#Java Numbers and Math Class

Java not only provides primitive data types (such as int, double) to handle numbers, but also offers a series of Wrapper Classes and a powerful Math class for more complex operations and calculations.

#Number Wrapper Classes

For each primitive data type, Java provides a corresponding wrapper class. These classes "wrap" primitive types into objects, giving them more functionality, such as type conversion or participation in object-oriented operations (like storing in generic collections).

#Autoboxing and Unboxing

Starting from Java 5, Java introduced autoboxing and unboxing mechanisms, making the conversion between primitive types and wrapper classes seamless.

• Autoboxing: Automatically converts a primitive type to its corresponding wrapper class object.
• Unboxing: Automatically converts a wrapper class object to its corresponding primitive type.

// Autoboxing: int is automatically converted to Integer
Integer myIntObject = 100;

// Unboxing: Integer is automatically converted to int
int myIntPrimitive = myIntObject;

System.out.println(myIntObject.getClass().getName()); // Output: java.lang.Integer
System.out.println(myIntPrimitive); // Output: 100

#Common Wrapper Class Methods

Wrapper classes provide many useful static and instance methods.

• parseXXX(): Converts a string to the corresponding primitive type (e.g., Integer.parseInt("123")).
• valueOf(): Converts a string or primitive type to the corresponding wrapper class object.
• toString(): Converts a number to a string.
• Comparison: equals() is used to compare whether the values of two objects are equal; compareTo() is used to compare the magnitude of two numbers.

public class WrapperClassExample {
    public static void main(String[] args) {
        // Use parseInt() to convert string to int
        String strNumber = "250";
        int number = Integer.parseInt(strNumber);
        System.out.println("Parsed integer: " + number);

        // Use valueOf() to get an Integer object
        Integer anotherNumber = Integer.valueOf("500");

        // Use compareTo() to compare values
        // Return value < 0: anotherNumber is less than 1000
        // Return value = 0: anotherNumber equals 1000
        // Return value > 0: anotherNumber is greater than 1000
        System.out.println(anotherNumber.compareTo(1000)); // Outputs negative number

        // Get Integer max and min value constants
        System.out.println("Integer max value: " + Integer.MAX_VALUE);
        System.out.println("Integer min value: " + Integer.MIN_VALUE);
    }
}

#Math Class

The java.lang.Math class contains a series of static methods for performing basic mathematical operations, such as exponentials, logarithms, square roots, and trigonometric functions. You don't need to create an instance of the Math class; simply call its methods directly through the class name.

#Common Math Methods

• Math.abs(x): Returns the absolute value of x.
• Math.max(a, b): Returns the larger of a and b.
• Math.min(a, b): Returns the smaller of a and b.
• Math.sqrt(x): Returns the positive square root of x.
• Math.pow(a, b): Returns a raised to the power of b (a^b).
• Math.round(x): Returns the rounded long or int value of x.
• Math.ceil(x): Returns the smallest integer greater than or equal to x (ceiling).
• Math.floor(x): Returns the largest integer less than or equal to x (floor).
• Math.random(): Returns a random double value in the range [0.0, 1.0).

#Trigonometric Functions

• Math.sin(a), Math.cos(a), Math.tan(a): The parameter a is an angle in radians.
• Math.toDegrees(rad): Converts radians to degrees.
• Math.toRadians(deg): Converts degrees to radians.

Example:

public class MathExample {
    public static void main(String[] args) {
        double x = 25.0;
        double y = -10.5;

        System.out.println("Square root of 25 is: " + Math.sqrt(x)); // 5.0
        System.out.println("2 to the power of 8 is: " + Math.pow(2, 8)); // 256.0
        System.out.println("Absolute value of -10.5 is: " + Math.abs(y)); // 10.5
        System.out.println("Ceiling of 4.3: " + Math.ceil(4.3)); // 5.0
        System.out.println("Floor of 4.7: " + Math.floor(4.7)); // 4.0
        System.out.println("Rounding 4.5: " + Math.round(4.5)); // 5

        // Generate a random integer between 1 and 10
        int randomNumber = (int)(Math.random() * 10) + 1;
        System.out.println("Random number 1-10: " + randomNumber);

        // Calculate the sine of 90 degrees
        double angleInDegrees = 90.0;
        double angleInRadians = Math.toRadians(angleInDegrees);
        System.out.println("sin(90 degrees) = " + Math.sin(angleInRadians)); // 1.0
    }
}