Practice Questions — Variables and Data Types in Java

public class DataTypeExplorer {
    public static void main(String[] args) {
        byte b = 42;
        short s = 2026;
        int i = 100000;
        long l = 9876543210L;
        float f = 3.14f;
        double d = 2.718281828;
        char c = 'A';
        boolean bool = true;

        System.out.println("byte value: " + b + " (size: " + Byte.SIZE/8 + " byte)");
        System.out.println("short value: " + s + " (size: " + Short.SIZE/8 + " bytes)");
        System.out.println("int value: " + i + " (size: " + Integer.SIZE/8 + " bytes)");
        System.out.println("long value: " + l + " (size: " + Long.SIZE/8 + " bytes)");
        System.out.println("float value: " + f + " (size: " + Float.SIZE/8 + " bytes)");
        System.out.println("double value: " + d + " (size: " + Double.SIZE/8 + " bytes)");
        System.out.println("char value: " + c + " (size: " + Character.SIZE/8 + " bytes)");
        System.out.println("boolean value: " + bool);
    }
}

public class TempConverter {
    public static void main(String[] args) {
        double celsius = 37.5;
        double fahrenheit = celsius * 9.0 / 5 + 32;
        double kelvin = celsius + 273.15;
        System.out.printf("Celsius: %.2f%n", celsius);
        System.out.printf("Fahrenheit: %.2f%n", fahrenheit);
        System.out.printf("Kelvin: %.2f%n", kelvin);
    }
}

public class CastingChain {
    public static void main(String[] args) {
        double d = 99.99;
        float f = (float) d;
        long l = (long) d;
        int i = (int) d;
        short s = (short) d;
        byte b = (byte) d;
        System.out.println("Original double: " + d);
        System.out.println("As float: " + f);
        System.out.println("As long: " + l + " (decimal truncated)");
        System.out.println("As int: " + i + " (decimal truncated)");
        System.out.println("As short: " + s);
        System.out.println("As byte: " + b);
        System.out.println("\nNow with 999.99:");
        d = 999.99;
        System.out.println("double: " + d);
        System.out.println("As byte: " + (byte) d + " (overflow!)");
    }
}

public class GradeCalculator {
    public static void main(String[] args) {
        int m1 = 85, m2 = 92, m3 = 78, m4 = 95, m5 = 88;
        int total = m1 + m2 + m3 + m4 + m5;
        double percentage = (double) total / 5;
        double average = percentage;
        char grade;
        if (percentage >= 90) grade = 'O';
        else if (percentage >= 80) grade = 'A';
        else if (percentage >= 70) grade = 'B';
        else if (percentage >= 60) grade = 'C';
        else grade = 'F';
        System.out.println("Marks: " + m1 + " " + m2 + " " + m3 + " " + m4 + " " + m5);
        System.out.println("Total: " + total);
        System.out.printf("Percentage: %.2f%%%n", percentage);
        System.out.printf("Average: %.2f%n", average);
        System.out.println("Grade: " + grade);
    }
}

public class AsciiTable {
    public static void main(String[] args) {
        System.out.println("=== Uppercase Letters ===");
        for (char c = 'A'; c <= 'Z'; c++) {
            System.out.print(c + "=" + (int) c + " ");
            if ((c - 'A' + 1) % 10 == 0) System.out.println();
        }
        System.out.println("\n\n=== Lowercase Letters ===");
        for (char c = 'a'; c <= 'z'; c++) {
            System.out.print(c + "=" + (int) c + " ");
            if ((c - 'a' + 1) % 10 == 0) System.out.println();
        }
        System.out.println();
    }
}

public class OverflowDetector {
    public static void main(String[] args) {
        byte maxByte = Byte.MAX_VALUE;
        short maxShort = Short.MAX_VALUE;
        int maxInt = Integer.MAX_VALUE;
        System.out.println("byte MAX + 1: " + maxByte + " + 1 = " + (byte)(maxByte + 1));
        System.out.println("short MAX + 1: " + maxShort + " + 1 = " + (short)(maxShort + 1));
        System.out.println("int MAX + 1: " + maxInt + " + 1 = " + (maxInt + 1));
        System.out.println();
        int intResult = 100000 * 100000;
        long longResult = 100000L * 100000;
        System.out.println("int multiplication: 100000 * 100000 = " + intResult + " (WRONG - overflow!)");
        System.out.println("long multiplication: 100000 * 100000 = " + longResult + " (correct)");
    }
}

public class WrapperUtility {
    public static void main(String[] args) {
        System.out.println("=== Parsing ===");
        int parsed = Integer.parseInt("42");
        double parsedD = Double.parseDouble("3.14");
        System.out.println("\"42\" -> " + parsed);
        System.out.println("\"3.14\" -> " + parsedD);
        System.out.println("\n=== Ranges ===");
        System.out.println("int: [" + Integer.MIN_VALUE + ", " + Integer.MAX_VALUE + "]");
        System.out.println("long: [" + Long.MIN_VALUE + ", " + Long.MAX_VALUE + "]");
        System.out.println("\n=== Number Conversions ===");
        System.out.println("255 binary: " + Integer.toBinaryString(255));
        System.out.println("255 hex: " + Integer.toHexString(255));
        System.out.println("255 octal: " + Integer.toOctalString(255));
        System.out.println("\n=== Character Utilities ===");
        System.out.println("'A' isLetter: " + Character.isLetter('A'));
        System.out.println("'5' isDigit: " + Character.isDigit('5'));
        System.out.println("'a' toUpperCase: " + Character.toUpperCase('a'));
        System.out.println("'Z' toLowerCase: " + Character.toLowerCase('Z'));
        System.out.println("' ' isWhitespace: " + Character.isWhitespace(' '));
    }
}

public class PrecisionDemo {
    public static void main(String[] args) {
        // float has ~7 decimal digits precision
        float f1 = 1.0f / 3;
        float f2 = 2.0f / 3;
        // double has ~15 decimal digits precision
        double d1 = 1.0 / 3;
        double d2 = 2.0 / 3;
        System.out.println("float 1/3: " + f1);
        System.out.println("double 1/3: " + d1);
        System.out.println("float 2/3: " + f2);
        System.out.println("double 2/3: " + d2);
        // The 0.1 + 0.2 problem
        // 0.1 and 0.2 cannot be represented exactly in binary
        // floating-point, leading to tiny rounding errors
        System.out.println("\n0.1 + 0.2 = " + (0.1 + 0.2));
        System.out.println("0.1 + 0.2 == 0.3? " + (0.1 + 0.2 == 0.3));
        System.out.println("\nFor financial calculations, use BigDecimal.");
    }
}