Java Methods and Math Class

Methods

Java's methods are reusable blocks of code.
Math methods often use double arguments.
String methods are used for string manipulation.
Boolean variables hold true or false values.
Java methods can accept parameters and return values.
Class methods are associated with the class.
Instance methods are associated with objects.
Methods can be created to perform specific tasks.
A method library is a collection of organized and reusable methods.

Objectives

Using Math methods.
Understanding string methods.
Understanding the boolean type.
Creating custom Java methods.
Defining and using parameters with methods.
Differentiating between class and instance methods.
Building a method library.

Java's Math Class

Provides a set of pre-built mathematical functions.
Part of the Java.lang package, so no import needed.
Uses static methods, so no need to create an object.
Math methods typically take double arguments.
Math class includes constants like Math.E and Math.PI.
Example: Calculating the volume of a sphere using radius.
- Formula: volume = (4/3) * π * radius³
- Implementation: double volume = 4.0 / 3.0 * Math.PI * Math.pow(radius, 3.0);

Math Class Methods

Math.abs(v): Returns the absolute value of v.
Math.acos(v): Returns the angle whose cosine is v.
Math.asin(v): Returns the angle whose sine is v.
Math.atan(v): Returns the angle whose tangent is v.
Math.atan2(y, x): Converts rectangular coordinates to polar coordinates (returns theta).
Math.cbrt(v): Returns the cube root of v.
Math.ceil(v): Returns the smallest double value that's greater than or equal to v (as an integer).
Math.cos(v): Returns the cosine of angle v.
Math.cosh(v): Returns the hyperbolic cosine of v.
Math.exp(v): Returns e to the power of v (Euler's number).
Math.expm1(v): Returns ev - 1.
Math.floor(v): Returns the largest double value that's less than or equal to v (as an integer).
Math.hypot(x, y): Returns the square root of (x² + y²).
Math.IEEEremainder(v1, v2): Returns the remainder of v1/v2.
Math.log(v): Returns the natural logarithm (base e) of v.
Math.log10(v): Returns the base-10 logarithm of v.
Math.log1p(v): Returns the natural logarithm of (1 + v).
Math.max(x, y): Returns the maximum value between x and y.
Math.min(x, y): Returns the minimum value between x and y.
Math.pow(x, y): Returns x to the power of y.
Math.random(): Returns a random value between 0.0 (inclusive) and 1.0 (exclusive).
Math.rint(v): Returns the closest integer to v.
Math.round(v): Returns the closest integer to v (as a long).
Math.signum(v): Returns -1 if v is negative, 0 if v is zero, and 1 if v is positive.
Math.sin(v): Returns the sine of angle v.
Math.sinh(v): Returns the hyperbolic sine of v.
Math.sqrt(v): Returns the square root of v.
Math.tan(v): Returns the tangent of angle v.
Math.toDegrees(v): Converts angle from radians to degrees.
Math.toRadians(v): Converts angle from degrees to radians.
Math.ulp(v): Returns the "ulp" (unit in the last place), the distance between v and the next larger double.

The String Type

Used for storing sequences of characters.
Example: String lastName = "Cat";
String literals are enclosed in double quotes.
Escape sequences can be used within literals.
String objects can be referenced by multiple handles.
String references can be set to null or empty strings.

String Methods

str.charAt(i): Returns the character at index i.
str.endsWith(str2): Checks if str ends with str2.
str.equals(str2): Checks if str and str2 are equal (case-sensitive).
str.equalsIgnoreCase(str2): Checks if str and str2 are equal (case-insensitive).
str.indexOf(ch): Returns the index of the first occurrence of character ch within str; -1 if not found.
str.indexOf(str2): Returns the index of the first occurrence of the string str2 within str; -1 if not present.
str.lastIndexOf(ch): Returns the index of the last occurrence of character ch within str; -1 if not present.
str.lastIndexOf(str2): Returns the index of the last occurrence of string str2 within str; -1 if not present.
str.length(): Returns the length of the string.
str.startsWith(str2): Checks if str starts with str2.
str.substring(start, stop): Extracts a substring.
str.toLowerCase(): Converts the string to lowercase.
str.toUpperCase(): Converts the string to uppercase.
str.trim(): Removes leading and trailing whitespace from the string.
String.valueOf(data_type): Converts data into String.

Concatenation

Joining strings using the + operator.
At least one operand must be a string.
word += "bye"; is a shortcut for concatenation and assignment.

The boolean Type

Holds one of two values: true (1) or false (0).
Used in logical expressions in control flow.
Relational operators are used to compare values:
- < (less than)
- (greater than)
- <= (less than or equal to)
- = (greater than or equal to)
- == (equal to)
- != (not equal to)
Logical operators are used to combine boolean expressions
- && (AND)
- || (OR)
- ! (NOT)
Example: boolean seniorStatus = age >= 65;