื‘ืฉื™ืขื•ืจ)

MyConsole

public class Main {
    public static void main(String[] args) {
        int myInt = MyConsole.readInt("enter int: ");
        double myDouble = MyConsole.readDouble("enter double: ");
        String myString = MyConsole.readString("enter word: ");

        System.out.println("\nint is: " + myInt);
        System.out.println("double is: " + myDouble);
    }
}
enter int:  4.5
Not an integer. Please try again!
enter int:  7
enter double:  10.51

int is: 7
double is: 10.51
string is: hello

Scanner

Scanner scanner = new Scanner(System.in);
String myString = scanner.next();
int myInt = scanner.nextInt();
scanner.close();

System.out.println("myString is: " + myString);
System.out.println("myInt is: " + myInt);

input:

Hi 5

output:

myString is: Hi
myInt is: 5

Variables

ืžืฉืชื ื™ื ืคืจื™ืžื™ื˜ื™ื‘ื™ื

Image Source

public class Main {
    public static void main(String[] args) {
        byte tinyNum  =  100;
        short smallNum = 20_000;
        int num = 1<<20;
        long largeNum = (long) 1<<50;
        float decimal = 10.5050f;
        double largeDecimal = 3.141592653589;
        boolean trueOrFalse = true;

        System.out.println(num);
        System.out.println(largeNum);
        System.out.println(decimal);

        if (trueOrFalse)
            System.out.println("true");
        else
            System.out.println("false");
    }
}
1048576
1125899906842624
10.505
true

if and if else

ืชืจื’ื™ืœ: ืชื ืื™ื

Given an integer n , perform the following conditional actions:

  • If n is odd, print Strange

  • If n is even and in the inclusive range of 2 to 5 , print Not Strange

  • If n is even and in the inclusive range of 6 to 20, print Strange

  • If n is even and greater than 20, print Not Strange

Solution

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        System.out.print("Enter an integer: ");
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();

        if (n%2==1)
            System.out.println("Strange");
        else if (n%2==0 && n>=2 && n<=5)
            System.out.println("Not Strange");
        else if (n%2==0 && n>=6 && n<=20)
            System.out.println("Strange");
        else if (n%2==0 && n>20)
            System.out.println("Not Strange");
    }
}
Enter an integer: 20
Strange

ืชืจื’ื™ืœ: ื”ืื ื–ื” ืฉื ื” ืžืขื•ื‘ืจืช

ื›ืชื‘ื• ืชื•ื›ื ื™ืช ื”ืžื—ื–ื™ืจ ื”ืื ื”ืฉื ื” ื”ื•ื ืฉื ื” ืžืขื•ื‘ืจืช ืื• ืœื

To determine whether a year is a leap year, follow these steps:

  1. If the year is evenly divisible by 4, go to step 2. Otherwise, go to step 5.

  2. If the year is evenly divisible by 100, go to step 3. Otherwise, go to step 4.

  3. If the year is evenly divisible by 400, go to step 4. Otherwise, go to step 5.

  4. The year is a leap year (it has 366 days).

  5. The year is not a leap year (it has 365 days).

examples:

  • 1600 โœ”๏ธ leap year

  • 1700 โŒ not leap year

  • 1800 โŒ not leap year

  • 1900 โŒ not leap year

  • 2000 โœ”๏ธ leap year

  • 2001 โŒ not leap year

  • 2004 โœ”๏ธ leap year

package com.company;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("enter year: ");
        int year = sc.nextInt();

        boolean four = ((year % 4) == 0);
        boolean hundred = ((year % 100) == 0);
        boolean fourhundred = ((year % 400) == 0);
        boolean isleapyear = fourhundred || (four && !hundred);
        System.out.println(year + " is a leap year? " + isleapyear);
        sc.close();
    }
}
enter year: 2021
2021 is a leap year? false

ื‘ื ืขื›ืฉื™ื• ืœื’ืจื•ื ืœืชื•ื›ื ื™ืช ืœื ืœื”ืคืกืง

package com.company;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int year=-1;
        while (year!=0) {
            System.out.print("enter year: ");
            year = sc.nextInt();
            boolean four = ((year % 4) == 0);
            boolean hundred = ((year % 100) == 0);
            boolean fourhundred = ((year % 400) == 0);
            boolean isleapyear = fourhundred || (four && !hundred);
            System.out.println(year + " is a leap year? " + isleapyear);
        }
        sc.close();
    }
}
enter year: 2020
2020 is a leap year? true
enter year: 2021
2021 is a leap year? false
enter year: 0
0 is a leap year? true

ื›ืžื• ืฉื ื™ืชืŸ ืœืฉื™ื ืœื‘, ืขื˜ืคื ื• ืืช ื”ืชื•ื›ื ื™ืช ืฉืœื ื• ืขื while

while (year!=0) {
    ...
}

ืฉื™ื ืœื‘ ืฉืžื ื• ืืช Scanner ื‘ื—ื•ืฅ ื›ื›ื” ืœื ื ืฆื˜ืจืš ืคืขื ืœื™ื™ืฆืจ ืžืฉืชื ื” ื—ื“ืฉ ื›ืœ ืคืขื. ื‘ื ื•ืกืฃ ื’ื ื”ืกื’ื™ืจื” ืฉืœื• ื‘ื—ื•ืฅ

ืชืจื’ื™ืœื™ื: ื”ืžืจื•ืช

ืžื” ื™ื”ื™ื” ื”ืคืœื˜?

public class Main {
    public static void main(String[] args) {
        int x = 8, y = 13;
        double d = y/x;
        System.out.println("y/x = "+d);
        d = (double)y/x;
        System.out.println("y/x = "+d);
        double a = 5, b = 18;
        int c = (int)(a/b);
        System.out.println("a/b = "+c);
    }
}
y/x = 1.0
y/x = 1.625
a/b = 0

ืฉืืœื• ืืช ืขืฆืžื›ื ืœืžื” ื”ื”ื“ืคืกื” ื”ืจืืฉื•ื ื” ื™ื•ืฆื 1.0 ๐Ÿค”

ืžื” ื™ื”ื™ื” ื”ืคืœื˜?

public class Main {
    public static void main(String[] args) {
        double num = 123.45687;
        System.out.println((int)(num * 100) / 100.0);
    }
}
123.45

ืžื” ื™ื”ื™ื” ื”ืคืœื˜?

public class Main {
    public static void main(String[] args) {
        float x = (float)1.0, y = 3.0f, z=99;
        System.out.println(x/y);
        System.out.println(z);
    }
}
0.33333334
99.0

ื›ืืŸ ื”ื›ื–ืจื ื• ืขืœ 3 ืžืฉืชื ื™ float

ืœื•ืœื™ ื”ื™ื™ื ื• ืขื•ืฉื™ื ื›ื›ื” ื”ืงื•ื“ ืœื ืžืชืงืคืœ

float x = (float)1.0, y = 3.0, z=99;

ืœื ื”ื™ื” ืžืชืงืคืœ ื›ื™ ื” y ื”ื™ื” double. ืœื–ื” ืงื•ืจืื™ื compilation error

Runtime Error

public class Main {
    public static void main(String[] args) {
        System.out.println("Integer.MAX_VALUE = "+Integer.MAX_VALUE);
        System.out.println("Integer.MIN_VALUE = "+Integer.MIN_VALUE);
        System.out.println("Integer.SIZE = "+Integer.SIZE);
        int x = Integer.MAX_VALUE + 1;
        System.out.println("Integer.MAX_VALUE + 1 = "+x);
        int a = 0, b=10, z;
        z = b/a;
        System.out.println("b/a = "+z);
    }
}
Integer.MAX_VALUE = 2147483647
Integer.MIN_VALUE = -2147483648
Integer.SIZE = 32
Integer.MAX_VALUE + 1 = -2147483648
Exception in thread "main" java.lang.ArithmeticException: / by zero
    at com.company.Main.main(Main.java:11)

ืžืื•ื—ืจ ื™ื•ืชืจ ื ืœืžื“ ืขืœ try ื•catch ืฉื™ืขื–ืจื• ืœื ื• ืœื”ืชืžื•ื“ื“ ืขื ืฉื’ื™ืื•ืช

ืชืจื’ื™ืœ

ื›ืชื‘ื• ืื ืžืกืคืจ ื”ื•ื int, short or long

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        System.out.print("Enter an integer: ");
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();

        if (Short.MAX_VALUE>=n && Short.MIN_VALUE<=n)
            System.out.println("n is a: short");
        else if (Integer.MAX_VALUE>=n && Integer.MIN_VALUE<=n)
            System.out.println("n is an: int");
        else if (Long.MAX_VALUE>=n && Long.MIN_VALUE<=n)
            System.out.println("n is a: long");
    }
}
Enter an integer: 100000
n is an: int

ืžืกืคืจ ืฉืœื ืขื•ื‘ื“ ืœื ื•, ืื‘ืœ ืžื” ืงื•ืจื” ื‘ืžืกืคืจ ืžืžืฉื™

Enter an integer: 10.5
Exception in thread "main" java.util.InputMismatchException
    at java.base/java.util.Scanner.throwFor(Scanner.java:939)
    at java.base/java.util.Scanner.next(Scanner.java:1594)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
    at com.company.Main.main(Main.java:8)

ืงื™ื‘ืœื ื• Runtime error

ืขืœ ื”ื“ืจืš ื‘ื ื ื•ืกื™ืฃ ื’ื while ื›ื›ื” ืฉื›ืœ ืขื•ื“ ื”ืงืœื˜ ืื™ื ื• 0 ื”ื•ื ื™ืžืฉื™ืš ืœื‘ืงืฉ

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        System.out.print("Enter a number: ");
        Scanner scanner = new Scanner(System.in);
        double n = scanner.nextDouble();

        while (n!=0.) {
            if (Short.MAX_VALUE >= n && Short.MIN_VALUE <= n && n % 1 == 0.) {
                System.out.println(n + " can fit in a: ");
                System.out.println("* short\n* int\n* long\n");
            } else if (Integer.MAX_VALUE >= n && Integer.MIN_VALUE <= n && n % 1 == 0.) {
                System.out.println(n + " can fit in a: ");
                System.out.println("* int\n* long\n");
            } else if (Long.MAX_VALUE >= n && Long.MIN_VALUE <= n && n % 1 == 0.)
                System.out.println(n + " can fit in a: \n* long\n");
            else if ((Float.MAX_VALUE >= n && Float.MIN_VALUE <= n) || (Double.MAX_VALUE >= n && Double.MIN_VALUE <= n))
                System.out.println("n is either a: float, double\n");

            //receive next input
            System.out.print("Enter a number: ");
            n = scanner.nextDouble();
        }

        scanner.close();
    }
}
Enter a number: 10.5
n is either a: float, double

Enter a number: 1000000
1000000.0 can fit in a: 
* int
* long

Enter a number: 0

ื’ื ื”ื™ื™ื ื• ื™ื›ื•ืœ ืœืขืฉื•ืช && ((short) n) == n ื• ((int) n) == n ื‘ืชื ืื™

ื™ืฉ ืœื–ื” ื‘ื™ืฆื•ืขื™ื ื™ื•ืชืจ ื’ื‘ื•ื”ื”ื™ื

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